sctp: fix the transport dead race check by using atomic_add_unless on refcnt

Now when __sctp_lookup_association is running in BH, it will try to
check if t->dead is set, but meanwhile other CPUs may be freeing this
transport and this assoc and if it happens that
__sctp_lookup_association checked t->dead a bit too early, it may think
that the association is still good while it was already freed.

So we fix this race by using atomic_add_unless in sctp_transport_hold.
After we get one transport from hashtable, we will hold it only when
this transport's refcnt is not 0, so that we can make sure t->asoc
cannot be freed before we hold the asoc again.

Note that sctp association is not freed using RCU so we can't use
atomic_add_unless() with it as it may just be too late for that either.

Fixes: 4f0087812648 ("sctp: apply rhashtable api to send/recv path")
Reported-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 20e72129be1c..344da04e2e30 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -955,7 +955,7 @@ void sctp_transport_route(struct sctp_transport *, union sctp_addr *,
 void sctp_transport_pmtu(struct sctp_transport *, struct sock *sk);
 void sctp_transport_free(struct sctp_transport *);
 void sctp_transport_reset_timers(struct sctp_transport *);
-void sctp_transport_hold(struct sctp_transport *);
+int sctp_transport_hold(struct sctp_transport *);
 void sctp_transport_put(struct sctp_transport *);
 void sctp_transport_update_rto(struct sctp_transport *, __u32);
 void sctp_transport_raise_cwnd(struct sctp_transport *, __u32, __u32);