[bpf-next,v3,1/2] bpf: Add ipip6 and ip6ip decap support for bpf_skb_adjust_room()

Commit Message

Ziyang Xuan (William) Jan. 13, 2023, 9:24 a.m. UTC

Add ipip6 and ip6ip decap support for bpf_skb_adjust_room().
Main use case is for using cls_bpf on ingress hook to decapsulate
IPv4 over IPv6 and IPv6 over IPv4 tunnel packets.

Add two new flags BPF_F_ADJ_ROOM_DECAP_L3_IPV{4,6} to indicate the
new IP header version after decapsulating the outer IP header.

Suggested-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Ziyang Xuan <[e-mail]>
---
 include/uapi/linux/bpf.h       |  7 +++++++
 net/core/filter.c              | 31 ++++++++++++++++++++++++++++++-
 tools/include/uapi/linux/bpf.h |  7 +++++++
 3 files changed, 44 insertions(+), 1 deletion(-)

Comments

Willem de Bruijn Jan. 13, 2023, 2:10 p.m. UTC | #1

On Fri, Jan 13, 2023 at 4:25 AM Ziyang Xuan
<[e-mail]> wrote:
>
> Add ipip6 and ip6ip decap support for bpf_skb_adjust_room().
> Main use case is for using cls_bpf on ingress hook to decapsulate
> IPv4 over IPv6 and IPv6 over IPv4 tunnel packets.
>
> Add two new flags BPF_F_ADJ_ROOM_DECAP_L3_IPV{4,6} to indicate the
> new IP header version after decapsulating the outer IP header.
>
> Suggested-by: Willem de Bruijn <[e-mail]>
> Signed-off-by: Ziyang Xuan <[e-mail]>

Reviewed-by: Willem de Bruijn <[e-mail]>

Patch

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 464ca3f01fe7..b6c1720a7abf 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2644,6 +2644,11 @@  union bpf_attr {
  *		  Use with BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the
  *		  L2 type as Ethernet.
  *
+ *		* **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**,
+ *		  **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**:
+ *		  Indicate the new IP header version after decapsulating the outer
+ *		  IP header. Used when the inner and outer IP versions are different.
+ *
  * 		A call to this helper is susceptible to change the underlying
  * 		packet buffer. Therefore, at load time, all checks on pointers
  * 		previously done by the verifier are invalidated and must be
@@ -5803,6 +5808,8 @@  enum {
 	BPF_F_ADJ_ROOM_ENCAP_L4_UDP	= (1ULL << 4),
 	BPF_F_ADJ_ROOM_NO_CSUM_RESET	= (1ULL << 5),
 	BPF_F_ADJ_ROOM_ENCAP_L2_ETH	= (1ULL << 6),
+	BPF_F_ADJ_ROOM_DECAP_L3_IPV4	= (1ULL << 7),
+	BPF_F_ADJ_ROOM_DECAP_L3_IPV6	= (1ULL << 8),
 };
 
 enum {
diff --git a/net/core/filter.c b/net/core/filter.c
index 43cc1fe58a2c..4c9c4e6b1f6c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3381,13 +3381,17 @@  static u32 bpf_skb_net_base_len(const struct sk_buff *skb)
 #define BPF_F_ADJ_ROOM_ENCAP_L3_MASK	(BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 | \
 					 BPF_F_ADJ_ROOM_ENCAP_L3_IPV6)
 
+#define BPF_F_ADJ_ROOM_DECAP_L3_MASK	(BPF_F_ADJ_ROOM_DECAP_L3_IPV4 | \
+					 BPF_F_ADJ_ROOM_DECAP_L3_IPV6)
+
 #define BPF_F_ADJ_ROOM_MASK		(BPF_F_ADJ_ROOM_FIXED_GSO | \
 					 BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \
 					 BPF_F_ADJ_ROOM_ENCAP_L4_GRE | \
 					 BPF_F_ADJ_ROOM_ENCAP_L4_UDP | \
 					 BPF_F_ADJ_ROOM_ENCAP_L2_ETH | \
 					 BPF_F_ADJ_ROOM_ENCAP_L2( \
-					  BPF_ADJ_ROOM_ENCAP_L2_MASK))
+					  BPF_ADJ_ROOM_ENCAP_L2_MASK) | \
+					 BPF_F_ADJ_ROOM_DECAP_L3_MASK)
 
 static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
 			    u64 flags)
@@ -3501,6 +3505,7 @@  static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
 	int ret;
 
 	if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO |
+			       BPF_F_ADJ_ROOM_DECAP_L3_MASK |
 			       BPF_F_ADJ_ROOM_NO_CSUM_RESET)))
 		return -EINVAL;
 
@@ -3519,6 +3524,14 @@  static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
 	if (unlikely(ret < 0))
 		return ret;
 
+	/* Match skb->protocol to new outer l3 protocol */
+	if (skb->protocol == htons(ETH_P_IP) &&
+	    flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV6)
+		skb->protocol = htons(ETH_P_IPV6);
+	else if (skb->protocol == htons(ETH_P_IPV6) &&
+		 flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV4)
+		skb->protocol = htons(ETH_P_IP);
+
 	if (skb_is_gso(skb)) {
 		struct skb_shared_info *shinfo = skb_shinfo(skb);
 
@@ -3608,6 +3621,22 @@  BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
 		return -ENOTSUPP;
 	}
 
+	if (flags & BPF_F_ADJ_ROOM_DECAP_L3_MASK) {
+		if (!shrink)
+			return -EINVAL;
+
+		switch (flags & BPF_F_ADJ_ROOM_DECAP_L3_MASK) {
+		case BPF_F_ADJ_ROOM_DECAP_L3_IPV4:
+			len_min = sizeof(struct iphdr);
+			break;
+		case BPF_F_ADJ_ROOM_DECAP_L3_IPV6:
+			len_min = sizeof(struct ipv6hdr);
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
 	len_cur = skb->len - skb_network_offset(skb);
 	if ((shrink && (len_diff_abs >= len_cur ||
 			len_cur - len_diff_abs < len_min)) ||
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 464ca3f01fe7..fa9dc6b50fa8 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2644,6 +2644,11 @@  union bpf_attr {
  *		  Use with BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the
  *		  L2 type as Ethernet.
  *
+ *		* **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**,
+ *		  **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**:
+ *		  Indicate the new IP header version after decapsulating the outer
+ *		  IP header. Used when the inner and outer IP versions are different.
+ *
  * 		A call to this helper is susceptible to change the underlying
  * 		packet buffer. Therefore, at load time, all checks on pointers
  * 		previously done by the verifier are invalidated and must be
@@ -5803,6 +5808,8 @@  enum {
 	BPF_F_ADJ_ROOM_ENCAP_L4_UDP	= (1ULL << 4),
 	BPF_F_ADJ_ROOM_NO_CSUM_RESET	= (1ULL << 5),
 	BPF_F_ADJ_ROOM_ENCAP_L2_ETH	= (1ULL << 6),
+	BPF_F_ADJ_ROOM_DECAP_L3_IPV4    = (1ULL << 7),
+	BPF_F_ADJ_ROOM_DECAP_L3_IPV6    = (1ULL << 8),
 };
 
 enum {