sctp: deal with multiple COOKIE_ECHO chunks

Attempt to reduce the number of IP packets emitted in response to single
SCTP packet (2e3216cd) introduced a complication - if a packet contains
two COOKIE_ECHO chunks and nothing else then SCTP state machine corks the
socket while processing first COOKIE_ECHO and then loses the association
and forgets to uncork the socket. To deal with the issue add new SCTP
command which can be used to set association explictly. Use this new
command when processing second COOKIE_ECHO chunk to restore the context
for SCTP state machine.
Signed-off-by: Max Matveev <makc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/command.h

@@ -109,6 +109,7 @@ typedef enum {
 	SCTP_CMD_SEND_MSG,	 /* Send the whole use message */
 	SCTP_CMD_SEND_NEXT_ASCONF, /* Send the next ASCONF after ACK */
 	SCTP_CMD_PURGE_ASCONF_QUEUE, /* Purge all asconf queues.*/
+	SCTP_CMD_SET_ASOC,	 /* Restore association context */
 	SCTP_CMD_LAST
 } sctp_verb_t;
 

net/sctp/sm_sideeffect.c

@@ -1689,6 +1689,11 @@ static int sctp_cmd_interpreter(sctp_event_t event_type,
 		case SCTP_CMD_PURGE_ASCONF_QUEUE:
 			sctp_asconf_queue_teardown(asoc);
 			break;
+
+		case SCTP_CMD_SET_ASOC:
+			asoc = cmd->obj.asoc;
+			break;
+
 		default:
 			pr_warn("Impossible command: %u, %p\n",
 				cmd->verb, cmd->obj.ptr);

net/sctp/sm_statefuns.c

@@ -2047,6 +2047,12 @@ sctp_disposition_t sctp_sf_do_5_2_4_dupcook(const struct sctp_endpoint *ep,
 	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_ASOC, SCTP_ASOC(new_asoc));
 	sctp_add_cmd_sf(commands, SCTP_CMD_DELETE_TCB, SCTP_NULL());
 
+	/* Restore association pointer to provide SCTP command interpeter
+	 * with a valid context in case it needs to manipulate
+	 * the queues */
+	sctp_add_cmd_sf(commands, SCTP_CMD_SET_ASOC,
+			 SCTP_ASOC((struct sctp_association *)asoc));
+
 	return retval;
 
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