[bpf-next,v10,4/6] selftests/bpf: Add selftests for raw syncookie helpers

Commit Message

Maxim Mikityanskiy June 15, 2022, 1:48 p.m. UTC

This commit adds selftests for the new BPF helpers:
bpf_tcp_raw_{gen,check}_syncookie_ipv{4,6}.

xdp_synproxy_kern.c is a BPF program that generates SYN cookies on
allowed TCP ports and sends SYNACKs to clients, accelerating synproxy
iptables module.

xdp_synproxy.c is a userspace control application that allows to
configure the following options in runtime: list of allowed ports, MSS,
window scale, TTL.

A selftest is added to prog_tests that leverages the above programs to
test the functionality of the new helpers.

Signed-off-by: Maxim Mikityanskiy <[e-mail]>
Reviewed-by: Tariq Toukan <[e-mail]>
---
 tools/testing/selftests/bpf/.gitignore        |   1 +
 tools/testing/selftests/bpf/Makefile          |   3 +-
 .../selftests/bpf/prog_tests/xdp_synproxy.c   | 146 ++++
 .../selftests/bpf/progs/xdp_synproxy_kern.c   | 763 ++++++++++++++++++
 tools/testing/selftests/bpf/xdp_synproxy.c    | 418 ++++++++++
 5 files changed, 1330 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c
 create mode 100644 tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
 create mode 100644 tools/testing/selftests/bpf/xdp_synproxy.c

Comments

Yauheni Kaliuta July 7, 2022, 10:47 a.m. UTC | #1

Hi, Maxim!

The test is not buildable for me with CONFIG_NF_CONNTRACK=m due to
missing BPF_F_CURRENT_NETNS in vmlinux.h.

On Wed, Jun 15, 2022 at 4:49 PM Maxim Mikityanskiy <[e-mail]> wrote:
>
> This commit adds selftests for the new BPF helpers:
> bpf_tcp_raw_{gen,check}_syncookie_ipv{4,6}.
>
> xdp_synproxy_kern.c is a BPF program that generates SYN cookies on
> allowed TCP ports and sends SYNACKs to clients, accelerating synproxy
> iptables module.
>
> xdp_synproxy.c is a userspace control application that allows to
> configure the following options in runtime: list of allowed ports, MSS,
> window scale, TTL.
>
> A selftest is added to prog_tests that leverages the above programs to
> test the functionality of the new helpers.
>
> Signed-off-by: Maxim Mikityanskiy <[e-mail]>
> Reviewed-by: Tariq Toukan <[e-mail]>
> ---
>  tools/testing/selftests/bpf/.gitignore        |   1 +
>  tools/testing/selftests/bpf/Makefile          |   3 +-
>  .../selftests/bpf/prog_tests/xdp_synproxy.c   | 146 ++++
>  .../selftests/bpf/progs/xdp_synproxy_kern.c   | 763 ++++++++++++++++++
>  tools/testing/selftests/bpf/xdp_synproxy.c    | 418 ++++++++++
>  5 files changed, 1330 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c
>  create mode 100644 tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
>  create mode 100644 tools/testing/selftests/bpf/xdp_synproxy.c
>
> diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
> index 595565eb68c0..ca2f47f45670 100644
> --- a/tools/testing/selftests/bpf/.gitignore
> +++ b/tools/testing/selftests/bpf/.gitignore
> @@ -43,3 +43,4 @@ test_cpp
>  *.tmp
>  xdpxceiver
>  xdp_redirect_multi
> +xdp_synproxy
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 8ad7a733a505..e4ce21f4a474 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -82,7 +82,7 @@ TEST_PROGS_EXTENDED := with_addr.sh \
>  TEST_GEN_PROGS_EXTENDED = test_sock_addr test_skb_cgroup_id_user \
>         flow_dissector_load test_flow_dissector test_tcp_check_syncookie_user \
>         test_lirc_mode2_user xdping test_cpp runqslower bench bpf_testmod.ko \
> -       xdpxceiver xdp_redirect_multi
> +       xdpxceiver xdp_redirect_multi xdp_synproxy
>
>  TEST_CUSTOM_PROGS = $(OUTPUT)/urandom_read
>
> @@ -502,6 +502,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c      \
>                          cap_helpers.c
>  TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko \
>                        $(OUTPUT)/liburandom_read.so                     \
> +                      $(OUTPUT)/xdp_synproxy                           \
>                        ima_setup.sh                                     \
>                        $(wildcard progs/btf_dump_test_case_*.c)
>  TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c b/tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c
> new file mode 100644
> index 000000000000..d9ee884c2a2b
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c
> @@ -0,0 +1,146 @@
> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
> +/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
> +
> +#include <test_progs.h>
> +#include <network_helpers.h>
> +#include <ctype.h>
> +
> +#define CMD_OUT_BUF_SIZE 1023
> +
> +#define SYS(cmd) ({ \
> +       if (!ASSERT_OK(system(cmd), (cmd))) \
> +               goto out; \
> +})
> +
> +#define SYS_OUT(cmd) ({ \
> +       FILE *f = popen((cmd), "r"); \
> +       if (!ASSERT_OK_PTR(f, (cmd))) \
> +               goto out; \
> +       f; \
> +})
> +
> +/* out must be at least `size * 4 + 1` bytes long */
> +static void escape_str(char *out, const char *in, size_t size)
> +{
> +       static const char *hex = "0123456789ABCDEF";
> +       size_t i;
> +
> +       for (i = 0; i < size; i++) {
> +               if (isprint(in[i]) && in[i] != '\\' && in[i] != '\'') {
> +                       *out++ = in[i];
> +               } else {
> +                       *out++ = '\\';
> +                       *out++ = 'x';
> +                       *out++ = hex[(in[i] >> 4) & 0xf];
> +                       *out++ = hex[in[i] & 0xf];
> +               }
> +       }
> +       *out++ = '\0';
> +}
> +
> +static bool expect_str(char *buf, size_t size, const char *str, const char *name)
> +{
> +       static char escbuf_expected[CMD_OUT_BUF_SIZE * 4];
> +       static char escbuf_actual[CMD_OUT_BUF_SIZE * 4];
> +       static int duration = 0;
> +       bool ok;
> +
> +       ok = size == strlen(str) && !memcmp(buf, str, size);
> +
> +       if (!ok) {
> +               escape_str(escbuf_expected, str, strlen(str));
> +               escape_str(escbuf_actual, buf, size);
> +       }
> +       CHECK(!ok, name, "unexpected %s: actual '%s' != expected '%s'\n",
> +             name, escbuf_actual, escbuf_expected);
> +
> +       return ok;
> +}
> +
> +void test_xdp_synproxy(void)
> +{
> +       int server_fd = -1, client_fd = -1, accept_fd = -1;
> +       struct nstoken *ns = NULL;
> +       FILE *ctrl_file = NULL;
> +       char buf[CMD_OUT_BUF_SIZE];
> +       size_t size;
> +
> +       SYS("ip netns add synproxy");
> +
> +       SYS("ip link add tmp0 type veth peer name tmp1");
> +       SYS("ip link set tmp1 netns synproxy");
> +       SYS("ip link set tmp0 up");
> +       SYS("ip addr replace 198.18.0.1/24 dev tmp0");
> +
> +       /* When checksum offload is enabled, the XDP program sees wrong
> +        * checksums and drops packets.
> +        */
> +       SYS("ethtool -K tmp0 tx off");
> +       /* Workaround required for veth. */
> +       SYS("ip link set tmp0 xdp object xdp_dummy.o section xdp 2> /dev/null");
> +
> +       ns = open_netns("synproxy");
> +       if (!ASSERT_OK_PTR(ns, "setns"))
> +               goto out;
> +
> +       SYS("ip link set lo up");
> +       SYS("ip link set tmp1 up");
> +       SYS("ip addr replace 198.18.0.2/24 dev tmp1");
> +       SYS("sysctl -w net.ipv4.tcp_syncookies=2");
> +       SYS("sysctl -w net.ipv4.tcp_timestamps=1");
> +       SYS("sysctl -w net.netfilter.nf_conntrack_tcp_loose=0");
> +       SYS("iptables -t raw -I PREROUTING \
> +           -i tmp1 -p tcp -m tcp --syn --dport 8080 -j CT --notrack");
> +       SYS("iptables -t filter -A INPUT \
> +           -i tmp1 -p tcp -m tcp --dport 8080 -m state --state INVALID,UNTRACKED \
> +           -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460");
> +       SYS("iptables -t filter -A INPUT \
> +           -i tmp1 -m state --state INVALID -j DROP");
> +
> +       ctrl_file = SYS_OUT("./xdp_synproxy --iface tmp1 --ports 8080 --single \
> +                           --mss4 1460 --mss6 1440 --wscale 7 --ttl 64");
> +       size = fread(buf, 1, sizeof(buf), ctrl_file);
> +       pclose(ctrl_file);
> +       if (!expect_str(buf, size, "Total SYNACKs generated: 0\n",
> +                       "initial SYNACKs"))
> +               goto out;
> +
> +       server_fd = start_server(AF_INET, SOCK_STREAM, "198.18.0.2", 8080, 0);
> +       if (!ASSERT_GE(server_fd, 0, "start_server"))
> +               goto out;
> +
> +       close_netns(ns);
> +       ns = NULL;
> +
> +       client_fd = connect_to_fd(server_fd, 10000);
> +       if (!ASSERT_GE(client_fd, 0, "connect_to_fd"))
> +               goto out;
> +
> +       accept_fd = accept(server_fd, NULL, NULL);
> +       if (!ASSERT_GE(accept_fd, 0, "accept"))
> +               goto out;
> +
> +       ns = open_netns("synproxy");
> +       if (!ASSERT_OK_PTR(ns, "setns"))
> +               goto out;
> +
> +       ctrl_file = SYS_OUT("./xdp_synproxy --iface tmp1 --single");
> +       size = fread(buf, 1, sizeof(buf), ctrl_file);
> +       pclose(ctrl_file);
> +       if (!expect_str(buf, size, "Total SYNACKs generated: 1\n",
> +                       "SYNACKs after connection"))
> +               goto out;
> +
> +out:
> +       if (accept_fd >= 0)
> +               close(accept_fd);
> +       if (client_fd >= 0)
> +               close(client_fd);
> +       if (server_fd >= 0)
> +               close(server_fd);
> +       if (ns)
> +               close_netns(ns);
> +
> +       system("ip link del tmp0");
> +       system("ip netns del synproxy");
> +}
> diff --git a/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c b/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
> new file mode 100644
> index 000000000000..53b9865276a4
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
> @@ -0,0 +1,763 @@
> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
> +/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
> +
> +#include "vmlinux.h"
> +
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_endian.h>
> +#include <asm/errno.h>
> +
> +#define NSEC_PER_SEC 1000000000L
> +
> +#define ETH_ALEN 6
> +#define ETH_P_IP 0x0800
> +#define ETH_P_IPV6 0x86DD
> +
> +#define tcp_flag_word(tp) (((union tcp_word_hdr *)(tp))->words[3])
> +
> +#define IP_DF 0x4000
> +#define IP_MF 0x2000
> +#define IP_OFFSET 0x1fff
> +
> +#define NEXTHDR_TCP 6
> +
> +#define TCPOPT_NOP 1
> +#define TCPOPT_EOL 0
> +#define TCPOPT_MSS 2
> +#define TCPOPT_WINDOW 3
> +#define TCPOPT_SACK_PERM 4
> +#define TCPOPT_TIMESTAMP 8
> +
> +#define TCPOLEN_MSS 4
> +#define TCPOLEN_WINDOW 3
> +#define TCPOLEN_SACK_PERM 2
> +#define TCPOLEN_TIMESTAMP 10
> +
> +#define TCP_TS_HZ 1000
> +#define TS_OPT_WSCALE_MASK 0xf
> +#define TS_OPT_SACK (1 << 4)
> +#define TS_OPT_ECN (1 << 5)
> +#define TSBITS 6
> +#define TSMASK (((__u32)1 << TSBITS) - 1)
> +#define TCP_MAX_WSCALE 14U
> +
> +#define IPV4_MAXLEN 60
> +#define TCP_MAXLEN 60
> +
> +#define DEFAULT_MSS4 1460
> +#define DEFAULT_MSS6 1440
> +#define DEFAULT_WSCALE 7
> +#define DEFAULT_TTL 64
> +#define MAX_ALLOWED_PORTS 8
> +
> +#define swap(a, b) \
> +       do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
> +
> +#define __get_unaligned_t(type, ptr) ({                                                \
> +       const struct { type x; } __attribute__((__packed__)) *__pptr = (typeof(__pptr))(ptr); \
> +       __pptr->x;                                                              \
> +})
> +
> +#define get_unaligned(ptr) __get_unaligned_t(typeof(*(ptr)), (ptr))
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_ARRAY);
> +       __type(key, __u32);
> +       __type(value, __u64);
> +       __uint(max_entries, 2);
> +} values SEC(".maps");
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_ARRAY);
> +       __type(key, __u32);
> +       __type(value, __u16);
> +       __uint(max_entries, MAX_ALLOWED_PORTS);
> +} allowed_ports SEC(".maps");
> +
> +extern struct nf_conn *bpf_xdp_ct_lookup(struct xdp_md *xdp_ctx,
> +                                        struct bpf_sock_tuple *bpf_tuple,
> +                                        __u32 len_tuple,
> +                                        struct bpf_ct_opts *opts,
> +                                        __u32 len_opts) __ksym;
> +
> +extern void bpf_ct_release(struct nf_conn *ct) __ksym;
> +
> +static __always_inline void swap_eth_addr(__u8 *a, __u8 *b)
> +{
> +       __u8 tmp[ETH_ALEN];
> +
> +       __builtin_memcpy(tmp, a, ETH_ALEN);
> +       __builtin_memcpy(a, b, ETH_ALEN);
> +       __builtin_memcpy(b, tmp, ETH_ALEN);
> +}
> +
> +static __always_inline __u16 csum_fold(__u32 csum)
> +{
> +       csum = (csum & 0xffff) + (csum >> 16);
> +       csum = (csum & 0xffff) + (csum >> 16);
> +       return (__u16)~csum;
> +}
> +
> +static __always_inline __u16 csum_tcpudp_magic(__be32 saddr, __be32 daddr,
> +                                              __u32 len, __u8 proto,
> +                                              __u32 csum)
> +{
> +       __u64 s = csum;
> +
> +       s += (__u32)saddr;
> +       s += (__u32)daddr;
> +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
> +       s += proto + len;
> +#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> +       s += (proto + len) << 8;
> +#else
> +#error Unknown endian
> +#endif
> +       s = (s & 0xffffffff) + (s >> 32);
> +       s = (s & 0xffffffff) + (s >> 32);
> +
> +       return csum_fold((__u32)s);
> +}
> +
> +static __always_inline __u16 csum_ipv6_magic(const struct in6_addr *saddr,
> +                                            const struct in6_addr *daddr,
> +                                            __u32 len, __u8 proto, __u32 csum)
> +{
> +       __u64 sum = csum;
> +       int i;
> +
> +#pragma unroll
> +       for (i = 0; i < 4; i++)
> +               sum += (__u32)saddr->in6_u.u6_addr32[i];
> +
> +#pragma unroll
> +       for (i = 0; i < 4; i++)
> +               sum += (__u32)daddr->in6_u.u6_addr32[i];
> +
> +       /* Don't combine additions to avoid 32-bit overflow. */
> +       sum += bpf_htonl(len);
> +       sum += bpf_htonl(proto);
> +
> +       sum = (sum & 0xffffffff) + (sum >> 32);
> +       sum = (sum & 0xffffffff) + (sum >> 32);
> +
> +       return csum_fold((__u32)sum);
> +}
> +
> +static __always_inline __u64 tcp_clock_ns(void)
> +{
> +       return bpf_ktime_get_ns();
> +}
> +
> +static __always_inline __u32 tcp_ns_to_ts(__u64 ns)
> +{
> +       return ns / (NSEC_PER_SEC / TCP_TS_HZ);
> +}
> +
> +static __always_inline __u32 tcp_time_stamp_raw(void)
> +{
> +       return tcp_ns_to_ts(tcp_clock_ns());
> +}
> +
> +struct tcpopt_context {
> +       __u8 *ptr;
> +       __u8 *end;
> +       void *data_end;
> +       __be32 *tsecr;
> +       __u8 wscale;
> +       bool option_timestamp;
> +       bool option_sack;
> +};
> +
> +static int tscookie_tcpopt_parse(struct tcpopt_context *ctx)
> +{
> +       __u8 opcode, opsize;
> +
> +       if (ctx->ptr >= ctx->end)
> +               return 1;
> +       if (ctx->ptr >= ctx->data_end)
> +               return 1;
> +
> +       opcode = ctx->ptr[0];
> +
> +       if (opcode == TCPOPT_EOL)
> +               return 1;
> +       if (opcode == TCPOPT_NOP) {
> +               ++ctx->ptr;
> +               return 0;
> +       }
> +
> +       if (ctx->ptr + 1 >= ctx->end)
> +               return 1;
> +       if (ctx->ptr + 1 >= ctx->data_end)
> +               return 1;
> +       opsize = ctx->ptr[1];
> +       if (opsize < 2)
> +               return 1;
> +
> +       if (ctx->ptr + opsize > ctx->end)
> +               return 1;
> +
> +       switch (opcode) {
> +       case TCPOPT_WINDOW:
> +               if (opsize == TCPOLEN_WINDOW && ctx->ptr + TCPOLEN_WINDOW <= ctx->data_end)
> +                       ctx->wscale = ctx->ptr[2] < TCP_MAX_WSCALE ? ctx->ptr[2] : TCP_MAX_WSCALE;
> +               break;
> +       case TCPOPT_TIMESTAMP:
> +               if (opsize == TCPOLEN_TIMESTAMP && ctx->ptr + TCPOLEN_TIMESTAMP <= ctx->data_end) {
> +                       ctx->option_timestamp = true;
> +                       /* Client's tsval becomes our tsecr. */
> +                       *ctx->tsecr = get_unaligned((__be32 *)(ctx->ptr + 2));
> +               }
> +               break;
> +       case TCPOPT_SACK_PERM:
> +               if (opsize == TCPOLEN_SACK_PERM)
> +                       ctx->option_sack = true;
> +               break;
> +       }
> +
> +       ctx->ptr += opsize;
> +
> +       return 0;
> +}
> +
> +static int tscookie_tcpopt_parse_batch(__u32 index, void *context)
> +{
> +       int i;
> +
> +       for (i = 0; i < 7; i++)
> +               if (tscookie_tcpopt_parse(context))
> +                       return 1;
> +       return 0;
> +}
> +
> +static __always_inline bool tscookie_init(struct tcphdr *tcp_header,
> +                                         __u16 tcp_len, __be32 *tsval,
> +                                         __be32 *tsecr, void *data_end)
> +{
> +       struct tcpopt_context loop_ctx = {
> +               .ptr = (__u8 *)(tcp_header + 1),
> +               .end = (__u8 *)tcp_header + tcp_len,
> +               .data_end = data_end,
> +               .tsecr = tsecr,
> +               .wscale = TS_OPT_WSCALE_MASK,
> +               .option_timestamp = false,
> +               .option_sack = false,
> +       };
> +       u32 cookie;
> +
> +       bpf_loop(6, tscookie_tcpopt_parse_batch, &loop_ctx, 0);
> +
> +       if (!loop_ctx.option_timestamp)
> +               return false;
> +
> +       cookie = tcp_time_stamp_raw() & ~TSMASK;
> +       cookie |= loop_ctx.wscale & TS_OPT_WSCALE_MASK;
> +       if (loop_ctx.option_sack)
> +               cookie |= TS_OPT_SACK;
> +       if (tcp_header->ece && tcp_header->cwr)
> +               cookie |= TS_OPT_ECN;
> +       *tsval = bpf_htonl(cookie);
> +
> +       return true;
> +}
> +
> +static __always_inline void values_get_tcpipopts(__u16 *mss, __u8 *wscale,
> +                                                __u8 *ttl, bool ipv6)
> +{
> +       __u32 key = 0;
> +       __u64 *value;
> +
> +       value = bpf_map_lookup_elem(&values, &key);
> +       if (value && *value != 0) {
> +               if (ipv6)
> +                       *mss = (*value >> 32) & 0xffff;
> +               else
> +                       *mss = *value & 0xffff;
> +               *wscale = (*value >> 16) & 0xf;
> +               *ttl = (*value >> 24) & 0xff;
> +               return;
> +       }
> +
> +       *mss = ipv6 ? DEFAULT_MSS6 : DEFAULT_MSS4;
> +       *wscale = DEFAULT_WSCALE;
> +       *ttl = DEFAULT_TTL;
> +}
> +
> +static __always_inline void values_inc_synacks(void)
> +{
> +       __u32 key = 1;
> +       __u32 *value;
> +
> +       value = bpf_map_lookup_elem(&values, &key);
> +       if (value)
> +               __sync_fetch_and_add(value, 1);
> +}
> +
> +static __always_inline bool check_port_allowed(__u16 port)
> +{
> +       __u32 i;
> +
> +       for (i = 0; i < MAX_ALLOWED_PORTS; i++) {
> +               __u32 key = i;
> +               __u16 *value;
> +
> +               value = bpf_map_lookup_elem(&allowed_ports, &key);
> +
> +               if (!value)
> +                       break;
> +               /* 0 is a terminator value. Check it first to avoid matching on
> +                * a forbidden port == 0 and returning true.
> +                */
> +               if (*value == 0)
> +                       break;
> +
> +               if (*value == port)
> +                       return true;
> +       }
> +
> +       return false;
> +}
> +
> +struct header_pointers {
> +       struct ethhdr *eth;
> +       struct iphdr *ipv4;
> +       struct ipv6hdr *ipv6;
> +       struct tcphdr *tcp;
> +       __u16 tcp_len;
> +};
> +
> +static __always_inline int tcp_dissect(void *data, void *data_end,
> +                                      struct header_pointers *hdr)
> +{
> +       hdr->eth = data;
> +       if (hdr->eth + 1 > data_end)
> +               return XDP_DROP;
> +
> +       switch (bpf_ntohs(hdr->eth->h_proto)) {
> +       case ETH_P_IP:
> +               hdr->ipv6 = NULL;
> +
> +               hdr->ipv4 = (void *)hdr->eth + sizeof(*hdr->eth);
> +               if (hdr->ipv4 + 1 > data_end)
> +                       return XDP_DROP;
> +               if (hdr->ipv4->ihl * 4 < sizeof(*hdr->ipv4))
> +                       return XDP_DROP;
> +               if (hdr->ipv4->version != 4)
> +                       return XDP_DROP;
> +
> +               if (hdr->ipv4->protocol != IPPROTO_TCP)
> +                       return XDP_PASS;
> +
> +               hdr->tcp = (void *)hdr->ipv4 + hdr->ipv4->ihl * 4;
> +               break;
> +       case ETH_P_IPV6:
> +               hdr->ipv4 = NULL;
> +
> +               hdr->ipv6 = (void *)hdr->eth + sizeof(*hdr->eth);
> +               if (hdr->ipv6 + 1 > data_end)
> +                       return XDP_DROP;
> +               if (hdr->ipv6->version != 6)
> +                       return XDP_DROP;
> +
> +               /* XXX: Extension headers are not supported and could circumvent
> +                * XDP SYN flood protection.
> +                */
> +               if (hdr->ipv6->nexthdr != NEXTHDR_TCP)
> +                       return XDP_PASS;
> +
> +               hdr->tcp = (void *)hdr->ipv6 + sizeof(*hdr->ipv6);
> +               break;
> +       default:
> +               /* XXX: VLANs will circumvent XDP SYN flood protection. */
> +               return XDP_PASS;
> +       }
> +
> +       if (hdr->tcp + 1 > data_end)
> +               return XDP_DROP;
> +       hdr->tcp_len = hdr->tcp->doff * 4;
> +       if (hdr->tcp_len < sizeof(*hdr->tcp))
> +               return XDP_DROP;
> +
> +       return XDP_TX;
> +}
> +
> +static __always_inline int tcp_lookup(struct xdp_md *ctx, struct header_pointers *hdr)
> +{
> +       struct bpf_ct_opts ct_lookup_opts = {
> +               .netns_id = BPF_F_CURRENT_NETNS,
> +               .l4proto = IPPROTO_TCP,
> +       };
> +       struct bpf_sock_tuple tup = {};
> +       struct nf_conn *ct;
> +       __u32 tup_size;
> +
> +       if (hdr->ipv4) {
> +               /* TCP doesn't normally use fragments, and XDP can't reassemble
> +                * them.
> +                */
> +               if ((hdr->ipv4->frag_off & bpf_htons(IP_DF | IP_MF | IP_OFFSET)) != bpf_htons(IP_DF))
> +                       return XDP_DROP;
> +
> +               tup.ipv4.saddr = hdr->ipv4->saddr;
> +               tup.ipv4.daddr = hdr->ipv4->daddr;
> +               tup.ipv4.sport = hdr->tcp->source;
> +               tup.ipv4.dport = hdr->tcp->dest;
> +               tup_size = sizeof(tup.ipv4);
> +       } else if (hdr->ipv6) {
> +               __builtin_memcpy(tup.ipv6.saddr, &hdr->ipv6->saddr, sizeof(tup.ipv6.saddr));
> +               __builtin_memcpy(tup.ipv6.daddr, &hdr->ipv6->daddr, sizeof(tup.ipv6.daddr));
> +               tup.ipv6.sport = hdr->tcp->source;
> +               tup.ipv6.dport = hdr->tcp->dest;
> +               tup_size = sizeof(tup.ipv6);
> +       } else {
> +               /* The verifier can't track that either ipv4 or ipv6 is not
> +                * NULL.
> +                */
> +               return XDP_ABORTED;
> +       }
> +       ct = bpf_xdp_ct_lookup(ctx, &tup, tup_size, &ct_lookup_opts, sizeof(ct_lookup_opts));
> +       if (ct) {
> +               unsigned long status = ct->status;
> +
> +               bpf_ct_release(ct);
> +               if (status & IPS_CONFIRMED_BIT)
> +                       return XDP_PASS;
> +       } else if (ct_lookup_opts.error != -ENOENT) {
> +               return XDP_ABORTED;
> +       }
> +
> +       /* error == -ENOENT || !(status & IPS_CONFIRMED_BIT) */
> +       return XDP_TX;
> +}
> +
> +static __always_inline __u8 tcp_mkoptions(__be32 *buf, __be32 *tsopt, __u16 mss,
> +                                         __u8 wscale)
> +{
> +       __be32 *start = buf;
> +
> +       *buf++ = bpf_htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | mss);
> +
> +       if (!tsopt)
> +               return buf - start;
> +
> +       if (tsopt[0] & bpf_htonl(1 << 4))
> +               *buf++ = bpf_htonl((TCPOPT_SACK_PERM << 24) |
> +                                  (TCPOLEN_SACK_PERM << 16) |
> +                                  (TCPOPT_TIMESTAMP << 8) |
> +                                  TCPOLEN_TIMESTAMP);
> +       else
> +               *buf++ = bpf_htonl((TCPOPT_NOP << 24) |
> +                                  (TCPOPT_NOP << 16) |
> +                                  (TCPOPT_TIMESTAMP << 8) |
> +                                  TCPOLEN_TIMESTAMP);
> +       *buf++ = tsopt[0];
> +       *buf++ = tsopt[1];
> +
> +       if ((tsopt[0] & bpf_htonl(0xf)) != bpf_htonl(0xf))
> +               *buf++ = bpf_htonl((TCPOPT_NOP << 24) |
> +                                  (TCPOPT_WINDOW << 16) |
> +                                  (TCPOLEN_WINDOW << 8) |
> +                                  wscale);
> +
> +       return buf - start;
> +}
> +
> +static __always_inline void tcp_gen_synack(struct tcphdr *tcp_header,
> +                                          __u32 cookie, __be32 *tsopt,
> +                                          __u16 mss, __u8 wscale)
> +{
> +       void *tcp_options;
> +
> +       tcp_flag_word(tcp_header) = TCP_FLAG_SYN | TCP_FLAG_ACK;
> +       if (tsopt && (tsopt[0] & bpf_htonl(1 << 5)))
> +               tcp_flag_word(tcp_header) |= TCP_FLAG_ECE;
> +       tcp_header->doff = 5; /* doff is part of tcp_flag_word. */
> +       swap(tcp_header->source, tcp_header->dest);
> +       tcp_header->ack_seq = bpf_htonl(bpf_ntohl(tcp_header->seq) + 1);
> +       tcp_header->seq = bpf_htonl(cookie);
> +       tcp_header->window = 0;
> +       tcp_header->urg_ptr = 0;
> +       tcp_header->check = 0; /* Calculate checksum later. */
> +
> +       tcp_options = (void *)(tcp_header + 1);
> +       tcp_header->doff += tcp_mkoptions(tcp_options, tsopt, mss, wscale);
> +}
> +
> +static __always_inline void tcpv4_gen_synack(struct header_pointers *hdr,
> +                                            __u32 cookie, __be32 *tsopt)
> +{
> +       __u8 wscale;
> +       __u16 mss;
> +       __u8 ttl;
> +
> +       values_get_tcpipopts(&mss, &wscale, &ttl, false);
> +
> +       swap_eth_addr(hdr->eth->h_source, hdr->eth->h_dest);
> +
> +       swap(hdr->ipv4->saddr, hdr->ipv4->daddr);
> +       hdr->ipv4->check = 0; /* Calculate checksum later. */
> +       hdr->ipv4->tos = 0;
> +       hdr->ipv4->id = 0;
> +       hdr->ipv4->ttl = ttl;
> +
> +       tcp_gen_synack(hdr->tcp, cookie, tsopt, mss, wscale);
> +
> +       hdr->tcp_len = hdr->tcp->doff * 4;
> +       hdr->ipv4->tot_len = bpf_htons(sizeof(*hdr->ipv4) + hdr->tcp_len);
> +}
> +
> +static __always_inline void tcpv6_gen_synack(struct header_pointers *hdr,
> +                                            __u32 cookie, __be32 *tsopt)
> +{
> +       __u8 wscale;
> +       __u16 mss;
> +       __u8 ttl;
> +
> +       values_get_tcpipopts(&mss, &wscale, &ttl, true);
> +
> +       swap_eth_addr(hdr->eth->h_source, hdr->eth->h_dest);
> +
> +       swap(hdr->ipv6->saddr, hdr->ipv6->daddr);
> +       *(__be32 *)hdr->ipv6 = bpf_htonl(0x60000000);
> +       hdr->ipv6->hop_limit = ttl;
> +
> +       tcp_gen_synack(hdr->tcp, cookie, tsopt, mss, wscale);
> +
> +       hdr->tcp_len = hdr->tcp->doff * 4;
> +       hdr->ipv6->payload_len = bpf_htons(hdr->tcp_len);
> +}
> +
> +static __always_inline int syncookie_handle_syn(struct header_pointers *hdr,
> +                                               struct xdp_md *ctx,
> +                                               void *data, void *data_end)
> +{
> +       __u32 old_pkt_size, new_pkt_size;
> +       /* Unlike clang 10, clang 11 and 12 generate code that doesn't pass the
> +        * BPF verifier if tsopt is not volatile. Volatile forces it to store
> +        * the pointer value and use it directly, otherwise tcp_mkoptions is
> +        * (mis)compiled like this:
> +        *   if (!tsopt)
> +        *       return buf - start;
> +        *   reg = stored_return_value_of_tscookie_init;
> +        *   if (reg)
> +        *       tsopt = tsopt_buf;
> +        *   else
> +        *       tsopt = NULL;
> +        *   ...
> +        *   *buf++ = tsopt[1];
> +        * It creates a dead branch where tsopt is assigned NULL, but the
> +        * verifier can't prove it's dead and blocks the program.
> +        */
> +       __be32 * volatile tsopt = NULL;
> +       __be32 tsopt_buf[2] = {};
> +       __u16 ip_len;
> +       __u32 cookie;
> +       __s64 value;
> +
> +       /* Checksum is not yet verified, but both checksum failure and TCP
> +        * header checks return XDP_DROP, so the order doesn't matter.
> +        */
> +       if (hdr->tcp->fin || hdr->tcp->rst)
> +               return XDP_DROP;
> +
> +       /* Issue SYN cookies on allowed ports, drop SYN packets on blocked
> +        * ports.
> +        */
> +       if (!check_port_allowed(bpf_ntohs(hdr->tcp->dest)))
> +               return XDP_DROP;
> +
> +       if (hdr->ipv4) {
> +               /* Check the IPv4 and TCP checksums before creating a SYNACK. */
> +               value = bpf_csum_diff(0, 0, (void *)hdr->ipv4, hdr->ipv4->ihl * 4, 0);
> +               if (value < 0)
> +                       return XDP_ABORTED;
> +               if (csum_fold(value) != 0)
> +                       return XDP_DROP; /* Bad IPv4 checksum. */
> +
> +               value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
> +               if (value < 0)
> +                       return XDP_ABORTED;
> +               if (csum_tcpudp_magic(hdr->ipv4->saddr, hdr->ipv4->daddr,
> +                                     hdr->tcp_len, IPPROTO_TCP, value) != 0)
> +                       return XDP_DROP; /* Bad TCP checksum. */
> +
> +               ip_len = sizeof(*hdr->ipv4);
> +
> +               value = bpf_tcp_raw_gen_syncookie_ipv4(hdr->ipv4, hdr->tcp,
> +                                                      hdr->tcp_len);
> +       } else if (hdr->ipv6) {
> +               /* Check the TCP checksum before creating a SYNACK. */
> +               value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
> +               if (value < 0)
> +                       return XDP_ABORTED;
> +               if (csum_ipv6_magic(&hdr->ipv6->saddr, &hdr->ipv6->daddr,
> +                                   hdr->tcp_len, IPPROTO_TCP, value) != 0)
> +                       return XDP_DROP; /* Bad TCP checksum. */
> +
> +               ip_len = sizeof(*hdr->ipv6);
> +
> +               value = bpf_tcp_raw_gen_syncookie_ipv6(hdr->ipv6, hdr->tcp,
> +                                                      hdr->tcp_len);
> +       } else {
> +               return XDP_ABORTED;
> +       }
> +
> +       if (value < 0)
> +               return XDP_ABORTED;
> +       cookie = (__u32)value;
> +
> +       if (tscookie_init((void *)hdr->tcp, hdr->tcp_len,
> +                         &tsopt_buf[0], &tsopt_buf[1], data_end))
> +               tsopt = tsopt_buf;
> +
> +       /* Check that there is enough space for a SYNACK. It also covers
> +        * the check that the destination of the __builtin_memmove below
> +        * doesn't overflow.
> +        */
> +       if (data + sizeof(*hdr->eth) + ip_len + TCP_MAXLEN > data_end)
> +               return XDP_ABORTED;
> +
> +       if (hdr->ipv4) {
> +               if (hdr->ipv4->ihl * 4 > sizeof(*hdr->ipv4)) {
> +                       struct tcphdr *new_tcp_header;
> +
> +                       new_tcp_header = data + sizeof(*hdr->eth) + sizeof(*hdr->ipv4);
> +                       __builtin_memmove(new_tcp_header, hdr->tcp, sizeof(*hdr->tcp));
> +                       hdr->tcp = new_tcp_header;
> +
> +                       hdr->ipv4->ihl = sizeof(*hdr->ipv4) / 4;
> +               }
> +
> +               tcpv4_gen_synack(hdr, cookie, tsopt);
> +       } else if (hdr->ipv6) {
> +               tcpv6_gen_synack(hdr, cookie, tsopt);
> +       } else {
> +               return XDP_ABORTED;
> +       }
> +
> +       /* Recalculate checksums. */
> +       hdr->tcp->check = 0;
> +       value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
> +       if (value < 0)
> +               return XDP_ABORTED;
> +       if (hdr->ipv4) {
> +               hdr->tcp->check = csum_tcpudp_magic(hdr->ipv4->saddr,
> +                                                   hdr->ipv4->daddr,
> +                                                   hdr->tcp_len,
> +                                                   IPPROTO_TCP,
> +                                                   value);
> +
> +               hdr->ipv4->check = 0;
> +               value = bpf_csum_diff(0, 0, (void *)hdr->ipv4, sizeof(*hdr->ipv4), 0);
> +               if (value < 0)
> +                       return XDP_ABORTED;
> +               hdr->ipv4->check = csum_fold(value);
> +       } else if (hdr->ipv6) {
> +               hdr->tcp->check = csum_ipv6_magic(&hdr->ipv6->saddr,
> +                                                 &hdr->ipv6->daddr,
> +                                                 hdr->tcp_len,
> +                                                 IPPROTO_TCP,
> +                                                 value);
> +       } else {
> +               return XDP_ABORTED;
> +       }
> +
> +       /* Set the new packet size. */
> +       old_pkt_size = data_end - data;
> +       new_pkt_size = sizeof(*hdr->eth) + ip_len + hdr->tcp->doff * 4;
> +       if (bpf_xdp_adjust_tail(ctx, new_pkt_size - old_pkt_size))
> +               return XDP_ABORTED;
> +
> +       values_inc_synacks();
> +
> +       return XDP_TX;
> +}
> +
> +static __always_inline int syncookie_handle_ack(struct header_pointers *hdr)
> +{
> +       int err;
> +
> +       if (hdr->tcp->rst)
> +               return XDP_DROP;
> +
> +       if (hdr->ipv4)
> +               err = bpf_tcp_raw_check_syncookie_ipv4(hdr->ipv4, hdr->tcp);
> +       else if (hdr->ipv6)
> +               err = bpf_tcp_raw_check_syncookie_ipv6(hdr->ipv6, hdr->tcp);
> +       else
> +               return XDP_ABORTED;
> +       if (err)
> +               return XDP_DROP;
> +
> +       return XDP_PASS;
> +}
> +
> +SEC("xdp")
> +int syncookie_xdp(struct xdp_md *ctx)
> +{
> +       void *data_end = (void *)(long)ctx->data_end;
> +       void *data = (void *)(long)ctx->data;
> +       struct header_pointers hdr;
> +       __s64 value;
> +       int ret;
> +
> +       struct bpf_ct_opts ct_lookup_opts = {
> +               .netns_id = BPF_F_CURRENT_NETNS,
> +               .l4proto = IPPROTO_TCP,
> +       };
> +
> +       ret = tcp_dissect(data, data_end, &hdr);
> +       if (ret != XDP_TX)
> +               return ret;
> +
> +       ret = tcp_lookup(ctx, &hdr);
> +       if (ret != XDP_TX)
> +               return ret;
> +
> +       /* Packet is TCP and doesn't belong to an established connection. */
> +
> +       if ((hdr.tcp->syn ^ hdr.tcp->ack) != 1)
> +               return XDP_DROP;
> +
> +       /* Grow the TCP header to TCP_MAXLEN to be able to pass any hdr.tcp_len
> +        * to bpf_tcp_raw_gen_syncookie_ipv{4,6} and pass the verifier.
> +        */
> +       if (bpf_xdp_adjust_tail(ctx, TCP_MAXLEN - hdr.tcp_len))
> +               return XDP_ABORTED;
> +
> +       data_end = (void *)(long)ctx->data_end;
> +       data = (void *)(long)ctx->data;
> +
> +       if (hdr.ipv4) {
> +               hdr.eth = data;
> +               hdr.ipv4 = (void *)hdr.eth + sizeof(*hdr.eth);
> +               /* IPV4_MAXLEN is needed when calculating checksum.
> +                * At least sizeof(struct iphdr) is needed here to access ihl.
> +                */
> +               if ((void *)hdr.ipv4 + IPV4_MAXLEN > data_end)
> +                       return XDP_ABORTED;
> +               hdr.tcp = (void *)hdr.ipv4 + hdr.ipv4->ihl * 4;
> +       } else if (hdr.ipv6) {
> +               hdr.eth = data;
> +               hdr.ipv6 = (void *)hdr.eth + sizeof(*hdr.eth);
> +               hdr.tcp = (void *)hdr.ipv6 + sizeof(*hdr.ipv6);
> +       } else {
> +               return XDP_ABORTED;
> +       }
> +
> +       if ((void *)hdr.tcp + TCP_MAXLEN > data_end)
> +               return XDP_ABORTED;
> +
> +       /* We run out of registers, tcp_len gets spilled to the stack, and the
> +        * verifier forgets its min and max values checked above in tcp_dissect.
> +        */
> +       hdr.tcp_len = hdr.tcp->doff * 4;
> +       if (hdr.tcp_len < sizeof(*hdr.tcp))
> +               return XDP_ABORTED;
> +
> +       return hdr.tcp->syn ? syncookie_handle_syn(&hdr, ctx, data, data_end) :
> +                             syncookie_handle_ack(&hdr);
> +}
> +
> +char _license[] SEC("license") = "GPL";
> diff --git a/tools/testing/selftests/bpf/xdp_synproxy.c b/tools/testing/selftests/bpf/xdp_synproxy.c
> new file mode 100644
> index 000000000000..4653d4655b5f
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/xdp_synproxy.c
> @@ -0,0 +1,418 @@
> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
> +/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
> +
> +#include <stdnoreturn.h>
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <unistd.h>
> +#include <getopt.h>
> +#include <signal.h>
> +#include <sys/types.h>
> +#include <bpf/bpf.h>
> +#include <bpf/libbpf.h>
> +#include <net/if.h>
> +#include <linux/if_link.h>
> +#include <linux/limits.h>
> +
> +static unsigned int ifindex;
> +static __u32 attached_prog_id;
> +
> +static void noreturn cleanup(int sig)
> +{
> +       DECLARE_LIBBPF_OPTS(bpf_xdp_attach_opts, opts);
> +       int prog_fd;
> +       int err;
> +
> +       if (attached_prog_id == 0)
> +               exit(0);
> +
> +       prog_fd = bpf_prog_get_fd_by_id(attached_prog_id);
> +       if (prog_fd < 0) {
> +               fprintf(stderr, "Error: bpf_prog_get_fd_by_id: %s\n", strerror(-prog_fd));
> +               err = bpf_xdp_attach(ifindex, -1, 0, NULL);
> +               if (err < 0) {
> +                       fprintf(stderr, "Error: bpf_set_link_xdp_fd: %s\n", strerror(-err));
> +                       fprintf(stderr, "Failed to detach XDP program\n");
> +                       exit(1);
> +               }
> +       } else {
> +               opts.old_prog_fd = prog_fd;
> +               err = bpf_xdp_attach(ifindex, -1, XDP_FLAGS_REPLACE, &opts);
> +               close(prog_fd);
> +               if (err < 0) {
> +                       fprintf(stderr, "Error: bpf_set_link_xdp_fd_opts: %s\n", strerror(-err));
> +                       /* Not an error if already replaced by someone else. */
> +                       if (err != -EEXIST) {
> +                               fprintf(stderr, "Failed to detach XDP program\n");
> +                               exit(1);
> +                       }
> +               }
> +       }
> +       exit(0);
> +}
> +
> +static noreturn void usage(const char *progname)
> +{
> +       fprintf(stderr, "Usage: %s [--iface <iface>|--prog <prog_id>] [--mss4 <mss ipv4> --mss6 <mss ipv6> --wscale <wscale> --ttl <ttl>] [--ports <port1>,<port2>,...] [--single]\n",
> +               progname);
> +       exit(1);
> +}
> +
> +static unsigned long parse_arg_ul(const char *progname, const char *arg, unsigned long limit)
> +{
> +       unsigned long res;
> +       char *endptr;
> +
> +       errno = 0;
> +       res = strtoul(arg, &endptr, 10);
> +       if (errno != 0 || *endptr != '\0' || arg[0] == '\0' || res > limit)
> +               usage(progname);
> +
> +       return res;
> +}
> +
> +static void parse_options(int argc, char *argv[], unsigned int *ifindex, __u32 *prog_id,
> +                         __u64 *tcpipopts, char **ports, bool *single)
> +{
> +       static struct option long_options[] = {
> +               { "help", no_argument, NULL, 'h' },
> +               { "iface", required_argument, NULL, 'i' },
> +               { "prog", required_argument, NULL, 'x' },
> +               { "mss4", required_argument, NULL, 4 },
> +               { "mss6", required_argument, NULL, 6 },
> +               { "wscale", required_argument, NULL, 'w' },
> +               { "ttl", required_argument, NULL, 't' },
> +               { "ports", required_argument, NULL, 'p' },
> +               { "single", no_argument, NULL, 's' },
> +               { NULL, 0, NULL, 0 },
> +       };
> +       unsigned long mss4, mss6, wscale, ttl;
> +       unsigned int tcpipopts_mask = 0;
> +
> +       if (argc < 2)
> +               usage(argv[0]);
> +
> +       *ifindex = 0;
> +       *prog_id = 0;
> +       *tcpipopts = 0;
> +       *ports = NULL;
> +       *single = false;
> +
> +       while (true) {
> +               int opt;
> +
> +               opt = getopt_long(argc, argv, "", long_options, NULL);
> +               if (opt == -1)
> +                       break;
> +
> +               switch (opt) {
> +               case 'h':
> +                       usage(argv[0]);
> +                       break;
> +               case 'i':
> +                       *ifindex = if_nametoindex(optarg);
> +                       if (*ifindex == 0)
> +                               usage(argv[0]);
> +                       break;
> +               case 'x':
> +                       *prog_id = parse_arg_ul(argv[0], optarg, UINT32_MAX);
> +                       if (*prog_id == 0)
> +                               usage(argv[0]);
> +                       break;
> +               case 4:
> +                       mss4 = parse_arg_ul(argv[0], optarg, UINT16_MAX);
> +                       tcpipopts_mask |= 1 << 0;
> +                       break;
> +               case 6:
> +                       mss6 = parse_arg_ul(argv[0], optarg, UINT16_MAX);
> +                       tcpipopts_mask |= 1 << 1;
> +                       break;
> +               case 'w':
> +                       wscale = parse_arg_ul(argv[0], optarg, 14);
> +                       tcpipopts_mask |= 1 << 2;
> +                       break;
> +               case 't':
> +                       ttl = parse_arg_ul(argv[0], optarg, UINT8_MAX);
> +                       tcpipopts_mask |= 1 << 3;
> +                       break;
> +               case 'p':
> +                       *ports = optarg;
> +                       break;
> +               case 's':
> +                       *single = true;
> +                       break;
> +               default:
> +                       usage(argv[0]);
> +               }
> +       }
> +       if (optind < argc)
> +               usage(argv[0]);
> +
> +       if (tcpipopts_mask == 0xf) {
> +               if (mss4 == 0 || mss6 == 0 || wscale == 0 || ttl == 0)
> +                       usage(argv[0]);
> +               *tcpipopts = (mss6 << 32) | (ttl << 24) | (wscale << 16) | mss4;
> +       } else if (tcpipopts_mask != 0) {
> +               usage(argv[0]);
> +       }
> +
> +       if (*ifindex != 0 && *prog_id != 0)
> +               usage(argv[0]);
> +       if (*ifindex == 0 && *prog_id == 0)
> +               usage(argv[0]);
> +}
> +
> +static int syncookie_attach(const char *argv0, unsigned int ifindex)
> +{
> +       struct bpf_prog_info info = {};
> +       __u32 info_len = sizeof(info);
> +       char xdp_filename[PATH_MAX];
> +       struct bpf_program *prog;
> +       struct bpf_object *obj;
> +       int prog_fd;
> +       int err;
> +
> +       snprintf(xdp_filename, sizeof(xdp_filename), "%s_kern.o", argv0);
> +       obj = bpf_object__open_file(xdp_filename, NULL);
> +       err = libbpf_get_error(obj);
> +       if (err < 0) {
> +               fprintf(stderr, "Error: bpf_object__open_file: %s\n", strerror(-err));
> +               return err;
> +       }
> +
> +       err = bpf_object__load(obj);
> +       if (err < 0) {
> +               fprintf(stderr, "Error: bpf_object__open_file: %s\n", strerror(-err));
> +               return err;
> +       }
> +
> +       prog = bpf_object__find_program_by_name(obj, "syncookie_xdp");
> +       if (!prog) {
> +               fprintf(stderr, "Error: bpf_object__find_program_by_name: program syncookie_xdp was not found\n");
> +               return -ENOENT;
> +       }
> +
> +       prog_fd = bpf_program__fd(prog);
> +
> +       err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
> +       if (err < 0) {
> +               fprintf(stderr, "Error: bpf_obj_get_info_by_fd: %s\n", strerror(-err));
> +               goto out;
> +       }
> +       attached_prog_id = info.id;
> +       signal(SIGINT, cleanup);
> +       signal(SIGTERM, cleanup);
> +       err = bpf_xdp_attach(ifindex, prog_fd, XDP_FLAGS_UPDATE_IF_NOEXIST, NULL);
> +       if (err < 0) {
> +               fprintf(stderr, "Error: bpf_set_link_xdp_fd: %s\n", strerror(-err));
> +               signal(SIGINT, SIG_DFL);
> +               signal(SIGTERM, SIG_DFL);
> +               attached_prog_id = 0;
> +               goto out;
> +       }
> +       err = 0;
> +out:
> +       bpf_object__close(obj);
> +       return err;
> +}
> +
> +static int syncookie_open_bpf_maps(__u32 prog_id, int *values_map_fd, int *ports_map_fd)
> +{
> +       struct bpf_prog_info prog_info;
> +       __u32 map_ids[8];
> +       __u32 info_len;
> +       int prog_fd;
> +       int err;
> +       int i;
> +
> +       *values_map_fd = -1;
> +       *ports_map_fd = -1;
> +
> +       prog_fd = bpf_prog_get_fd_by_id(prog_id);
> +       if (prog_fd < 0) {
> +               fprintf(stderr, "Error: bpf_prog_get_fd_by_id: %s\n", strerror(-prog_fd));
> +               return prog_fd;
> +       }
> +
> +       prog_info = (struct bpf_prog_info) {
> +               .nr_map_ids = 8,
> +               .map_ids = (__u64)map_ids,
> +       };
> +       info_len = sizeof(prog_info);
> +
> +       err = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &info_len);
> +       if (err != 0) {
> +               fprintf(stderr, "Error: bpf_obj_get_info_by_fd: %s\n", strerror(-err));
> +               goto out;
> +       }
> +
> +       if (prog_info.type != BPF_PROG_TYPE_XDP) {
> +               fprintf(stderr, "Error: BPF prog type is not BPF_PROG_TYPE_XDP\n");
> +               err = -ENOENT;
> +               goto out;
> +       }
> +       if (prog_info.nr_map_ids < 2) {
> +               fprintf(stderr, "Error: Found %u BPF maps, expected at least 2\n",
> +                       prog_info.nr_map_ids);
> +               err = -ENOENT;
> +               goto out;
> +       }
> +
> +       for (i = 0; i < prog_info.nr_map_ids; i++) {
> +               struct bpf_map_info map_info = {};
> +               int map_fd;
> +
> +               err = bpf_map_get_fd_by_id(map_ids[i]);
> +               if (err < 0) {
> +                       fprintf(stderr, "Error: bpf_map_get_fd_by_id: %s\n", strerror(-err));
> +                       goto err_close_map_fds;
> +               }
> +               map_fd = err;
> +
> +               info_len = sizeof(map_info);
> +               err = bpf_obj_get_info_by_fd(map_fd, &map_info, &info_len);
> +               if (err != 0) {
> +                       fprintf(stderr, "Error: bpf_obj_get_info_by_fd: %s\n", strerror(-err));
> +                       close(map_fd);
> +                       goto err_close_map_fds;
> +               }
> +               if (strcmp(map_info.name, "values") == 0) {
> +                       *values_map_fd = map_fd;
> +                       continue;
> +               }
> +               if (strcmp(map_info.name, "allowed_ports") == 0) {
> +                       *ports_map_fd = map_fd;
> +                       continue;
> +               }
> +               close(map_fd);
> +       }
> +
> +       if (*values_map_fd != -1 && *ports_map_fd != -1) {
> +               err = 0;
> +               goto out;
> +       }
> +
> +       err = -ENOENT;
> +
> +err_close_map_fds:
> +       if (*values_map_fd != -1)
> +               close(*values_map_fd);
> +       if (*ports_map_fd != -1)
> +               close(*ports_map_fd);
> +       *values_map_fd = -1;
> +       *ports_map_fd = -1;
> +
> +out:
> +       close(prog_fd);
> +       return err;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +       int values_map_fd, ports_map_fd;
> +       __u64 tcpipopts;
> +       bool firstiter;
> +       __u64 prevcnt;
> +       __u32 prog_id;
> +       char *ports;
> +       bool single;
> +       int err = 0;
> +
> +       parse_options(argc, argv, &ifindex, &prog_id, &tcpipopts, &ports, &single);
> +
> +       if (prog_id == 0) {
> +               err = bpf_xdp_query_id(ifindex, 0, &prog_id);
> +               if (err < 0) {
> +                       fprintf(stderr, "Error: bpf_get_link_xdp_id: %s\n", strerror(-err));
> +                       goto out;
> +               }
> +               if (prog_id == 0) {
> +                       err = syncookie_attach(argv[0], ifindex);
> +                       if (err < 0)
> +                               goto out;
> +                       prog_id = attached_prog_id;
> +               }
> +       }
> +
> +       err = syncookie_open_bpf_maps(prog_id, &values_map_fd, &ports_map_fd);
> +       if (err < 0)
> +               goto out;
> +
> +       if (ports) {
> +               __u16 port_last = 0;
> +               __u32 port_idx = 0;
> +               char *p = ports;
> +
> +               fprintf(stderr, "Replacing allowed ports\n");
> +
> +               while (p && *p != '\0') {
> +                       char *token = strsep(&p, ",");
> +                       __u16 port;
> +
> +                       port = parse_arg_ul(argv[0], token, UINT16_MAX);
> +                       err = bpf_map_update_elem(ports_map_fd, &port_idx, &port, BPF_ANY);
> +                       if (err != 0) {
> +                               fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err));
> +                               fprintf(stderr, "Failed to add port %u (index %u)\n",
> +                                       port, port_idx);
> +                               goto out_close_maps;
> +                       }
> +                       fprintf(stderr, "Added port %u\n", port);
> +                       port_idx++;
> +               }
> +               err = bpf_map_update_elem(ports_map_fd, &port_idx, &port_last, BPF_ANY);
> +               if (err != 0) {
> +                       fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err));
> +                       fprintf(stderr, "Failed to add the terminator value 0 (index %u)\n",
> +                               port_idx);
> +                       goto out_close_maps;
> +               }
> +       }
> +
> +       if (tcpipopts) {
> +               __u32 key = 0;
> +
> +               fprintf(stderr, "Replacing TCP/IP options\n");
> +
> +               err = bpf_map_update_elem(values_map_fd, &key, &tcpipopts, BPF_ANY);
> +               if (err != 0) {
> +                       fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err));
> +                       goto out_close_maps;
> +               }
> +       }
> +
> +       if ((ports || tcpipopts) && attached_prog_id == 0 && !single)
> +               goto out_close_maps;
> +
> +       prevcnt = 0;
> +       firstiter = true;
> +       while (true) {
> +               __u32 key = 1;
> +               __u64 value;
> +
> +               err = bpf_map_lookup_elem(values_map_fd, &key, &value);
> +               if (err != 0) {
> +                       fprintf(stderr, "Error: bpf_map_lookup_elem: %s\n", strerror(-err));
> +                       goto out_close_maps;
> +               }
> +               if (firstiter) {
> +                       prevcnt = value;
> +                       firstiter = false;
> +               }
> +               if (single) {
> +                       printf("Total SYNACKs generated: %llu\n", value);
> +                       break;
> +               }
> +               printf("SYNACKs generated: %llu (total %llu)\n", value - prevcnt, value);
> +               prevcnt = value;
> +               sleep(1);
> +       }
> +
> +out_close_maps:
> +       close(values_map_fd);
> +       close(ports_map_fd);
> +out:
> +       return err == 0 ? 0 : 1;
> +}
> --
> 2.30.2
>

Patch

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 595565eb68c0..ca2f47f45670 100644
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -43,3 +43,4 @@  test_cpp
 *.tmp
 xdpxceiver
 xdp_redirect_multi
+xdp_synproxy
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 8ad7a733a505..e4ce21f4a474 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -82,7 +82,7 @@  TEST_PROGS_EXTENDED := with_addr.sh \
 TEST_GEN_PROGS_EXTENDED = test_sock_addr test_skb_cgroup_id_user \
 	flow_dissector_load test_flow_dissector test_tcp_check_syncookie_user \
 	test_lirc_mode2_user xdping test_cpp runqslower bench bpf_testmod.ko \
-	xdpxceiver xdp_redirect_multi
+	xdpxceiver xdp_redirect_multi xdp_synproxy
 
 TEST_CUSTOM_PROGS = $(OUTPUT)/urandom_read
 
@@ -502,6 +502,7 @@  TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
 			 cap_helpers.c
 TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
 		       $(OUTPUT)/liburandom_read.so			\
+		       $(OUTPUT)/xdp_synproxy				\
 		       ima_setup.sh					\
 		       $(wildcard progs/btf_dump_test_case_*.c)
 TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c b/tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c
new file mode 100644
index 000000000000..d9ee884c2a2b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_synproxy.c
@@ -0,0 +1,146 @@ 
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
+
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <ctype.h>
+
+#define CMD_OUT_BUF_SIZE 1023
+
+#define SYS(cmd) ({ \
+	if (!ASSERT_OK(system(cmd), (cmd))) \
+		goto out; \
+})
+
+#define SYS_OUT(cmd) ({ \
+	FILE *f = popen((cmd), "r"); \
+	if (!ASSERT_OK_PTR(f, (cmd))) \
+		goto out; \
+	f; \
+})
+
+/* out must be at least `size * 4 + 1` bytes long */
+static void escape_str(char *out, const char *in, size_t size)
+{
+	static const char *hex = "0123456789ABCDEF";
+	size_t i;
+
+	for (i = 0; i < size; i++) {
+		if (isprint(in[i]) && in[i] != '\\' && in[i] != '\'') {
+			*out++ = in[i];
+		} else {
+			*out++ = '\\';
+			*out++ = 'x';
+			*out++ = hex[(in[i] >> 4) & 0xf];
+			*out++ = hex[in[i] & 0xf];
+		}
+	}
+	*out++ = '\0';
+}
+
+static bool expect_str(char *buf, size_t size, const char *str, const char *name)
+{
+	static char escbuf_expected[CMD_OUT_BUF_SIZE * 4];
+	static char escbuf_actual[CMD_OUT_BUF_SIZE * 4];
+	static int duration = 0;
+	bool ok;
+
+	ok = size == strlen(str) && !memcmp(buf, str, size);
+
+	if (!ok) {
+		escape_str(escbuf_expected, str, strlen(str));
+		escape_str(escbuf_actual, buf, size);
+	}
+	CHECK(!ok, name, "unexpected %s: actual '%s' != expected '%s'\n",
+	      name, escbuf_actual, escbuf_expected);
+
+	return ok;
+}
+
+void test_xdp_synproxy(void)
+{
+	int server_fd = -1, client_fd = -1, accept_fd = -1;
+	struct nstoken *ns = NULL;
+	FILE *ctrl_file = NULL;
+	char buf[CMD_OUT_BUF_SIZE];
+	size_t size;
+
+	SYS("ip netns add synproxy");
+
+	SYS("ip link add tmp0 type veth peer name tmp1");
+	SYS("ip link set tmp1 netns synproxy");
+	SYS("ip link set tmp0 up");
+	SYS("ip addr replace 198.18.0.1/24 dev tmp0");
+
+	/* When checksum offload is enabled, the XDP program sees wrong
+	 * checksums and drops packets.
+	 */
+	SYS("ethtool -K tmp0 tx off");
+	/* Workaround required for veth. */
+	SYS("ip link set tmp0 xdp object xdp_dummy.o section xdp 2> /dev/null");
+
+	ns = open_netns("synproxy");
+	if (!ASSERT_OK_PTR(ns, "setns"))
+		goto out;
+
+	SYS("ip link set lo up");
+	SYS("ip link set tmp1 up");
+	SYS("ip addr replace 198.18.0.2/24 dev tmp1");
+	SYS("sysctl -w net.ipv4.tcp_syncookies=2");
+	SYS("sysctl -w net.ipv4.tcp_timestamps=1");
+	SYS("sysctl -w net.netfilter.nf_conntrack_tcp_loose=0");
+	SYS("iptables -t raw -I PREROUTING \
+	    -i tmp1 -p tcp -m tcp --syn --dport 8080 -j CT --notrack");
+	SYS("iptables -t filter -A INPUT \
+	    -i tmp1 -p tcp -m tcp --dport 8080 -m state --state INVALID,UNTRACKED \
+	    -j SYNPROXY --sack-perm --timestamp --wscale 7 --mss 1460");
+	SYS("iptables -t filter -A INPUT \
+	    -i tmp1 -m state --state INVALID -j DROP");
+
+	ctrl_file = SYS_OUT("./xdp_synproxy --iface tmp1 --ports 8080 --single \
+			    --mss4 1460 --mss6 1440 --wscale 7 --ttl 64");
+	size = fread(buf, 1, sizeof(buf), ctrl_file);
+	pclose(ctrl_file);
+	if (!expect_str(buf, size, "Total SYNACKs generated: 0\n",
+			"initial SYNACKs"))
+		goto out;
+
+	server_fd = start_server(AF_INET, SOCK_STREAM, "198.18.0.2", 8080, 0);
+	if (!ASSERT_GE(server_fd, 0, "start_server"))
+		goto out;
+
+	close_netns(ns);
+	ns = NULL;
+
+	client_fd = connect_to_fd(server_fd, 10000);
+	if (!ASSERT_GE(client_fd, 0, "connect_to_fd"))
+		goto out;
+
+	accept_fd = accept(server_fd, NULL, NULL);
+	if (!ASSERT_GE(accept_fd, 0, "accept"))
+		goto out;
+
+	ns = open_netns("synproxy");
+	if (!ASSERT_OK_PTR(ns, "setns"))
+		goto out;
+
+	ctrl_file = SYS_OUT("./xdp_synproxy --iface tmp1 --single");
+	size = fread(buf, 1, sizeof(buf), ctrl_file);
+	pclose(ctrl_file);
+	if (!expect_str(buf, size, "Total SYNACKs generated: 1\n",
+			"SYNACKs after connection"))
+		goto out;
+
+out:
+	if (accept_fd >= 0)
+		close(accept_fd);
+	if (client_fd >= 0)
+		close(client_fd);
+	if (server_fd >= 0)
+		close(server_fd);
+	if (ns)
+		close_netns(ns);
+
+	system("ip link del tmp0");
+	system("ip netns del synproxy");
+}
diff --git a/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c b/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
new file mode 100644
index 000000000000..53b9865276a4
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/xdp_synproxy_kern.c
@@ -0,0 +1,763 @@ 
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+#include <asm/errno.h>
+
+#define NSEC_PER_SEC 1000000000L
+
+#define ETH_ALEN 6
+#define ETH_P_IP 0x0800
+#define ETH_P_IPV6 0x86DD
+
+#define tcp_flag_word(tp) (((union tcp_word_hdr *)(tp))->words[3])
+
+#define IP_DF 0x4000
+#define IP_MF 0x2000
+#define IP_OFFSET 0x1fff
+
+#define NEXTHDR_TCP 6
+
+#define TCPOPT_NOP 1
+#define TCPOPT_EOL 0
+#define TCPOPT_MSS 2
+#define TCPOPT_WINDOW 3
+#define TCPOPT_SACK_PERM 4
+#define TCPOPT_TIMESTAMP 8
+
+#define TCPOLEN_MSS 4
+#define TCPOLEN_WINDOW 3
+#define TCPOLEN_SACK_PERM 2
+#define TCPOLEN_TIMESTAMP 10
+
+#define TCP_TS_HZ 1000
+#define TS_OPT_WSCALE_MASK 0xf
+#define TS_OPT_SACK (1 << 4)
+#define TS_OPT_ECN (1 << 5)
+#define TSBITS 6
+#define TSMASK (((__u32)1 << TSBITS) - 1)
+#define TCP_MAX_WSCALE 14U
+
+#define IPV4_MAXLEN 60
+#define TCP_MAXLEN 60
+
+#define DEFAULT_MSS4 1460
+#define DEFAULT_MSS6 1440
+#define DEFAULT_WSCALE 7
+#define DEFAULT_TTL 64
+#define MAX_ALLOWED_PORTS 8
+
+#define swap(a, b) \
+	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
+
+#define __get_unaligned_t(type, ptr) ({						\
+	const struct { type x; } __attribute__((__packed__)) *__pptr = (typeof(__pptr))(ptr); \
+	__pptr->x;								\
+})
+
+#define get_unaligned(ptr) __get_unaligned_t(typeof(*(ptr)), (ptr))
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(max_entries, 2);
+} values SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, __u32);
+	__type(value, __u16);
+	__uint(max_entries, MAX_ALLOWED_PORTS);
+} allowed_ports SEC(".maps");
+
+extern struct nf_conn *bpf_xdp_ct_lookup(struct xdp_md *xdp_ctx,
+					 struct bpf_sock_tuple *bpf_tuple,
+					 __u32 len_tuple,
+					 struct bpf_ct_opts *opts,
+					 __u32 len_opts) __ksym;
+
+extern void bpf_ct_release(struct nf_conn *ct) __ksym;
+
+static __always_inline void swap_eth_addr(__u8 *a, __u8 *b)
+{
+	__u8 tmp[ETH_ALEN];
+
+	__builtin_memcpy(tmp, a, ETH_ALEN);
+	__builtin_memcpy(a, b, ETH_ALEN);
+	__builtin_memcpy(b, tmp, ETH_ALEN);
+}
+
+static __always_inline __u16 csum_fold(__u32 csum)
+{
+	csum = (csum & 0xffff) + (csum >> 16);
+	csum = (csum & 0xffff) + (csum >> 16);
+	return (__u16)~csum;
+}
+
+static __always_inline __u16 csum_tcpudp_magic(__be32 saddr, __be32 daddr,
+					       __u32 len, __u8 proto,
+					       __u32 csum)
+{
+	__u64 s = csum;
+
+	s += (__u32)saddr;
+	s += (__u32)daddr;
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	s += proto + len;
+#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	s += (proto + len) << 8;
+#else
+#error Unknown endian
+#endif
+	s = (s & 0xffffffff) + (s >> 32);
+	s = (s & 0xffffffff) + (s >> 32);
+
+	return csum_fold((__u32)s);
+}
+
+static __always_inline __u16 csum_ipv6_magic(const struct in6_addr *saddr,
+					     const struct in6_addr *daddr,
+					     __u32 len, __u8 proto, __u32 csum)
+{
+	__u64 sum = csum;
+	int i;
+
+#pragma unroll
+	for (i = 0; i < 4; i++)
+		sum += (__u32)saddr->in6_u.u6_addr32[i];
+
+#pragma unroll
+	for (i = 0; i < 4; i++)
+		sum += (__u32)daddr->in6_u.u6_addr32[i];
+
+	/* Don't combine additions to avoid 32-bit overflow. */
+	sum += bpf_htonl(len);
+	sum += bpf_htonl(proto);
+
+	sum = (sum & 0xffffffff) + (sum >> 32);
+	sum = (sum & 0xffffffff) + (sum >> 32);
+
+	return csum_fold((__u32)sum);
+}
+
+static __always_inline __u64 tcp_clock_ns(void)
+{
+	return bpf_ktime_get_ns();
+}
+
+static __always_inline __u32 tcp_ns_to_ts(__u64 ns)
+{
+	return ns / (NSEC_PER_SEC / TCP_TS_HZ);
+}
+
+static __always_inline __u32 tcp_time_stamp_raw(void)
+{
+	return tcp_ns_to_ts(tcp_clock_ns());
+}
+
+struct tcpopt_context {
+	__u8 *ptr;
+	__u8 *end;
+	void *data_end;
+	__be32 *tsecr;
+	__u8 wscale;
+	bool option_timestamp;
+	bool option_sack;
+};
+
+static int tscookie_tcpopt_parse(struct tcpopt_context *ctx)
+{
+	__u8 opcode, opsize;
+
+	if (ctx->ptr >= ctx->end)
+		return 1;
+	if (ctx->ptr >= ctx->data_end)
+		return 1;
+
+	opcode = ctx->ptr[0];
+
+	if (opcode == TCPOPT_EOL)
+		return 1;
+	if (opcode == TCPOPT_NOP) {
+		++ctx->ptr;
+		return 0;
+	}
+
+	if (ctx->ptr + 1 >= ctx->end)
+		return 1;
+	if (ctx->ptr + 1 >= ctx->data_end)
+		return 1;
+	opsize = ctx->ptr[1];
+	if (opsize < 2)
+		return 1;
+
+	if (ctx->ptr + opsize > ctx->end)
+		return 1;
+
+	switch (opcode) {
+	case TCPOPT_WINDOW:
+		if (opsize == TCPOLEN_WINDOW && ctx->ptr + TCPOLEN_WINDOW <= ctx->data_end)
+			ctx->wscale = ctx->ptr[2] < TCP_MAX_WSCALE ? ctx->ptr[2] : TCP_MAX_WSCALE;
+		break;
+	case TCPOPT_TIMESTAMP:
+		if (opsize == TCPOLEN_TIMESTAMP && ctx->ptr + TCPOLEN_TIMESTAMP <= ctx->data_end) {
+			ctx->option_timestamp = true;
+			/* Client's tsval becomes our tsecr. */
+			*ctx->tsecr = get_unaligned((__be32 *)(ctx->ptr + 2));
+		}
+		break;
+	case TCPOPT_SACK_PERM:
+		if (opsize == TCPOLEN_SACK_PERM)
+			ctx->option_sack = true;
+		break;
+	}
+
+	ctx->ptr += opsize;
+
+	return 0;
+}
+
+static int tscookie_tcpopt_parse_batch(__u32 index, void *context)
+{
+	int i;
+
+	for (i = 0; i < 7; i++)
+		if (tscookie_tcpopt_parse(context))
+			return 1;
+	return 0;
+}
+
+static __always_inline bool tscookie_init(struct tcphdr *tcp_header,
+					  __u16 tcp_len, __be32 *tsval,
+					  __be32 *tsecr, void *data_end)
+{
+	struct tcpopt_context loop_ctx = {
+		.ptr = (__u8 *)(tcp_header + 1),
+		.end = (__u8 *)tcp_header + tcp_len,
+		.data_end = data_end,
+		.tsecr = tsecr,
+		.wscale = TS_OPT_WSCALE_MASK,
+		.option_timestamp = false,
+		.option_sack = false,
+	};
+	u32 cookie;
+
+	bpf_loop(6, tscookie_tcpopt_parse_batch, &loop_ctx, 0);
+
+	if (!loop_ctx.option_timestamp)
+		return false;
+
+	cookie = tcp_time_stamp_raw() & ~TSMASK;
+	cookie |= loop_ctx.wscale & TS_OPT_WSCALE_MASK;
+	if (loop_ctx.option_sack)
+		cookie |= TS_OPT_SACK;
+	if (tcp_header->ece && tcp_header->cwr)
+		cookie |= TS_OPT_ECN;
+	*tsval = bpf_htonl(cookie);
+
+	return true;
+}
+
+static __always_inline void values_get_tcpipopts(__u16 *mss, __u8 *wscale,
+						 __u8 *ttl, bool ipv6)
+{
+	__u32 key = 0;
+	__u64 *value;
+
+	value = bpf_map_lookup_elem(&values, &key);
+	if (value && *value != 0) {
+		if (ipv6)
+			*mss = (*value >> 32) & 0xffff;
+		else
+			*mss = *value & 0xffff;
+		*wscale = (*value >> 16) & 0xf;
+		*ttl = (*value >> 24) & 0xff;
+		return;
+	}
+
+	*mss = ipv6 ? DEFAULT_MSS6 : DEFAULT_MSS4;
+	*wscale = DEFAULT_WSCALE;
+	*ttl = DEFAULT_TTL;
+}
+
+static __always_inline void values_inc_synacks(void)
+{
+	__u32 key = 1;
+	__u32 *value;
+
+	value = bpf_map_lookup_elem(&values, &key);
+	if (value)
+		__sync_fetch_and_add(value, 1);
+}
+
+static __always_inline bool check_port_allowed(__u16 port)
+{
+	__u32 i;
+
+	for (i = 0; i < MAX_ALLOWED_PORTS; i++) {
+		__u32 key = i;
+		__u16 *value;
+
+		value = bpf_map_lookup_elem(&allowed_ports, &key);
+
+		if (!value)
+			break;
+		/* 0 is a terminator value. Check it first to avoid matching on
+		 * a forbidden port == 0 and returning true.
+		 */
+		if (*value == 0)
+			break;
+
+		if (*value == port)
+			return true;
+	}
+
+	return false;
+}
+
+struct header_pointers {
+	struct ethhdr *eth;
+	struct iphdr *ipv4;
+	struct ipv6hdr *ipv6;
+	struct tcphdr *tcp;
+	__u16 tcp_len;
+};
+
+static __always_inline int tcp_dissect(void *data, void *data_end,
+				       struct header_pointers *hdr)
+{
+	hdr->eth = data;
+	if (hdr->eth + 1 > data_end)
+		return XDP_DROP;
+
+	switch (bpf_ntohs(hdr->eth->h_proto)) {
+	case ETH_P_IP:
+		hdr->ipv6 = NULL;
+
+		hdr->ipv4 = (void *)hdr->eth + sizeof(*hdr->eth);
+		if (hdr->ipv4 + 1 > data_end)
+			return XDP_DROP;
+		if (hdr->ipv4->ihl * 4 < sizeof(*hdr->ipv4))
+			return XDP_DROP;
+		if (hdr->ipv4->version != 4)
+			return XDP_DROP;
+
+		if (hdr->ipv4->protocol != IPPROTO_TCP)
+			return XDP_PASS;
+
+		hdr->tcp = (void *)hdr->ipv4 + hdr->ipv4->ihl * 4;
+		break;
+	case ETH_P_IPV6:
+		hdr->ipv4 = NULL;
+
+		hdr->ipv6 = (void *)hdr->eth + sizeof(*hdr->eth);
+		if (hdr->ipv6 + 1 > data_end)
+			return XDP_DROP;
+		if (hdr->ipv6->version != 6)
+			return XDP_DROP;
+
+		/* XXX: Extension headers are not supported and could circumvent
+		 * XDP SYN flood protection.
+		 */
+		if (hdr->ipv6->nexthdr != NEXTHDR_TCP)
+			return XDP_PASS;
+
+		hdr->tcp = (void *)hdr->ipv6 + sizeof(*hdr->ipv6);
+		break;
+	default:
+		/* XXX: VLANs will circumvent XDP SYN flood protection. */
+		return XDP_PASS;
+	}
+
+	if (hdr->tcp + 1 > data_end)
+		return XDP_DROP;
+	hdr->tcp_len = hdr->tcp->doff * 4;
+	if (hdr->tcp_len < sizeof(*hdr->tcp))
+		return XDP_DROP;
+
+	return XDP_TX;
+}
+
+static __always_inline int tcp_lookup(struct xdp_md *ctx, struct header_pointers *hdr)
+{
+	struct bpf_ct_opts ct_lookup_opts = {
+		.netns_id = BPF_F_CURRENT_NETNS,
+		.l4proto = IPPROTO_TCP,
+	};
+	struct bpf_sock_tuple tup = {};
+	struct nf_conn *ct;
+	__u32 tup_size;
+
+	if (hdr->ipv4) {
+		/* TCP doesn't normally use fragments, and XDP can't reassemble
+		 * them.
+		 */
+		if ((hdr->ipv4->frag_off & bpf_htons(IP_DF | IP_MF | IP_OFFSET)) != bpf_htons(IP_DF))
+			return XDP_DROP;
+
+		tup.ipv4.saddr = hdr->ipv4->saddr;
+		tup.ipv4.daddr = hdr->ipv4->daddr;
+		tup.ipv4.sport = hdr->tcp->source;
+		tup.ipv4.dport = hdr->tcp->dest;
+		tup_size = sizeof(tup.ipv4);
+	} else if (hdr->ipv6) {
+		__builtin_memcpy(tup.ipv6.saddr, &hdr->ipv6->saddr, sizeof(tup.ipv6.saddr));
+		__builtin_memcpy(tup.ipv6.daddr, &hdr->ipv6->daddr, sizeof(tup.ipv6.daddr));
+		tup.ipv6.sport = hdr->tcp->source;
+		tup.ipv6.dport = hdr->tcp->dest;
+		tup_size = sizeof(tup.ipv6);
+	} else {
+		/* The verifier can't track that either ipv4 or ipv6 is not
+		 * NULL.
+		 */
+		return XDP_ABORTED;
+	}
+	ct = bpf_xdp_ct_lookup(ctx, &tup, tup_size, &ct_lookup_opts, sizeof(ct_lookup_opts));
+	if (ct) {
+		unsigned long status = ct->status;
+
+		bpf_ct_release(ct);
+		if (status & IPS_CONFIRMED_BIT)
+			return XDP_PASS;
+	} else if (ct_lookup_opts.error != -ENOENT) {
+		return XDP_ABORTED;
+	}
+
+	/* error == -ENOENT || !(status & IPS_CONFIRMED_BIT) */
+	return XDP_TX;
+}
+
+static __always_inline __u8 tcp_mkoptions(__be32 *buf, __be32 *tsopt, __u16 mss,
+					  __u8 wscale)
+{
+	__be32 *start = buf;
+
+	*buf++ = bpf_htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | mss);
+
+	if (!tsopt)
+		return buf - start;
+
+	if (tsopt[0] & bpf_htonl(1 << 4))
+		*buf++ = bpf_htonl((TCPOPT_SACK_PERM << 24) |
+				   (TCPOLEN_SACK_PERM << 16) |
+				   (TCPOPT_TIMESTAMP << 8) |
+				   TCPOLEN_TIMESTAMP);
+	else
+		*buf++ = bpf_htonl((TCPOPT_NOP << 24) |
+				   (TCPOPT_NOP << 16) |
+				   (TCPOPT_TIMESTAMP << 8) |
+				   TCPOLEN_TIMESTAMP);
+	*buf++ = tsopt[0];
+	*buf++ = tsopt[1];
+
+	if ((tsopt[0] & bpf_htonl(0xf)) != bpf_htonl(0xf))
+		*buf++ = bpf_htonl((TCPOPT_NOP << 24) |
+				   (TCPOPT_WINDOW << 16) |
+				   (TCPOLEN_WINDOW << 8) |
+				   wscale);
+
+	return buf - start;
+}
+
+static __always_inline void tcp_gen_synack(struct tcphdr *tcp_header,
+					   __u32 cookie, __be32 *tsopt,
+					   __u16 mss, __u8 wscale)
+{
+	void *tcp_options;
+
+	tcp_flag_word(tcp_header) = TCP_FLAG_SYN | TCP_FLAG_ACK;
+	if (tsopt && (tsopt[0] & bpf_htonl(1 << 5)))
+		tcp_flag_word(tcp_header) |= TCP_FLAG_ECE;
+	tcp_header->doff = 5; /* doff is part of tcp_flag_word. */
+	swap(tcp_header->source, tcp_header->dest);
+	tcp_header->ack_seq = bpf_htonl(bpf_ntohl(tcp_header->seq) + 1);
+	tcp_header->seq = bpf_htonl(cookie);
+	tcp_header->window = 0;
+	tcp_header->urg_ptr = 0;
+	tcp_header->check = 0; /* Calculate checksum later. */
+
+	tcp_options = (void *)(tcp_header + 1);
+	tcp_header->doff += tcp_mkoptions(tcp_options, tsopt, mss, wscale);
+}
+
+static __always_inline void tcpv4_gen_synack(struct header_pointers *hdr,
+					     __u32 cookie, __be32 *tsopt)
+{
+	__u8 wscale;
+	__u16 mss;
+	__u8 ttl;
+
+	values_get_tcpipopts(&mss, &wscale, &ttl, false);
+
+	swap_eth_addr(hdr->eth->h_source, hdr->eth->h_dest);
+
+	swap(hdr->ipv4->saddr, hdr->ipv4->daddr);
+	hdr->ipv4->check = 0; /* Calculate checksum later. */
+	hdr->ipv4->tos = 0;
+	hdr->ipv4->id = 0;
+	hdr->ipv4->ttl = ttl;
+
+	tcp_gen_synack(hdr->tcp, cookie, tsopt, mss, wscale);
+
+	hdr->tcp_len = hdr->tcp->doff * 4;
+	hdr->ipv4->tot_len = bpf_htons(sizeof(*hdr->ipv4) + hdr->tcp_len);
+}
+
+static __always_inline void tcpv6_gen_synack(struct header_pointers *hdr,
+					     __u32 cookie, __be32 *tsopt)
+{
+	__u8 wscale;
+	__u16 mss;
+	__u8 ttl;
+
+	values_get_tcpipopts(&mss, &wscale, &ttl, true);
+
+	swap_eth_addr(hdr->eth->h_source, hdr->eth->h_dest);
+
+	swap(hdr->ipv6->saddr, hdr->ipv6->daddr);
+	*(__be32 *)hdr->ipv6 = bpf_htonl(0x60000000);
+	hdr->ipv6->hop_limit = ttl;
+
+	tcp_gen_synack(hdr->tcp, cookie, tsopt, mss, wscale);
+
+	hdr->tcp_len = hdr->tcp->doff * 4;
+	hdr->ipv6->payload_len = bpf_htons(hdr->tcp_len);
+}
+
+static __always_inline int syncookie_handle_syn(struct header_pointers *hdr,
+						struct xdp_md *ctx,
+						void *data, void *data_end)
+{
+	__u32 old_pkt_size, new_pkt_size;
+	/* Unlike clang 10, clang 11 and 12 generate code that doesn't pass the
+	 * BPF verifier if tsopt is not volatile. Volatile forces it to store
+	 * the pointer value and use it directly, otherwise tcp_mkoptions is
+	 * (mis)compiled like this:
+	 *   if (!tsopt)
+	 *       return buf - start;
+	 *   reg = stored_return_value_of_tscookie_init;
+	 *   if (reg)
+	 *       tsopt = tsopt_buf;
+	 *   else
+	 *       tsopt = NULL;
+	 *   ...
+	 *   *buf++ = tsopt[1];
+	 * It creates a dead branch where tsopt is assigned NULL, but the
+	 * verifier can't prove it's dead and blocks the program.
+	 */
+	__be32 * volatile tsopt = NULL;
+	__be32 tsopt_buf[2] = {};
+	__u16 ip_len;
+	__u32 cookie;
+	__s64 value;
+
+	/* Checksum is not yet verified, but both checksum failure and TCP
+	 * header checks return XDP_DROP, so the order doesn't matter.
+	 */
+	if (hdr->tcp->fin || hdr->tcp->rst)
+		return XDP_DROP;
+
+	/* Issue SYN cookies on allowed ports, drop SYN packets on blocked
+	 * ports.
+	 */
+	if (!check_port_allowed(bpf_ntohs(hdr->tcp->dest)))
+		return XDP_DROP;
+
+	if (hdr->ipv4) {
+		/* Check the IPv4 and TCP checksums before creating a SYNACK. */
+		value = bpf_csum_diff(0, 0, (void *)hdr->ipv4, hdr->ipv4->ihl * 4, 0);
+		if (value < 0)
+			return XDP_ABORTED;
+		if (csum_fold(value) != 0)
+			return XDP_DROP; /* Bad IPv4 checksum. */
+
+		value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
+		if (value < 0)
+			return XDP_ABORTED;
+		if (csum_tcpudp_magic(hdr->ipv4->saddr, hdr->ipv4->daddr,
+				      hdr->tcp_len, IPPROTO_TCP, value) != 0)
+			return XDP_DROP; /* Bad TCP checksum. */
+
+		ip_len = sizeof(*hdr->ipv4);
+
+		value = bpf_tcp_raw_gen_syncookie_ipv4(hdr->ipv4, hdr->tcp,
+						       hdr->tcp_len);
+	} else if (hdr->ipv6) {
+		/* Check the TCP checksum before creating a SYNACK. */
+		value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
+		if (value < 0)
+			return XDP_ABORTED;
+		if (csum_ipv6_magic(&hdr->ipv6->saddr, &hdr->ipv6->daddr,
+				    hdr->tcp_len, IPPROTO_TCP, value) != 0)
+			return XDP_DROP; /* Bad TCP checksum. */
+
+		ip_len = sizeof(*hdr->ipv6);
+
+		value = bpf_tcp_raw_gen_syncookie_ipv6(hdr->ipv6, hdr->tcp,
+						       hdr->tcp_len);
+	} else {
+		return XDP_ABORTED;
+	}
+
+	if (value < 0)
+		return XDP_ABORTED;
+	cookie = (__u32)value;
+
+	if (tscookie_init((void *)hdr->tcp, hdr->tcp_len,
+			  &tsopt_buf[0], &tsopt_buf[1], data_end))
+		tsopt = tsopt_buf;
+
+	/* Check that there is enough space for a SYNACK. It also covers
+	 * the check that the destination of the __builtin_memmove below
+	 * doesn't overflow.
+	 */
+	if (data + sizeof(*hdr->eth) + ip_len + TCP_MAXLEN > data_end)
+		return XDP_ABORTED;
+
+	if (hdr->ipv4) {
+		if (hdr->ipv4->ihl * 4 > sizeof(*hdr->ipv4)) {
+			struct tcphdr *new_tcp_header;
+
+			new_tcp_header = data + sizeof(*hdr->eth) + sizeof(*hdr->ipv4);
+			__builtin_memmove(new_tcp_header, hdr->tcp, sizeof(*hdr->tcp));
+			hdr->tcp = new_tcp_header;
+
+			hdr->ipv4->ihl = sizeof(*hdr->ipv4) / 4;
+		}
+
+		tcpv4_gen_synack(hdr, cookie, tsopt);
+	} else if (hdr->ipv6) {
+		tcpv6_gen_synack(hdr, cookie, tsopt);
+	} else {
+		return XDP_ABORTED;
+	}
+
+	/* Recalculate checksums. */
+	hdr->tcp->check = 0;
+	value = bpf_csum_diff(0, 0, (void *)hdr->tcp, hdr->tcp_len, 0);
+	if (value < 0)
+		return XDP_ABORTED;
+	if (hdr->ipv4) {
+		hdr->tcp->check = csum_tcpudp_magic(hdr->ipv4->saddr,
+						    hdr->ipv4->daddr,
+						    hdr->tcp_len,
+						    IPPROTO_TCP,
+						    value);
+
+		hdr->ipv4->check = 0;
+		value = bpf_csum_diff(0, 0, (void *)hdr->ipv4, sizeof(*hdr->ipv4), 0);
+		if (value < 0)
+			return XDP_ABORTED;
+		hdr->ipv4->check = csum_fold(value);
+	} else if (hdr->ipv6) {
+		hdr->tcp->check = csum_ipv6_magic(&hdr->ipv6->saddr,
+						  &hdr->ipv6->daddr,
+						  hdr->tcp_len,
+						  IPPROTO_TCP,
+						  value);
+	} else {
+		return XDP_ABORTED;
+	}
+
+	/* Set the new packet size. */
+	old_pkt_size = data_end - data;
+	new_pkt_size = sizeof(*hdr->eth) + ip_len + hdr->tcp->doff * 4;
+	if (bpf_xdp_adjust_tail(ctx, new_pkt_size - old_pkt_size))
+		return XDP_ABORTED;
+
+	values_inc_synacks();
+
+	return XDP_TX;
+}
+
+static __always_inline int syncookie_handle_ack(struct header_pointers *hdr)
+{
+	int err;
+
+	if (hdr->tcp->rst)
+		return XDP_DROP;
+
+	if (hdr->ipv4)
+		err = bpf_tcp_raw_check_syncookie_ipv4(hdr->ipv4, hdr->tcp);
+	else if (hdr->ipv6)
+		err = bpf_tcp_raw_check_syncookie_ipv6(hdr->ipv6, hdr->tcp);
+	else
+		return XDP_ABORTED;
+	if (err)
+		return XDP_DROP;
+
+	return XDP_PASS;
+}
+
+SEC("xdp")
+int syncookie_xdp(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	struct header_pointers hdr;
+	__s64 value;
+	int ret;
+
+	struct bpf_ct_opts ct_lookup_opts = {
+		.netns_id = BPF_F_CURRENT_NETNS,
+		.l4proto = IPPROTO_TCP,
+	};
+
+	ret = tcp_dissect(data, data_end, &hdr);
+	if (ret != XDP_TX)
+		return ret;
+
+	ret = tcp_lookup(ctx, &hdr);
+	if (ret != XDP_TX)
+		return ret;
+
+	/* Packet is TCP and doesn't belong to an established connection. */
+
+	if ((hdr.tcp->syn ^ hdr.tcp->ack) != 1)
+		return XDP_DROP;
+
+	/* Grow the TCP header to TCP_MAXLEN to be able to pass any hdr.tcp_len
+	 * to bpf_tcp_raw_gen_syncookie_ipv{4,6} and pass the verifier.
+	 */
+	if (bpf_xdp_adjust_tail(ctx, TCP_MAXLEN - hdr.tcp_len))
+		return XDP_ABORTED;
+
+	data_end = (void *)(long)ctx->data_end;
+	data = (void *)(long)ctx->data;
+
+	if (hdr.ipv4) {
+		hdr.eth = data;
+		hdr.ipv4 = (void *)hdr.eth + sizeof(*hdr.eth);
+		/* IPV4_MAXLEN is needed when calculating checksum.
+		 * At least sizeof(struct iphdr) is needed here to access ihl.
+		 */
+		if ((void *)hdr.ipv4 + IPV4_MAXLEN > data_end)
+			return XDP_ABORTED;
+		hdr.tcp = (void *)hdr.ipv4 + hdr.ipv4->ihl * 4;
+	} else if (hdr.ipv6) {
+		hdr.eth = data;
+		hdr.ipv6 = (void *)hdr.eth + sizeof(*hdr.eth);
+		hdr.tcp = (void *)hdr.ipv6 + sizeof(*hdr.ipv6);
+	} else {
+		return XDP_ABORTED;
+	}
+
+	if ((void *)hdr.tcp + TCP_MAXLEN > data_end)
+		return XDP_ABORTED;
+
+	/* We run out of registers, tcp_len gets spilled to the stack, and the
+	 * verifier forgets its min and max values checked above in tcp_dissect.
+	 */
+	hdr.tcp_len = hdr.tcp->doff * 4;
+	if (hdr.tcp_len < sizeof(*hdr.tcp))
+		return XDP_ABORTED;
+
+	return hdr.tcp->syn ? syncookie_handle_syn(&hdr, ctx, data, data_end) :
+			      syncookie_handle_ack(&hdr);
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/xdp_synproxy.c b/tools/testing/selftests/bpf/xdp_synproxy.c
new file mode 100644
index 000000000000..4653d4655b5f
--- /dev/null
+++ b/tools/testing/selftests/bpf/xdp_synproxy.c
@@ -0,0 +1,418 @@ 
+// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
+/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
+
+#include <stdnoreturn.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <getopt.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+#include <net/if.h>
+#include <linux/if_link.h>
+#include <linux/limits.h>
+
+static unsigned int ifindex;
+static __u32 attached_prog_id;
+
+static void noreturn cleanup(int sig)
+{
+	DECLARE_LIBBPF_OPTS(bpf_xdp_attach_opts, opts);
+	int prog_fd;
+	int err;
+
+	if (attached_prog_id == 0)
+		exit(0);
+
+	prog_fd = bpf_prog_get_fd_by_id(attached_prog_id);
+	if (prog_fd < 0) {
+		fprintf(stderr, "Error: bpf_prog_get_fd_by_id: %s\n", strerror(-prog_fd));
+		err = bpf_xdp_attach(ifindex, -1, 0, NULL);
+		if (err < 0) {
+			fprintf(stderr, "Error: bpf_set_link_xdp_fd: %s\n", strerror(-err));
+			fprintf(stderr, "Failed to detach XDP program\n");
+			exit(1);
+		}
+	} else {
+		opts.old_prog_fd = prog_fd;
+		err = bpf_xdp_attach(ifindex, -1, XDP_FLAGS_REPLACE, &opts);
+		close(prog_fd);
+		if (err < 0) {
+			fprintf(stderr, "Error: bpf_set_link_xdp_fd_opts: %s\n", strerror(-err));
+			/* Not an error if already replaced by someone else. */
+			if (err != -EEXIST) {
+				fprintf(stderr, "Failed to detach XDP program\n");
+				exit(1);
+			}
+		}
+	}
+	exit(0);
+}
+
+static noreturn void usage(const char *progname)
+{
+	fprintf(stderr, "Usage: %s [--iface <iface>|--prog <prog_id>] [--mss4 <mss ipv4> --mss6 <mss ipv6> --wscale <wscale> --ttl <ttl>] [--ports <port1>,<port2>,...] [--single]\n",
+		progname);
+	exit(1);
+}
+
+static unsigned long parse_arg_ul(const char *progname, const char *arg, unsigned long limit)
+{
+	unsigned long res;
+	char *endptr;
+
+	errno = 0;
+	res = strtoul(arg, &endptr, 10);
+	if (errno != 0 || *endptr != '\0' || arg[0] == '\0' || res > limit)
+		usage(progname);
+
+	return res;
+}
+
+static void parse_options(int argc, char *argv[], unsigned int *ifindex, __u32 *prog_id,
+			  __u64 *tcpipopts, char **ports, bool *single)
+{
+	static struct option long_options[] = {
+		{ "help", no_argument, NULL, 'h' },
+		{ "iface", required_argument, NULL, 'i' },
+		{ "prog", required_argument, NULL, 'x' },
+		{ "mss4", required_argument, NULL, 4 },
+		{ "mss6", required_argument, NULL, 6 },
+		{ "wscale", required_argument, NULL, 'w' },
+		{ "ttl", required_argument, NULL, 't' },
+		{ "ports", required_argument, NULL, 'p' },
+		{ "single", no_argument, NULL, 's' },
+		{ NULL, 0, NULL, 0 },
+	};
+	unsigned long mss4, mss6, wscale, ttl;
+	unsigned int tcpipopts_mask = 0;
+
+	if (argc < 2)
+		usage(argv[0]);
+
+	*ifindex = 0;
+	*prog_id = 0;
+	*tcpipopts = 0;
+	*ports = NULL;
+	*single = false;
+
+	while (true) {
+		int opt;
+
+		opt = getopt_long(argc, argv, "", long_options, NULL);
+		if (opt == -1)
+			break;
+
+		switch (opt) {
+		case 'h':
+			usage(argv[0]);
+			break;
+		case 'i':
+			*ifindex = if_nametoindex(optarg);
+			if (*ifindex == 0)
+				usage(argv[0]);
+			break;
+		case 'x':
+			*prog_id = parse_arg_ul(argv[0], optarg, UINT32_MAX);
+			if (*prog_id == 0)
+				usage(argv[0]);
+			break;
+		case 4:
+			mss4 = parse_arg_ul(argv[0], optarg, UINT16_MAX);
+			tcpipopts_mask |= 1 << 0;
+			break;
+		case 6:
+			mss6 = parse_arg_ul(argv[0], optarg, UINT16_MAX);
+			tcpipopts_mask |= 1 << 1;
+			break;
+		case 'w':
+			wscale = parse_arg_ul(argv[0], optarg, 14);
+			tcpipopts_mask |= 1 << 2;
+			break;
+		case 't':
+			ttl = parse_arg_ul(argv[0], optarg, UINT8_MAX);
+			tcpipopts_mask |= 1 << 3;
+			break;
+		case 'p':
+			*ports = optarg;
+			break;
+		case 's':
+			*single = true;
+			break;
+		default:
+			usage(argv[0]);
+		}
+	}
+	if (optind < argc)
+		usage(argv[0]);
+
+	if (tcpipopts_mask == 0xf) {
+		if (mss4 == 0 || mss6 == 0 || wscale == 0 || ttl == 0)
+			usage(argv[0]);
+		*tcpipopts = (mss6 << 32) | (ttl << 24) | (wscale << 16) | mss4;
+	} else if (tcpipopts_mask != 0) {
+		usage(argv[0]);
+	}
+
+	if (*ifindex != 0 && *prog_id != 0)
+		usage(argv[0]);
+	if (*ifindex == 0 && *prog_id == 0)
+		usage(argv[0]);
+}
+
+static int syncookie_attach(const char *argv0, unsigned int ifindex)
+{
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
+	char xdp_filename[PATH_MAX];
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	int prog_fd;
+	int err;
+
+	snprintf(xdp_filename, sizeof(xdp_filename), "%s_kern.o", argv0);
+	obj = bpf_object__open_file(xdp_filename, NULL);
+	err = libbpf_get_error(obj);
+	if (err < 0) {
+		fprintf(stderr, "Error: bpf_object__open_file: %s\n", strerror(-err));
+		return err;
+	}
+
+	err = bpf_object__load(obj);
+	if (err < 0) {
+		fprintf(stderr, "Error: bpf_object__open_file: %s\n", strerror(-err));
+		return err;
+	}
+
+	prog = bpf_object__find_program_by_name(obj, "syncookie_xdp");
+	if (!prog) {
+		fprintf(stderr, "Error: bpf_object__find_program_by_name: program syncookie_xdp was not found\n");
+		return -ENOENT;
+	}
+
+	prog_fd = bpf_program__fd(prog);
+
+	err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
+	if (err < 0) {
+		fprintf(stderr, "Error: bpf_obj_get_info_by_fd: %s\n", strerror(-err));
+		goto out;
+	}
+	attached_prog_id = info.id;
+	signal(SIGINT, cleanup);
+	signal(SIGTERM, cleanup);
+	err = bpf_xdp_attach(ifindex, prog_fd, XDP_FLAGS_UPDATE_IF_NOEXIST, NULL);
+	if (err < 0) {
+		fprintf(stderr, "Error: bpf_set_link_xdp_fd: %s\n", strerror(-err));
+		signal(SIGINT, SIG_DFL);
+		signal(SIGTERM, SIG_DFL);
+		attached_prog_id = 0;
+		goto out;
+	}
+	err = 0;
+out:
+	bpf_object__close(obj);
+	return err;
+}
+
+static int syncookie_open_bpf_maps(__u32 prog_id, int *values_map_fd, int *ports_map_fd)
+{
+	struct bpf_prog_info prog_info;
+	__u32 map_ids[8];
+	__u32 info_len;
+	int prog_fd;
+	int err;
+	int i;
+
+	*values_map_fd = -1;
+	*ports_map_fd = -1;
+
+	prog_fd = bpf_prog_get_fd_by_id(prog_id);
+	if (prog_fd < 0) {
+		fprintf(stderr, "Error: bpf_prog_get_fd_by_id: %s\n", strerror(-prog_fd));
+		return prog_fd;
+	}
+
+	prog_info = (struct bpf_prog_info) {
+		.nr_map_ids = 8,
+		.map_ids = (__u64)map_ids,
+	};
+	info_len = sizeof(prog_info);
+
+	err = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &info_len);
+	if (err != 0) {
+		fprintf(stderr, "Error: bpf_obj_get_info_by_fd: %s\n", strerror(-err));
+		goto out;
+	}
+
+	if (prog_info.type != BPF_PROG_TYPE_XDP) {
+		fprintf(stderr, "Error: BPF prog type is not BPF_PROG_TYPE_XDP\n");
+		err = -ENOENT;
+		goto out;
+	}
+	if (prog_info.nr_map_ids < 2) {
+		fprintf(stderr, "Error: Found %u BPF maps, expected at least 2\n",
+			prog_info.nr_map_ids);
+		err = -ENOENT;
+		goto out;
+	}
+
+	for (i = 0; i < prog_info.nr_map_ids; i++) {
+		struct bpf_map_info map_info = {};
+		int map_fd;
+
+		err = bpf_map_get_fd_by_id(map_ids[i]);
+		if (err < 0) {
+			fprintf(stderr, "Error: bpf_map_get_fd_by_id: %s\n", strerror(-err));
+			goto err_close_map_fds;
+		}
+		map_fd = err;
+
+		info_len = sizeof(map_info);
+		err = bpf_obj_get_info_by_fd(map_fd, &map_info, &info_len);
+		if (err != 0) {
+			fprintf(stderr, "Error: bpf_obj_get_info_by_fd: %s\n", strerror(-err));
+			close(map_fd);
+			goto err_close_map_fds;
+		}
+		if (strcmp(map_info.name, "values") == 0) {
+			*values_map_fd = map_fd;
+			continue;
+		}
+		if (strcmp(map_info.name, "allowed_ports") == 0) {
+			*ports_map_fd = map_fd;
+			continue;
+		}
+		close(map_fd);
+	}
+
+	if (*values_map_fd != -1 && *ports_map_fd != -1) {
+		err = 0;
+		goto out;
+	}
+
+	err = -ENOENT;
+
+err_close_map_fds:
+	if (*values_map_fd != -1)
+		close(*values_map_fd);
+	if (*ports_map_fd != -1)
+		close(*ports_map_fd);
+	*values_map_fd = -1;
+	*ports_map_fd = -1;
+
+out:
+	close(prog_fd);
+	return err;
+}
+
+int main(int argc, char *argv[])
+{
+	int values_map_fd, ports_map_fd;
+	__u64 tcpipopts;
+	bool firstiter;
+	__u64 prevcnt;
+	__u32 prog_id;
+	char *ports;
+	bool single;
+	int err = 0;
+
+	parse_options(argc, argv, &ifindex, &prog_id, &tcpipopts, &ports, &single);
+
+	if (prog_id == 0) {
+		err = bpf_xdp_query_id(ifindex, 0, &prog_id);
+		if (err < 0) {
+			fprintf(stderr, "Error: bpf_get_link_xdp_id: %s\n", strerror(-err));
+			goto out;
+		}
+		if (prog_id == 0) {
+			err = syncookie_attach(argv[0], ifindex);
+			if (err < 0)
+				goto out;
+			prog_id = attached_prog_id;
+		}
+	}
+
+	err = syncookie_open_bpf_maps(prog_id, &values_map_fd, &ports_map_fd);
+	if (err < 0)
+		goto out;
+
+	if (ports) {
+		__u16 port_last = 0;
+		__u32 port_idx = 0;
+		char *p = ports;
+
+		fprintf(stderr, "Replacing allowed ports\n");
+
+		while (p && *p != '\0') {
+			char *token = strsep(&p, ",");
+			__u16 port;
+
+			port = parse_arg_ul(argv[0], token, UINT16_MAX);
+			err = bpf_map_update_elem(ports_map_fd, &port_idx, &port, BPF_ANY);
+			if (err != 0) {
+				fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err));
+				fprintf(stderr, "Failed to add port %u (index %u)\n",
+					port, port_idx);
+				goto out_close_maps;
+			}
+			fprintf(stderr, "Added port %u\n", port);
+			port_idx++;
+		}
+		err = bpf_map_update_elem(ports_map_fd, &port_idx, &port_last, BPF_ANY);
+		if (err != 0) {
+			fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err));
+			fprintf(stderr, "Failed to add the terminator value 0 (index %u)\n",
+				port_idx);
+			goto out_close_maps;
+		}
+	}
+
+	if (tcpipopts) {
+		__u32 key = 0;
+
+		fprintf(stderr, "Replacing TCP/IP options\n");
+
+		err = bpf_map_update_elem(values_map_fd, &key, &tcpipopts, BPF_ANY);
+		if (err != 0) {
+			fprintf(stderr, "Error: bpf_map_update_elem: %s\n", strerror(-err));
+			goto out_close_maps;
+		}
+	}
+
+	if ((ports || tcpipopts) && attached_prog_id == 0 && !single)
+		goto out_close_maps;
+
+	prevcnt = 0;
+	firstiter = true;
+	while (true) {
+		__u32 key = 1;
+		__u64 value;
+
+		err = bpf_map_lookup_elem(values_map_fd, &key, &value);
+		if (err != 0) {
+			fprintf(stderr, "Error: bpf_map_lookup_elem: %s\n", strerror(-err));
+			goto out_close_maps;
+		}
+		if (firstiter) {
+			prevcnt = value;
+			firstiter = false;
+		}
+		if (single) {
+			printf("Total SYNACKs generated: %llu\n", value);
+			break;
+		}
+		printf("SYNACKs generated: %llu (total %llu)\n", value - prevcnt, value);
+		prevcnt = value;
+		sleep(1);
+	}
+
+out_close_maps:
+	close(values_map_fd);
+	close(ports_map_fd);
+out:
+	return err == 0 ? 0 : 1;
+}