From: Xin Long <lucien.xin@gmail.com>
Date: Wed, 20 Oct 2021 07:42:47 -0400
Subject: sctp: add vtag check in sctp_sf_ootb
Patch-mainline: v5.15
Git-commit: 9d02831e517aa36ee6bdb453a0eb47bd49923fe3
References: CVE-2021-3772 bsc#1190351

sctp_sf_ootb() is called when processing DATA chunk in closed state,
and many other places are also using it.

The vtag in the chunk's sctphdr should be verified, otherwise, as
later in chunk length check, it may send abort with the existent
asoc's vtag, which can be exploited by one to cook a malicious
chunk to terminate a SCTP asoc.

When fails to verify the vtag from the chunk, this patch sets asoc
to NULL, so that the abort will be made with the vtag from the
received chunk later.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/sctp/sm_statefuns.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -3481,6 +3481,9 @@ sctp_disposition_t sctp_sf_ootb(struct net *net,
 
 	SCTP_INC_STATS(net, SCTP_MIB_OUTOFBLUES);
 
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
+		asoc = NULL;
+
 	ch = (sctp_chunkhdr_t *) chunk->chunk_hdr;
 	do {
 		/* Report violation if the chunk is less then minimal */