Commit:     3c0d2f3780fc94746c4842e965bd2570e2119bb6
Parent:     c764c9ade6d9b710bad2b9c631ede9864333b98c
Author:     Miklos Szeredi <[EMAIL PROTECTED]>
AuthorDate: Tue Jun 5 13:10:29 2007 -0700
Committer:  David S. Miller <[EMAIL PROTECTED]>
CommitDate: Thu Jun 7 13:40:44 2007 -0700

    [AF_UNIX]: Fix stream recvmsg() race.
    A recv() on an AF_UNIX, SOCK_STREAM socket can race with a
    send()+close() on the peer, causing recv() to return zero, even though
    the sent data should be received.
    This happens if the send() and the close() is performed between
    skb_dequeue() and checking sk->sk_shutdown in unix_stream_recvmsg():
    process A  skb_dequeue() returns NULL, there's no data in the socket queue
    process B  new data is inserted onto the queue by unix_stream_sendmsg()
    process B  sk->sk_shutdown is set to SHUTDOWN_MASK by unix_release_sock()
    process A  sk->sk_shutdown is checked, unix_release_sock() returns zero
    I'm surprised nobody noticed this, it's not hard to trigger.  Maybe
    it's just (un)luck with the timing.
    It's possible to work around this bug in userspace, by retrying the
    recv() once in case of a zero return value.
    Signed-off-by: Miklos Szeredi <[EMAIL PROTECTED]>
    Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
 net/unix/af_unix.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 87c794d..d70fa30 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1744,20 +1744,23 @@ static int unix_stream_recvmsg(struct kiocb *iocb, 
struct socket *sock,
                int chunk;
                struct sk_buff *skb;
+               unix_state_lock(sk);
                skb = skb_dequeue(&sk->sk_receive_queue);
                if (skb==NULL)
                        if (copied >= target)
-                               break;
+                               goto unlock;
                         *      POSIX 1003.1g mandates this order.
                        if ((err = sock_error(sk)) != 0)
-                               break;
+                               goto unlock;
                        if (sk->sk_shutdown & RCV_SHUTDOWN)
-                               break;
+                               goto unlock;
+                       unix_state_unlock(sk);
                        err = -EAGAIN;
                        if (!timeo)
@@ -1771,7 +1774,11 @@ static int unix_stream_recvmsg(struct kiocb *iocb, 
struct socket *sock,
+ unlock:
+                       unix_state_unlock(sk);
+                       break;
+               unix_state_unlock(sk);
                if (check_creds) {
                        /* Never glue messages from different writers */
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