sctp: fix missing encap_port propagation for GSO fragments

[ Upstream commit bf6f95a ]

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: 046c052 ("sctp: enable udp tunneling socks")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Link: https://patch.msgid.link/ea65ed61b3598d8b4940f0170b9aa1762307e6c3.1776017631.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: lxin

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;
 		}
 	}