2013-04-11 20:49:00

by Steven Rostedt

[permalink] [raw]
Subject: [ 154/171 ] unix: fix a race condition in unix_release() stable review patch.
If anyone has any objections, please let me know.


From: Paul Moore <[email protected]>

[ 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 <[email protected]>
Signed-off-by: Paul Moore <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
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 c5ee4ff..1b3abc8 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -384,7 +384,7 @@ 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 path path;
@@ -453,8 +453,6 @@ static int unix_release_sock(struct sock *sk, int embrion)

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

static void init_peercred(struct sock *sk)
@@ -704,9 +702,10 @@ 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)