From: Xin Long <lucien.xin@gmail.com>
Date: Wed, 20 Oct 2021 07:42:44 -0400
Subject: sctp: fix the processing for COOKIE_ECHO chunk
Patch-mainline: v5.15
Git-commit: a64b341b8695e1c744dd972b39868371b4f68f83
References: CVE-2021-3772 bsc#1190351

1. In closed state: in sctp_sf_do_5_1D_ce():

  When asoc is NULL, making packet for abort will use chunk's vtag
  in sctp_ootb_pkt_new(). But when asoc exists, vtag from the chunk
  should be verified before using peer.i.init_tag to make packet
  for abort in sctp_ootb_pkt_new(), and just discard it if vtag is
  not correct.

2. In the other states: in sctp_sf_do_5_2_4_dupcook():

  asoc always exists, but duplicate cookie_echo's vtag will be
  handled by sctp_tietags_compare() and then take actions, so before
  that we only verify the vtag for the abort sent for invalid chunk
  length.

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 | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -695,6 +695,9 @@ sctp_disposition_t sctp_sf_do_5_1D_ce(struct net *net,
 	struct sctp_chunk *err_chk_p;
 	struct sock *sk;
 
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+
 	/* If the packet is an OOTB packet which is temporarily on the
 	 * control endpoint, respond with an ABORT.
 	 */
@@ -709,7 +712,8 @@ sctp_disposition_t sctp_sf_do_5_1D_ce(struct net *net,
 	 * in sctp_unpack_cookie().
 	 */
 	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_chunkhdr_t)))
-		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
+						  commands);
 
 	/* If the endpoint is not listening or if the number of associations
 	 * on the TCP-style socket exceed the max backlog, respond with an
@@ -2057,9 +2061,11 @@ sctp_disposition_t sctp_sf_do_5_2_4_dupcook(struct net *net,
 	 * enough for the chunk header.  Cookie length verification is
 	 * done later.
 	 */
-	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_chunkhdr_t)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
+	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_chunkhdr_t))) {
+		if (!sctp_vtag_verify(chunk, asoc))
+			asoc = NULL;
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg, commands);
+	}
 
 	/* "Decode" the chunk.  We have no optional parameters so we
 	 * are in good shape.