SCTP: drop SACK if ctsn is not less than the next tsn of assoc

We need to drop the SACK if the peer is attempting to acknowledge
unset data, i.e.  the CTSN in the SACK is greater or equal to the
next TSN we will send.

Example:
Endpoint A                                      Endpoint B
                             <---------------   DATA (TSN=1)
SACK(TSN=1) ---------------> 
                             <---------------   DATA (TSN=2)
                             <---------------   DATA (TSN=3)
                             <---------------   DATA (TSN=4)
                             <---------------   DATA (TSN=5)
SACK(TSN=1000) --------------->
                             <---------------   DATA (TSN=6)
                             <---------------   DATA (TSN=7)

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>

net/sctp/sm_statefuns.c

@@ -97,6 +97,13 @@ static sctp_disposition_t sctp_stop_t1_and_abort(sctp_cmd_seq_t *commands,
 					   const struct sctp_association *asoc,
 					   struct sctp_transport *transport);
 
+static sctp_disposition_t sctp_sf_abort_violation(
+				     const struct sctp_association *asoc,
+				     void *arg,
+				     sctp_cmd_seq_t *commands,
+				     const __u8 *payload,
+				     const size_t paylen);
+
 static sctp_disposition_t sctp_sf_violation_chunklen(
 				     const struct sctp_endpoint *ep,
 				     const struct sctp_association *asoc,
@@ -104,6 +111,13 @@ static sctp_disposition_t sctp_sf_violation_chunklen(
 				     void *arg,
 				     sctp_cmd_seq_t *commands);
 
+static sctp_disposition_t sctp_sf_violation_ctsn(
+				     const struct sctp_endpoint *ep,
+				     const struct sctp_association *asoc,
+				     const sctp_subtype_t type,
+				     void *arg,
+				     sctp_cmd_seq_t *commands);
+
 /* Small helper function that checks if the chunk length
  * is of the appropriate length.  The 'required_length' argument
  * is set to be the size of a specific chunk we are testing.
@@ -2880,6 +2894,13 @@ sctp_disposition_t sctp_sf_eat_sack_6_2(const struct sctp_endpoint *ep,
 		return SCTP_DISPOSITION_DISCARD;
 	}
 
+	/* If Cumulative TSN Ack beyond the max tsn currently
+	 * send, terminating the association and respond to the
+	 * sender with an ABORT.
+	 */
+	if (!TSN_lt(ctsn, asoc->next_tsn))
+		return sctp_sf_violation_ctsn(ep, asoc, type, arg, commands);
+
 	/* Return this SACK for further processing.  */
 	sctp_add_cmd_sf(commands, SCTP_CMD_PROCESS_SACK, SCTP_SACKH(sackh));
 
@@ -3691,40 +3712,21 @@ sctp_disposition_t sctp_sf_violation(const struct sctp_endpoint *ep,
 	return SCTP_DISPOSITION_VIOLATION;
 }
 
-
 /*
- * Handle a protocol violation when the chunk length is invalid.
- * "Invalid" length is identified as smaller then the minimal length a
- * given chunk can be.  For example, a SACK chunk has invalid length
- * if it's length is set to be smaller then the size of sctp_sack_chunk_t.
- *
- * We inform the other end by sending an ABORT with a Protocol Violation
- * error code.
- *
- * Section: Not specified
- * Verification Tag:  Nothing to do
- * Inputs
- * (endpoint, asoc, chunk)
- *
- * Outputs
- * (reply_msg, msg_up, counters)
- *
- * Generate an  ABORT chunk and terminate the association.
+ * Common function to handle a protocol violation.
  */
-static sctp_disposition_t sctp_sf_violation_chunklen(
-				     const struct sctp_endpoint *ep,
+static sctp_disposition_t sctp_sf_abort_violation(
 				     const struct sctp_association *asoc,
-				     const sctp_subtype_t type,
 				     void *arg,
-				     sctp_cmd_seq_t *commands)
+				     sctp_cmd_seq_t *commands,
+				     const __u8 *payload,
+				     const size_t paylen)
 {
 	struct sctp_chunk *chunk =  arg;
 	struct sctp_chunk *abort = NULL;
-	char 		   err_str[]="The following chunk had invalid length:";
 
 	/* Make the abort chunk. */
-	abort = sctp_make_abort_violation(asoc, chunk, err_str,
-					  sizeof(err_str));
+	abort = sctp_make_abort_violation(asoc, chunk, payload, paylen);
 	if (!abort)
 		goto nomem;
 
@@ -3756,6 +3758,57 @@ nomem:
 	return SCTP_DISPOSITION_NOMEM;
 }
 
+/*
+ * Handle a protocol violation when the chunk length is invalid.
+ * "Invalid" length is identified as smaller then the minimal length a
+ * given chunk can be.  For example, a SACK chunk has invalid length
+ * if it's length is set to be smaller then the size of sctp_sack_chunk_t.
+ *
+ * We inform the other end by sending an ABORT with a Protocol Violation
+ * error code.
+ *
+ * Section: Not specified
+ * Verification Tag:  Nothing to do
+ * Inputs
+ * (endpoint, asoc, chunk)
+ *
+ * Outputs
+ * (reply_msg, msg_up, counters)
+ *
+ * Generate an  ABORT chunk and terminate the association.
+ */
+static sctp_disposition_t sctp_sf_violation_chunklen(
+				     const struct sctp_endpoint *ep,
+				     const struct sctp_association *asoc,
+				     const sctp_subtype_t type,
+				     void *arg,
+				     sctp_cmd_seq_t *commands)
+{
+	char err_str[]="The following chunk had invalid length:";
+
+	return sctp_sf_abort_violation(asoc, arg, commands, err_str,
+					sizeof(err_str));
+}
+
+/* Handle a protocol violation when the peer trying to advance the
+ * cumulative tsn ack to a point beyond the max tsn currently sent.
+ *
+ * We inform the other end by sending an ABORT with a Protocol Violation
+ * error code.
+ */
+static sctp_disposition_t sctp_sf_violation_ctsn(
+				     const struct sctp_endpoint *ep,
+				     const struct sctp_association *asoc,
+				     const sctp_subtype_t type,
+				     void *arg,
+				     sctp_cmd_seq_t *commands)
+{
+	char err_str[]="The cumulative tsn ack beyond the max tsn currently sent:";
+
+	return sctp_sf_abort_violation(asoc, arg, commands, err_str,
+					sizeof(err_str));
+}
+
 /***************************************************************************
  * These are the state functions for handling primitive (Section 10) events.
  ***************************************************************************/