Some callers (e.g. sctp_sf_violation_chunk) passes NULL to
asoc argument of sctp_sf_violation. So, it should check it
before calling sctp_vtag_verify().

Probably it could be exploited by a malicious SCTP packet
to cause NULL pointer dereference.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Alexey Khoroshilov <redacted>
Fixes: aa0f697e4528 ("sctp: add vtag check in sctp_sf_violation")
---
 net/sctp/sm_statefuns.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index fb3da4d8f4a3..77f3cd6c516e 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c

@@ -4669,7 +4669,7 @@ enum sctp_disposition sctp_sf_violation(struct net *net,
 {
 	struct sctp_chunk *chunk = arg;
 
-	if (!sctp_vtag_verify(chunk, asoc))
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	/* Make sure that the chunk has a valid length. */

-- 
2.7.4