This combines two upstream commits to fix an OOPS with
AF_UNIX and SELINUX.

basically, sk->sk_socket can become null because we access
a peer socket without any locking, so it can be shut down and
released in another thread.

Commit: d410b81b4eef2e4409f9c38ef201253fbbcc7d94
[AF_UNIX]: Make socket locking much less confusing.

The unix_state_*() locking macros imply that there is some
rwlock kind of thing going on, but the implementation is
actually a spinlock which makes the code more confusing than
it needs to be.

So use plain unix_state_lock and unix_state_unlock.
Signed-off-by: David S. Miller <davem@davemloft.net>

Commit: 19fec3e807a487415e77113cb9dbdaa2da739836
[AF_UNIX]: Fix datagram connect race causing an OOPS.

Based upon an excellent bug report and initial patch by
Frederik Deweerdt.

The UNIX datagram connect code blindly dereferences other->sk_socket
via the call down to the security_unix_may_send() function.

Without locking 'other' that pointer can go NULL via unix_release_sock()
which does sock_orphan() which also marks the socket SOCK_DEAD.

So we have to lock both 'sk' and 'other' yet avoid all kinds of
potential deadlocks (connect to self is OK for datagram sockets and it
is possible for two datagram sockets to perform a simultaneous connect
to each other).  So what we do is have a "double lock" function similar
to how we handle this situation in other areas of the kernel.  We take
the lock of the socket pointer with the smallest address first in
order to avoid ABBA style deadlocks.

Once we have them both locked, we check to see if SOCK_DEAD is set
for 'other' and if so, drop everything and retry the lookup.
Signed-off-by: David S. Miller <davem@davemloft.net>
[chrisw: backport to 2.6.20]
Signed-off-by: Chris Wright <chrisw@sous-sol.org>