[PATCH bpf-next] bpf: Allow bpf_tcp_sock() helper in XDP

[Arthur Fabre]

We can already lookup sockets in XDP via the bpf_sk(c)_lookup_(udp|tcp)
helpers. This can be used to determine if a received packet is for an
established socket or not, for example in a load balancer.

But the TCP TIME-WAIT state needs special handling for this: packets
received for a TIME-WAIT socket can either belong to the current
incarnation of the connection, or a new incarnation. The only way to
determine this is to compare the sequence numbers.

Add the bpf_tcp_sock() helper in XDP to allow the socket sequence
numbers to be read.

---
Signed-off-by: Arthur Fabre <afabre@xxxxxxxxxxxxxx>
---
 net/core/filter.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index f04982d79d72e92f1b46ccd87633391e38c3da81..5e3a1951130369f070c3a373ea649bd10db412b6 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8506,6 +8506,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_sk_release_proto;
 	case BPF_FUNC_skc_lookup_tcp:
 		return &bpf_xdp_skc_lookup_tcp_proto;
+	case BPF_FUNC_tcp_sock:
+		return &bpf_tcp_sock_proto;
 	case BPF_FUNC_tcp_check_syncookie:
 		return &bpf_tcp_check_syncookie_proto;
 	case BPF_FUNC_tcp_gen_syncookie:

---
base-commit: d95d76aa772bf94df353b015b1cb38303d4a415d
change-id: 20260204-afabre-bpf_tcp_sock-117d03c6f0e3

Best regards,
-- 
Arthur Fabre <afabre@xxxxxxxxxxxxxx>