From: Xin Long <lucien.xin@gmail.com>
Date: Wed, 20 Oct 2021 07:42:43 -0400
Subject: sctp: fix the processing for INIT_ACK chunk
Patch-mainline: v5.15
Git-commit: 438b95a7c98f77d51cbf4db021f41b602d750a3f
References: CVE-2021-3772 bsc#1190351

Currently INIT_ACK chunk in non-cookie_echoed state is processed in
sctp_sf_discard_chunk() to send an abort with the existent asoc's
vtag if the chunk length is not valid. But the vtag in the chunk's
sctphdr is not verified, which may be exploited by one to cook a
malicious chunk to terminal a SCTP asoc.

sctp_sf_discard_chunk() also is called in many other places to send
an abort, and most of those have this problem. This patch is to fix
it by sending abort with the existent asoc's vtag only if the vtag
from the chunk's sctphdr is verified in sctp_sf_discard_chunk().

Note on sctp_sf_do_9_1_abort() and sctp_sf_shutdown_pending_abort(),
the chunk length has been verified before sctp_sf_discard_chunk(),
so replace it with sctp_sf_discard(). On sctp_sf_do_asconf_ack() and
sctp_sf_do_asconf(), move the sctp_chunk_length_valid check ahead of
sctp_sf_discard_chunk(), then replace it with sctp_sf_discard().

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 | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -2200,7 +2200,7 @@ sctp_disposition_t sctp_sf_shutdown_pend
 	 */
 	if (SCTP_ADDR_DEL ==
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	if (!sctp_err_chunk_valid(chunk))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -2245,7 +2245,7 @@ sctp_disposition_t sctp_sf_shutdown_sent
 	 */
 	if (SCTP_ADDR_DEL ==
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	if (!sctp_err_chunk_valid(chunk))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -2513,7 +2513,7 @@ sctp_disposition_t sctp_sf_do_9_1_abort(
 	 */
 	if (SCTP_ADDR_DEL ==
 		    sctp_bind_addr_state(&asoc->base.bind_addr, &chunk->dest))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	if (!sctp_err_chunk_valid(chunk))
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
@@ -3656,6 +3656,11 @@ sctp_disposition_t sctp_sf_do_asconf(struct net *net,
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 	}
 
+	/* Make sure that the ASCONF ADDIP chunk has a valid length.  */
+	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_addip_chunk_t)))
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
+						  commands);
+
 	/* ADD-IP: Section 4.1.1
 	 * This chunk MUST be sent in an authenticated way by using
 	 * the mechanism defined in [I-D.ietf-tsvwg-sctp-auth]. If this chunk
@@ -3664,12 +3669,7 @@ sctp_disposition_t sctp_sf_do_asconf(struct net *net,
 	 */
 	if (!asoc->peer.asconf_capable ||
 	    (!net->sctp.addip_noauth && !chunk->auth))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
-
-	/* Make sure that the ASCONF ADDIP chunk has a valid length.  */
-	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_addip_chunk_t)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	hdr = (sctp_addiphdr_t *)chunk->skb->data;
 	serial = ntohl(hdr->serial);
@@ -3797,6 +3797,11 @@ sctp_disposition_t sctp_sf_do_asconf_ack(struct net *net,
 		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 	}
 
+	/* Make sure that the ADDIP chunk has a valid length.  */
+	if (!sctp_chunk_length_valid(asconf_ack, sizeof(sctp_addip_chunk_t)))
+		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
+						  commands);
+
 	/* ADD-IP, Section 4.1.2:
 	 * This chunk MUST be sent in an authenticated way by using
 	 * the mechanism defined in [I-D.ietf-tsvwg-sctp-auth]. If this chunk
@@ -3805,12 +3810,7 @@ sctp_disposition_t sctp_sf_do_asconf_ack(struct net *net,
 	 */
 	if (!asoc->peer.asconf_capable ||
 	    (!net->sctp.addip_noauth && !asconf_ack->auth))
-		return sctp_sf_discard_chunk(net, ep, asoc, type, arg, commands);
-
-	/* Make sure that the ADDIP chunk has a valid length.  */
-	if (!sctp_chunk_length_valid(asconf_ack, sizeof(sctp_addip_chunk_t)))
-		return sctp_sf_violation_chunklen(net, ep, asoc, type, arg,
-						  commands);
+		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
 
 	addip_hdr = (sctp_addiphdr_t *)asconf_ack->skb->data;
 	rcvd_serial = ntohl(addip_hdr->serial);
@@ -4387,6 +4387,9 @@ sctp_disposition_t sctp_sf_discard_chunk(struct net *net,
 {
 	struct sctp_chunk *chunk = arg;
 
+	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.
 	 * Since we don't know the chunk type, we use a general
 	 * chunkhdr structure to make a comparison.