sctp: fix panic when T4-rto timer expire on removed transport

If T4-rto timer is expired on a removed transport, kernel panic
will occur when we do failure management on that transport.
You can reproduce this use the following sequence:

Endpoint A                           Endpoint B
(ESTABLISHED)                        (ESTABLISHED)

            <-----------------      ASCONF
                                    (SRC=X)
ASCONF        ----------------->
(Delete IP Address = X)
            <-----------------      ASCONF-ACK
                                    (Success Indication)
            <-----------------      ASCONF
                                    (T4-rto timer expire)

This patch fixed the problem.

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

1 files changed, 3 insertions, 1 deletions

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 10abc07d42cb..7288192f7df5 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -5475,7 +5475,9 @@ sctp_disposition_t sctp_sf_t4_timer_expire(
          * detection on the appropriate destination address as defined in
          * RFC2960 [5] section 8.1 and 8.2.
          */
-        sctp_add_cmd_sf(commands, SCTP_CMD_STRIKE, SCTP_TRANSPORT(transport));
+        if (transport)
+                sctp_add_cmd_sf(commands, SCTP_CMD_STRIKE,
+                                SCTP_TRANSPORT(transport));
 
         /* Reconfig T4 timer and transport. */
         sctp_add_cmd_sf(commands, SCTP_CMD_SETUP_T4, SCTP_CHUNK(chunk));