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Subject[patch 55/56] sctp: Fix another socket race during accept/peeloff
2.6.27-stable review patch.  If anyone has any objections, please let us know.

From: Vlad Yasevich <>

commit ae53b5bd77719fed58086c5be60ce4f22bffe1c6 upstream.

There is a race between sctp_rcv() and sctp_accept() where we
have moved the association from the listening socket to the
accepted socket, but sctp_rcv() processing cached the old
socket and continues to use it.

The easy solution is to check for the socket mismatch once we've
grabed the socket lock. If we hit a mis-match, that means
that were are currently holding the lock on the listening socket,
but the association is refrencing a newly accepted socket. We need
to drop the lock on the old socket and grab the lock on the new one.

A more proper solution might be to create accepted sockets when
the new association is established, similar to TCP. That would
eliminate the race for 1-to-1 style sockets, but it would still
existing for 1-to-many sockets where a user wished to peeloff an
association. For now, we'll live with this easy solution as
it addresses the problem.

Reported-by: Michal Hocko <>
Reported-by: Karsten Keil <>
Signed-off-by: Vlad Yasevich <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>

net/sctp/input.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -249,6 +249,19 @@ int sctp_rcv(struct sk_buff *skb)

+ if (sk != rcvr->sk) {
+ /* Our cached sk is different from the rcvr->sk. This is
+ * because migrate()/accept() may have moved the association
+ * to a new socket and released all the sockets. So now we
+ * are holding a lock on the old socket while the user may
+ * be doing something with the new socket. Switch our veiw
+ * of the current sk.
+ */
+ sctp_bh_unlock_sock(sk);
+ sk = rcvr->sk;
+ sctp_bh_lock_sock(sk);
+ }
if (sock_owned_by_user(sk)) {
sctp_add_backlog(sk, skb);

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