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: 9fb9cbb1082d ("[NETFILTER]: Add nf_conntrack subsystem.")
Signed-off-by: Sriram Yagnaraman <sriram.yagnaraman@est.tech>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_conntrack_proto_sctp.c b/net/netfilter/nf_conntrack_proto_sctp.c
index d88b92a..2b2c549 100644 (file)
--- a/net/netfilter/nf_conntrack_proto_sctp.c
+++ b/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) {