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unix: fix a race condition in unix_release()

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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
problem.

Reported-by: Jan Stancek <jan.stancek@gmail.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paul Moore 2013-03-25 03:18:33 +00:00 • committed by David S. Miller
parent 7ebe183c6d
commit ded34e0fe8
1 changed files with 3 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

7
net/unix/af_unix.c
View file

@ -382,7 +382,7 @@ static void unix_sock_destructor(struct sock *sk)
#endif #endif
} }
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 unix_sock *u = unix_sk(sk);
struct path path; struct path path;
@ -451,8 +451,6 @@ static int unix_release_sock(struct sock *sk, int embrion)
if (unix_tot_inflight) if (unix_tot_inflight)
unix_gc(); /* Garbage collect fds */ unix_gc(); /* Garbage collect fds */
return 0;
} }
static void init_peercred(struct sock *sk) static void init_peercred(struct sock *sk)
@ -699,9 +697,10 @@ static int unix_release(struct socket *sock)
if (!sk) if (!sk)
return 0; return 0;
unix_release_sock(sk, 0);
sock->sk = NULL; sock->sk = NULL;
return unix_release_sock(sk, 0); return 0;
} }
static int unix_autobind(struct socket *sock) static int unix_autobind(struct socket *sock)