sctp: fix an issue that plpmtu can never go to complete state

commit 6ca328e985cd995dfd1d5de44046e6074f853fbb upstream.

When doing plpmtu probe, the probe size is growing every time when it
receives the ACK during the Search state until the probe fails. When
the failure occurs, pl.probe_high is set and it goes to the Complete
state.

However, if the link pmtu is huge, like 65535 in loopback_dev, the probe
eventually keeps using SCTP_MAX_PLPMTU as the probe size and never fails.
Because of that, pl.probe_high can not be set, and the plpmtu probe can
never go to the Complete state.

Fix it by setting pl.probe_high to SCTP_MAX_PLPMTU when the probe size
grows to SCTP_MAX_PLPMTU in sctp_transport_pl_recv(). Also, not allow
the probe size greater than SCTP_MAX_PLPMTU in the Complete state.

Fixes: b87641aff9e7 ("sctp: do state transition when a probe succeeds on HB ACK recv path")
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index b3f1a91e9a079c7a96188a9740bf2a7e8cfac7b7..2990365c2f2c9dd07ee81d796ffa6d5a96bde17d 100644 (file)
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -324,9 +324,12 @@ bool sctp_transport_pl_recv(struct sctp_transport *t)
                t->pl.probe_size += SCTP_PL_BIG_STEP;
        } else if (t->pl.state == SCTP_PL_SEARCH) {
                if (!t->pl.probe_high) {
-                       t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
-                                              SCTP_MAX_PLPMTU);
-                       return false;
+                       if (t->pl.probe_size < SCTP_MAX_PLPMTU) {
+                               t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_BIG_STEP,
+                                                      SCTP_MAX_PLPMTU);
+                               return false;
+                       }
+                       t->pl.probe_high = SCTP_MAX_PLPMTU;
                }
                t->pl.probe_size += SCTP_PL_MIN_STEP;
                if (t->pl.probe_size >= t->pl.probe_high) {
@@ -341,7 +344,7 @@ bool sctp_transport_pl_recv(struct sctp_transport *t)
        } else if (t->pl.state == SCTP_PL_COMPLETE) {
                /* Raise probe_size again after 30 * interval in Search Complete */
                t->pl.state = SCTP_PL_SEARCH; /* Search Complete -> Search */
-               t->pl.probe_size += SCTP_PL_MIN_STEP;
+               t->pl.probe_size = min(t->pl.probe_size + SCTP_PL_MIN_STEP, SCTP_MAX_PLPMTU);
        }
 
        return t->pl.state == SCTP_PL_COMPLETE;