[PATCH net] sctp: use the correct skb for security_sctp_assoc_request

[Xin Long <lucien.xin@gmail.com>]

Yi Chen reported an unexpected sctp connection abort, and it occurred when
COOKIE_ECHO is bundled with DATA Fragment by SCTP HW GSO. As the IP header
is included in chunk->head_skb instead of chunk->skb, it failed to check
IP header version in security_sctp_assoc_request().

According to Ondrej, SELinux only looks at IP header (address and IPsec
options) and XFRM state data, and these are all included in head_skb for
SCTP HW GSO packets. So fix it by using head_skb when calling
security_sctp_assoc_request() in processing COOKIE_ECHO.

Fixes: e215dab1c490 ("security: call security_sctp_assoc_request in sctp_sf_do_5_1D_ce")
Reported-by: Yi Chen <yiche@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/sm_statefuns.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 7f342bc12735..883f9b849ee5 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -781,7 +781,7 @@ enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net,
 		}
 	}
 
-	if (security_sctp_assoc_request(new_asoc, chunk->skb)) {
+	if (security_sctp_assoc_request(new_asoc, chunk->head_skb ?: chunk->skb)) {
 		sctp_association_free(new_asoc);
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 	}
@@ -2262,7 +2262,7 @@ enum sctp_disposition sctp_sf_do_5_2_4_dupcook(
 	}
 
 	/* Update socket peer label if first association. */
-	if (security_sctp_assoc_request(new_asoc, chunk->skb)) {
+	if (security_sctp_assoc_request(new_asoc, chunk->head_skb ?: chunk->skb)) {
 		sctp_association_free(new_asoc);
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 	}
-- 
2.31.1