[PATCH net] sctp: fix missing encap_port propagation for GSO fragments

[PATCH net] sctp: fix missing encap_port propagation for GSO fragments

[Xin Long]

encap_port in SCTP_INPUT_CB(skb) is used by sctp_vtag_verify() for
SCTP-over-UDP processing. In the GSO case, it is only set on the head
skb, while fragment skbs leave it 0.

This results in fragment skbs seeing encap_port == 0, breaking
SCTP-over-UDP connections.

Fix it by propagating encap_port from the head skb cb when initializing
fragment skbs in sctp_inq_pop().

Fixes: 046c052b475e ("sctp: enable udp tunneling socks")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/inqueue.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
index f5a7d5a38755..a024c0843247 100644
--- a/net/sctp/inqueue.c
+++ b/net/sctp/inqueue.c
@@ -201,6 +201,7 @@ struct sctp_chunk *sctp_inq_pop(struct sctp_inq *queue)
 
 			cb->chunk = head_cb->chunk;
 			cb->af = head_cb->af;
+			cb->encap_port = head_cb->encap_port;
 		}
 	}
 
-- 
2.47.1

Re: [PATCH net] sctp: fix missing encap_port propagation for GSO fragments

[Marcelo Ricardo Leitner]

On Sun, Apr 12, 2026 at 02:13:51PM -0400, Xin Long wrote:
> encap_port in SCTP_INPUT_CB(skb) is used by sctp_vtag_verify() for
> SCTP-over-UDP processing. In the GSO case, it is only set on the head
> skb, while fragment skbs leave it 0.
> 
> This results in fragment skbs seeing encap_port == 0, breaking
> SCTP-over-UDP connections.
> 
> Fix it by propagating encap_port from the head skb cb when initializing
> fragment skbs in sctp_inq_pop().
> 
> Fixes: 046c052b475e ("sctp: enable udp tunneling socks")
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Re: [PATCH net] sctp: fix missing encap_port propagation for GSO fragments

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Sun, 12 Apr 2026 14:13:51 -0400 you wrote:
> encap_port in SCTP_INPUT_CB(skb) is used by sctp_vtag_verify() for
> SCTP-over-UDP processing. In the GSO case, it is only set on the head
> skb, while fragment skbs leave it 0.
> 
> This results in fragment skbs seeing encap_port == 0, breaking
> SCTP-over-UDP connections.
> 
> [...]

Here is the summary with links:
  - [net] sctp: fix missing encap_port propagation for GSO fragments
    https://git.kernel.org/netdev/net/c/bf6f95ae3b8b

You are awesome, thank you!
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