sctp: do not update a_rwnd if we are not issuing a sack

The SACK can be lost pretty much elsewhere, but if its allocation fail,
we know we are not sending it, so it is better to revert a_rwnd to its
previous value as this may give it a chance to issue a window update
later.

Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 1 deletions

diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index 3c22c41a2bc2..7fe56d0acabf 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -215,10 +215,14 @@ static int sctp_gen_sack(struct sctp_association *asoc, int force,
                 sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_RESTART,
                                 SCTP_TO(SCTP_EVENT_TIMEOUT_SACK));
         } else {
+                __u32 old_a_rwnd = asoc->a_rwnd;
+
                 asoc->a_rwnd = asoc->rwnd;
                 sack = sctp_make_sack(asoc);
-                if (!sack)
+                if (!sack) {
+                        asoc->a_rwnd = old_a_rwnd;
                         goto nomem;
+                }
 
                 asoc->peer.sack_needed = 0;
                 asoc->peer.sack_cnt = 0;