sctp: Catch bogus stream sequence numbers

Since our TSN map is capable of holding at most a 4K chunk gap,
there is no way that during this gap, a stream sequence number
(unsigned short) can wrap such that the new number is smaller
then the next expected one.  If such a case is encountered,
this is a protocol violation.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>

1 files changed, 26 insertions, 2 deletions

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index a7f18a352364..c8fae1983dd1 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -2891,6 +2891,9 @@ sctp_disposition_t sctp_sf_eat_data_6_2(const struct sctp_endpoint *ep,
                 goto discard_force;
         case SCTP_IERROR_NO_DATA:
                 goto consume;
+        case SCTP_IERROR_PROTO_VIOLATION:
+                return sctp_sf_abort_violation(ep, asoc, chunk, commands,
+                        (u8 *)chunk->subh.data_hdr, sizeof(sctp_datahdr_t));
         default:
                 BUG();
         }
@@ -3001,6 +3004,9 @@ sctp_disposition_t sctp_sf_eat_data_fast_4_4(const struct sctp_endpoint *ep,
                 break;
         case SCTP_IERROR_NO_DATA:
                 goto consume;
+        case SCTP_IERROR_PROTO_VIOLATION:
+                return sctp_sf_abort_violation(ep, asoc, chunk, commands,
+                        (u8 *)chunk->subh.data_hdr, sizeof(sctp_datahdr_t));
         default:
                 BUG();
         }
@@ -5877,6 +5883,9 @@ static int sctp_eat_data(const struct sctp_association *asoc,
         __u32 tsn;
         struct sctp_tsnmap *map = (struct sctp_tsnmap *)&asoc->peer.tsn_map;
         struct sock *sk = asoc->base.sk;
+        u16 ssn;
+        u16 sid;
+        u8 ordered = 0;
 
         data_hdr = chunk->subh.data_hdr = (sctp_datahdr_t *)chunk->skb->data;
         skb_pull(chunk->skb, sizeof(sctp_datahdr_t));
@@ -6016,8 +6025,10 @@ static int sctp_eat_data(const struct sctp_association *asoc,
          */
         if (chunk->chunk_hdr->flags & SCTP_DATA_UNORDERED)
                 SCTP_INC_STATS(SCTP_MIB_INUNORDERCHUNKS);
-        else
+        else {
                 SCTP_INC_STATS(SCTP_MIB_INORDERCHUNKS);
+                ordered = 1;
+        }
 
         /* RFC 2960 6.5 Stream Identifier and Stream Sequence Number
          *
@@ -6027,7 +6038,8 @@ static int sctp_eat_data(const struct sctp_association *asoc,
          * with cause set to "Invalid Stream Identifier" (See Section 3.3.10)
          * and discard the DATA chunk.
          */
-        if (ntohs(data_hdr->stream) >= asoc->c.sinit_max_instreams) {
+        sid = ntohs(data_hdr->stream);
+        if (sid >= asoc->c.sinit_max_instreams) {
                 /* Mark tsn as received even though we drop it */
                 sctp_add_cmd_sf(commands, SCTP_CMD_REPORT_TSN, SCTP_U32(tsn));
 
@@ -6040,6 +6052,18 @@ static int sctp_eat_data(const struct sctp_association *asoc,
                 return SCTP_IERROR_BAD_STREAM;
         }
 
+        /* Check to see if the SSN is possible for this TSN.
+         * The biggest gap we can record is 4K wide.  Since SSNs wrap
+         * at an unsigned short, there is no way that an SSN can
+         * wrap and for a valid TSN.  We can simply check if the current
+         * SSN is smaller then the next expected one.  If it is, it wrapped
+         * and is invalid.
+         */
+        ssn = ntohs(data_hdr->ssn);
+        if (ordered && SSN_lt(ssn, sctp_ssn_peek(&asoc->ssnmap->in, sid))) {
+                return SCTP_IERROR_PROTO_VIOLATION;
+        }
+
         /* Send the data up to the user.  Note:  Schedule  the
          * SCTP_CMD_CHUNK_ULP cmd before the SCTP_CMD_GEN_SACK, as the SACK
          * chunk needs the updated rwnd.