[ 161/184] unix: fix a race condition in unix_release()

From: Willy Tarreau
Date: Tue Jun 04 2013 - 18:58:45 EST

2.6.32-longterm review patch. If anyone has any objections, please let me know.


From: Paul Moore <pmoore@xxxxxxxxxx>

[ Upstream commit ded34e0fe8fe8c2d595bfa30626654e4b87621e0 ]

As reported by Jan, and others over the past few years, there is a
race condition caused by unix_release setting the sock->sk pointer
to NULL before properly marking the socket as dead/orphaned. This
can cause a problem with the LSM hook security_unix_may_send() if
there is another socket attempting to write to this partially
released socket in between when sock->sk is set to NULL and it is
marked as dead/orphaned. This patch fixes this by only setting
sock->sk to NULL after the socket has been marked as dead; I also
take the opportunity to make unix_release_sock() a void function
as it only ever returned 0/success.

Dave, I think this one should go on the -stable pile.

Special thanks to Jan for coming up with a reproducer for this

Reported-by: Jan Stancek <jan.stancek@xxxxxxxxx>
Signed-off-by: Paul Moore <pmoore@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
net/unix/af_unix.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index db8d51a..d146b76 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -370,7 +370,7 @@ static void unix_sock_destructor(struct sock *sk)

-static int unix_release_sock(struct sock *sk, int embrion)
+static void unix_release_sock(struct sock *sk, int embrion)
struct unix_sock *u = unix_sk(sk);
struct dentry *dentry;
@@ -445,8 +445,6 @@ static int unix_release_sock(struct sock *sk, int embrion)

if (unix_tot_inflight)
unix_gc(); /* Garbage collect fds */
- return 0;

static int unix_listen(struct socket *sock, int backlog)
@@ -660,9 +658,10 @@ static int unix_release(struct socket *sock)
if (!sk)
return 0;

+ unix_release_sock(sk, 0);
sock->sk = NULL;

- return unix_release_sock(sk, 0);
+ return 0;

static int unix_autobind(struct socket *sock)

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