[RFC,nf-next,1/3] bpf: add bpf_link support for BPF_NETFILTER programs

Commit Message

Florian Westphal Feb. 8, 2023, 4:03 p.m. UTC

Add bpf_link support skeleton.  To keep this reviewable, no bpf program
can be invoked here, if a program would be attached only a c-stub is called.

This defaults to 'y' if both netfilter and bpf syscall are enabled in
kconfig.

Uapi example usage:
	union bpf_attr attr = { };

	attr.link_create.prog_fd = progfd;
	attr.link_create.attach_type = BPF_NETFILTER;
	attr.link_create.netfilter.pf = PF_INET;
	attr.link_create.netfilter.hooknum = NF_INET_LOCAL_IN;
	attr.link_create.netfilter.priority = -128;

	err = bpf(BPF_LINK_CREATE, &attr, sizeof(attr));

... this would attach progfd to ipv4:input hook.

Such hook gets removed automatically if the calling program exits.

BPF_NETFILTER program invocation is added in followup change.

NF_HOOK_OP_BPF enum will eventually be read from nfnetlink_hook, it
allows to tell userspace which program is attached at the given hook
when user runs 'nft hook list' command rather than just the priority
and not-very-helpful 'this hook runs a bpf prog but I can't tell which
one'.

Signed-off-by: Florian Westphal <[e-mail]>
---
 include/linux/netfilter.h           |   1 +
 include/net/netfilter/nf_hook_bpf.h |   2 +
 include/uapi/linux/bpf.h            |  13 ++++
 kernel/bpf/syscall.c                |   7 ++
 net/netfilter/Kconfig               |   3 +
 net/netfilter/Makefile              |   1 +
 net/netfilter/nf_bpf_link.c         | 116 ++++++++++++++++++++++++++++
 7 files changed, 143 insertions(+)
 create mode 100644 include/net/netfilter/nf_hook_bpf.h
 create mode 100644 net/netfilter/nf_bpf_link.c

Patch

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index d8817d381c14..c5d51c389fd4 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -80,6 +80,7 @@  typedef unsigned int nf_hookfn(void *priv,
 enum nf_hook_ops_type {
 	NF_HOOK_OP_UNDEFINED,
 	NF_HOOK_OP_NF_TABLES,
+	NF_HOOK_OP_BPF,
 };
 
 struct nf_hook_ops {
diff --git a/include/net/netfilter/nf_hook_bpf.h b/include/net/netfilter/nf_hook_bpf.h
new file mode 100644
index 000000000000..9d1b338e89d7
--- /dev/null
+++ b/include/net/netfilter/nf_hook_bpf.h
@@ -0,0 +1,2 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ba0f0cfb5e42..ff2fccef91af 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -986,6 +986,7 @@  enum bpf_prog_type {
 	BPF_PROG_TYPE_LSM,
 	BPF_PROG_TYPE_SK_LOOKUP,
 	BPF_PROG_TYPE_SYSCALL, /* a program that can execute syscalls */
+	BPF_PROG_TYPE_NETFILTER,
 };
 
 enum bpf_attach_type {
@@ -1033,6 +1034,7 @@  enum bpf_attach_type {
 	BPF_PERF_EVENT,
 	BPF_TRACE_KPROBE_MULTI,
 	BPF_LSM_CGROUP,
+	BPF_NETFILTER,
 	__MAX_BPF_ATTACH_TYPE
 };
 
@@ -1049,6 +1051,7 @@  enum bpf_link_type {
 	BPF_LINK_TYPE_PERF_EVENT = 7,
 	BPF_LINK_TYPE_KPROBE_MULTI = 8,
 	BPF_LINK_TYPE_STRUCT_OPS = 9,
+	BPF_LINK_TYPE_NETFILTER = 10,
 
 	MAX_BPF_LINK_TYPE,
 };
@@ -1543,6 +1546,11 @@  union bpf_attr {
 				 */
 				__u64		cookie;
 			} tracing;
+			struct {
+				__u32		pf;
+				__u32		hooknum;
+				__s32		prio;
+			} netfilter;
 		};
 	} link_create;
 
@@ -6354,6 +6362,11 @@  struct bpf_link_info {
 		struct {
 			__u32 ifindex;
 		} xdp;
+		struct {
+			__u32 pf;
+			__u32 hooknum;
+			__s32 priority;
+		} netfilter;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 99417b387547..f3e7aae44c6a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -35,6 +35,7 @@ 
 #include <linux/rcupdate_trace.h>
 #include <linux/memcontrol.h>
 #include <linux/trace_events.h>
+#include <net/netfilter/nf_hook_bpf.h>
 
 #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
 			  (map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
@@ -2433,6 +2434,7 @@  static bool is_net_admin_prog_type(enum bpf_prog_type prog_type)
 	case BPF_PROG_TYPE_CGROUP_SYSCTL:
 	case BPF_PROG_TYPE_SOCK_OPS:
 	case BPF_PROG_TYPE_EXT: /* extends any prog */
+	case BPF_PROG_TYPE_NETFILTER:
 		return true;
 	case BPF_PROG_TYPE_CGROUP_SKB:
 		/* always unpriv */
@@ -3460,6 +3462,8 @@  attach_type_to_prog_type(enum bpf_attach_type attach_type)
 		return BPF_PROG_TYPE_XDP;
 	case BPF_LSM_CGROUP:
 		return BPF_PROG_TYPE_LSM;
+	case BPF_NETFILTER:
+		return BPF_PROG_TYPE_NETFILTER;
 	default:
 		return BPF_PROG_TYPE_UNSPEC;
 	}
@@ -4613,6 +4617,9 @@  static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	case BPF_PROG_TYPE_XDP:
 		ret = bpf_xdp_link_attach(attr, prog);
 		break;
+	case BPF_PROG_TYPE_NETFILTER:
+		ret = bpf_nf_link_attach(attr, prog);
+		break;
 #endif
 	case BPF_PROG_TYPE_PERF_EVENT:
 	case BPF_PROG_TYPE_TRACEPOINT:
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index f71b41c7ce2f..237f3d411164 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -30,6 +30,9 @@  config NETFILTER_FAMILY_BRIDGE
 config NETFILTER_FAMILY_ARP
 	bool
 
+config NETFILTER_BPF_LINK
+	def_bool BPF_SYSCALL
+
 config NETFILTER_NETLINK_HOOK
 	tristate "Netfilter base hook dump support"
 	depends on NETFILTER_ADVANCED
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index ba2a6b5e93d9..ca12f559a04d 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -21,6 +21,7 @@  nf_conntrack-$(CONFIG_DEBUG_INFO_BTF) += nf_conntrack_bpf.o
 endif
 
 obj-$(CONFIG_NETFILTER) = netfilter.o
+obj-$(CONFIG_NETFILTER_BPF_LINK) += nf_bpf_link.o
 
 obj-$(CONFIG_NETFILTER_NETLINK) += nfnetlink.o
 obj-$(CONFIG_NETFILTER_NETLINK_ACCT) += nfnetlink_acct.o
diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
new file mode 100644
index 000000000000..fa4fae5cc669
--- /dev/null
+++ b/net/netfilter/nf_bpf_link.c
@@ -0,0 +1,116 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <linux/netfilter.h>
+
+#include <net/netfilter/nf_hook_bpf.h>
+
+static unsigned int nf_hook_run_bpf(void *bpf_prog, struct sk_buff *skb, const struct nf_hook_state *s)
+{
+	return NF_ACCEPT;
+}
+
+struct bpf_nf_link {
+	struct bpf_link link;
+	struct nf_hook_ops hook_ops;
+	struct net *net;
+};
+
+static void bpf_nf_link_release(struct bpf_link *link)
+{
+	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+
+	nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
+}
+
+static void bpf_nf_link_dealloc(struct bpf_link *link)
+{
+	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+
+	kfree(nf_link);
+}
+
+static int bpf_nf_link_detach(struct bpf_link *link)
+{
+	bpf_nf_link_release(link);
+	return 0;
+}
+
+static void bpf_nf_link_show_info(const struct bpf_link *link,
+				  struct seq_file *seq)
+{
+	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+
+	seq_printf(seq, "pf:\t%u\thooknum:\t%u\tprio:\t%d\n",
+		  nf_link->hook_ops.pf, nf_link->hook_ops.hooknum,
+		  nf_link->hook_ops.priority);
+}
+
+static int bpf_nf_link_fill_link_info(const struct bpf_link *link,
+				      struct bpf_link_info *info)
+{
+	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);
+
+	info->netfilter.pf = nf_link->hook_ops.pf;
+	info->netfilter.hooknum = nf_link->hook_ops.hooknum;
+	info->netfilter.priority = nf_link->hook_ops.priority;
+
+	return 0;
+}
+
+static int bpf_nf_link_update(struct bpf_link *link, struct bpf_prog *new_prog,
+			      struct bpf_prog *old_prog)
+{
+	return -EOPNOTSUPP;
+}
+
+static const struct bpf_link_ops bpf_nf_link_lops = {
+	.release = bpf_nf_link_release,
+	.dealloc = bpf_nf_link_dealloc,
+	.detach = bpf_nf_link_detach,
+	.show_fdinfo = bpf_nf_link_show_info,
+	.fill_link_info = bpf_nf_link_fill_link_info,
+	.update_prog = bpf_nf_link_update,
+};
+
+int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
+{
+	struct net *net = current->nsproxy->net_ns;
+	struct bpf_link_primer link_primer;
+	struct bpf_nf_link *link;
+	int err;
+
+	if (attr->link_create.flags)
+		return -EINVAL;
+
+	link = kzalloc(sizeof(*link), GFP_USER);
+	if (!link)
+		return -ENOMEM;
+
+	bpf_link_init(&link->link, BPF_LINK_TYPE_NETFILTER, &bpf_nf_link_lops, prog);
+
+	link->hook_ops.hook = nf_hook_run_bpf;
+	link->hook_ops.hook_ops_type = NF_HOOK_OP_BPF;
+	link->hook_ops.priv = prog;
+
+	link->hook_ops.pf = attr->link_create.netfilter.pf;
+	link->hook_ops.priority = attr->link_create.netfilter.prio;
+	link->hook_ops.hooknum = attr->link_create.netfilter.hooknum;
+
+	link->net = net;
+
+	err = bpf_link_prime(&link->link, &link_primer);
+	if (err)
+		goto out_free;
+
+	err = nf_register_net_hook(net, &link->hook_ops);
+	if (err) {
+		bpf_link_cleanup(&link_primer);
+		goto out_free;
+	}
+
+	return bpf_link_settle(&link_primer);
+
+out_free:
+	kfree(link);
+	return err;
+}