netfilter: conntrack: fix vtag checks for ABORT/SHUTDOWN_COMPLETE

RFC 9260, Sec 8.5.1 states that for ABORT/SHUTDOWN_COMPLETE, the chunk
MUST be accepted if the vtag of the packet matches its own tag and the
T bit is not set OR if it is set to its peer's vtag and the T bit is set
in chunk flags. Otherwise the packet MUST be silently dropped.

Update vtag verification for ABORT/SHUTDOWN_COMPLETE based on the above
description.

Fixes: 9fb9cbb1 ("[NETFILTER]: Add nf_conntrack subsystem.")
Signed-off-by: Sriram Yagnaraman <sriram.yagnaraman@est.tech>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_proto_sctp.c

@@ -424,22 +424,29 @@ int nf_conntrack_sctp_packet(struct nf_conn *ct,
 	for_each_sctp_chunk (skb, sch, _sch, offset, dataoff, count) {
 		/* Special cases of Verification tag check (Sec 8.5.1) */
 		if (sch->type == SCTP_CID_INIT) {
-			/* Sec 8.5.1 (A) */
+			/* (A) vtag MUST be zero */
 			if (sh->vtag != 0)
 				goto out_unlock;
 		} else if (sch->type == SCTP_CID_ABORT) {
-			/* Sec 8.5.1 (B) */
-			if (sh->vtag != ct->proto.sctp.vtag[dir] &&
-			    sh->vtag != ct->proto.sctp.vtag[!dir])
+			/* (B) vtag MUST match own vtag if T flag is unset OR
+			 * MUST match peer's vtag if T flag is set
+			 */
+			if ((!(sch->flags & SCTP_CHUNK_FLAG_T) &&
+			     sh->vtag != ct->proto.sctp.vtag[dir]) ||
+			    ((sch->flags & SCTP_CHUNK_FLAG_T) &&
+			     sh->vtag != ct->proto.sctp.vtag[!dir]))
 				goto out_unlock;
 		} else if (sch->type == SCTP_CID_SHUTDOWN_COMPLETE) {
-			/* Sec 8.5.1 (C) */
-			if (sh->vtag != ct->proto.sctp.vtag[dir] &&
-			    sh->vtag != ct->proto.sctp.vtag[!dir] &&
-			    sch->flags & SCTP_CHUNK_FLAG_T)
+			/* (C) vtag MUST match own vtag if T flag is unset OR
+			 * MUST match peer's vtag if T flag is set
+			 */
+			if ((!(sch->flags & SCTP_CHUNK_FLAG_T) &&
+			     sh->vtag != ct->proto.sctp.vtag[dir]) ||
+			    ((sch->flags & SCTP_CHUNK_FLAG_T) &&
+			     sh->vtag != ct->proto.sctp.vtag[!dir]))
 				goto out_unlock;
 		} else if (sch->type == SCTP_CID_COOKIE_ECHO) {
-			/* Sec 8.5.1 (D) */
+			/* (D) vtag must be same as init_vtag as found in INIT_ACK */
 			if (sh->vtag != ct->proto.sctp.vtag[dir])
 				goto out_unlock;
 		} else if (sch->type == SCTP_CID_HEARTBEAT) {