[PATCH] Fix AF_UNIX OOPS

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>

include/net/af_unix.h

@@ -62,13 +62,11 @@ struct unix_skb_parms {
 #define UNIXCREDS(skb)	(&UNIXCB((skb)).creds)
 #define UNIXSID(skb)	(&UNIXCB((skb)).secid)
 
-#define unix_state_rlock(s)	spin_lock(&unix_sk(s)->lock)
-#define unix_state_runlock(s)	spin_unlock(&unix_sk(s)->lock)
-#define unix_state_wlock(s)	spin_lock(&unix_sk(s)->lock)
-#define unix_state_wlock_nested(s) \
+#define unix_state_lock(s)	spin_lock(&unix_sk(s)->lock)
+#define unix_state_unlock(s)	spin_unlock(&unix_sk(s)->lock)
+#define unix_state_lock_nested(s) \
 				spin_lock_nested(&unix_sk(s)->lock, \
 				SINGLE_DEPTH_NESTING)
-#define unix_state_wunlock(s)	spin_unlock(&unix_sk(s)->lock)
 
 #ifdef __KERNEL__
 /* The AF_UNIX socket */

net/unix/af_unix.c

@@ -175,11 +175,11 @@ static struct sock *unix_peer_get(struct sock *s)
 {
 	struct sock *peer;
 
-	unix_state_rlock(s);
+	unix_state_lock(s);
 	peer = unix_peer(s);
 	if (peer)
 		sock_hold(peer);
-	unix_state_runlock(s);
+	unix_state_unlock(s);
 	return peer;
 }
 
@@ -370,7 +370,7 @@ static int unix_release_sock (struct sock *sk, int embrion)
 	unix_remove_socket(sk);
 
 	/* Clear state */
-	unix_state_wlock(sk);
+	unix_state_lock(sk);
 	sock_orphan(sk);
 	sk->sk_shutdown = SHUTDOWN_MASK;
 	dentry	     = u->dentry;
@@ -379,7 +379,7 @@ static int unix_release_sock (struct sock *sk, int embrion)
 	u->mnt	     = NULL;
 	state = sk->sk_state;
 	sk->sk_state = TCP_CLOSE;
-	unix_state_wunlock(sk);
+	unix_state_unlock(sk);
 
 	wake_up_interruptible_all(&u->peer_wait);
 
@@ -387,12 +387,12 @@ static int unix_release_sock (struct sock *sk, int embrion)
 
 	if (skpair!=NULL) {
 		if (sk->sk_type == SOCK_STREAM || sk->sk_type == SOCK_SEQPACKET) {
-			unix_state_wlock(skpair);
+			unix_state_lock(skpair);
 			/* No more writes */
 			skpair->sk_shutdown = SHUTDOWN_MASK;
 			if (!skb_queue_empty(&sk->sk_receive_queue) || embrion)
 				skpair->sk_err = ECONNRESET;
-			unix_state_wunlock(skpair);
+			unix_state_unlock(skpair);
 			skpair->sk_state_change(skpair);
 			read_lock(&skpair->sk_callback_lock);
 			sk_wake_async(skpair,1,POLL_HUP);
@@ -449,7 +449,7 @@ static int unix_listen(struct socket *sock, int backlog)
 	err = -EINVAL;
 	if (!u->addr)
 		goto out;			/* No listens on an unbound socket */
-	unix_state_wlock(sk);
+	unix_state_lock(sk);
 	if (sk->sk_state != TCP_CLOSE && sk->sk_state != TCP_LISTEN)
 		goto out_unlock;
 	if (backlog > sk->sk_max_ack_backlog)
@@ -463,7 +463,7 @@ static int unix_listen(struct socket *sock, int backlog)
 	err = 0;
 
 out_unlock:
-	unix_state_wunlock(sk);
+	unix_state_unlock(sk);
 out:
 	return err;
 }
@@ -859,6 +859,31 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	goto out_up;
 }
 
+static void unix_state_double_lock(struct sock *sk1, struct sock *sk2)
+{
+	if (unlikely(sk1 == sk2) || !sk2) {
+		unix_state_lock(sk1);
+		return;
+	}
+	if (sk1 < sk2) {
+		unix_state_lock(sk1);
+		unix_state_lock_nested(sk2);
+	} else {
+		unix_state_lock(sk2);
+		unix_state_lock_nested(sk1);
+	}
+}
+
+static void unix_state_double_unlock(struct sock *sk1, struct sock *sk2)
+{
+	if (unlikely(sk1 == sk2) || !sk2) {
+		unix_state_unlock(sk1);
+		return;
+	}
+	unix_state_unlock(sk1);
+	unix_state_unlock(sk2);
+}
+
 static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 			      int alen, int flags)
 {
@@ -878,11 +903,19 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 		    !unix_sk(sk)->addr && (err = unix_autobind(sock)) != 0)
 			goto out;
 
+restart:
 		other=unix_find_other(sunaddr, alen, sock->type, hash, &err);
 		if (!other)
 			goto out;
 
-		unix_state_wlock(sk);
+		unix_state_double_lock(sk, other);
+
+		/* Apparently VFS overslept socket death. Retry. */
+		if (sock_flag(other, SOCK_DEAD)) {
+			unix_state_double_unlock(sk, other);
+			sock_put(other);
+			goto restart;
+		}
 
 		err = -EPERM;
 		if (!unix_may_send(sk, other))
@@ -897,7 +930,7 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 		 *	1003.1g breaking connected state with AF_UNSPEC
 		 */
 		other = NULL;
-		unix_state_wlock(sk);
+		unix_state_double_lock(sk, other);
 	}
 
 	/*
@@ -906,19 +939,19 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 	if (unix_peer(sk)) {
 		struct sock *old_peer = unix_peer(sk);
 		unix_peer(sk)=other;
-		unix_state_wunlock(sk);
+		unix_state_double_unlock(sk, other);
 
 		if (other != old_peer)
 			unix_dgram_disconnected(sk, old_peer);
 		sock_put(old_peer);
 	} else {
 		unix_peer(sk)=other;
-		unix_state_wunlock(sk);
+		unix_state_double_unlock(sk, other);
 	}
  	return 0;
 
 out_unlock:
-	unix_state_wunlock(sk);
+	unix_state_double_unlock(sk, other);
 	sock_put(other);
 out:
 	return err;
@@ -937,7 +970,7 @@ static long unix_wait_for_peer(struct sock *other, long timeo)
 		(skb_queue_len(&other->sk_receive_queue) >
 		 other->sk_max_ack_backlog);
 
-	unix_state_runlock(other);
+	unix_state_unlock(other);
 
 	if (sched)
 		timeo = schedule_timeout(timeo);
@@ -995,11 +1028,11 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 		goto out;
 
 	/* Latch state of peer */
-	unix_state_rlock(other);
+	unix_state_lock(other);
 
 	/* Apparently VFS overslept socket death. Retry. */
 	if (sock_flag(other, SOCK_DEAD)) {
-		unix_state_runlock(other);
+		unix_state_unlock(other);
 		sock_put(other);
 		goto restart;
 	}
@@ -1049,18 +1082,18 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 		goto out_unlock;
 	}
 
-	unix_state_wlock_nested(sk);
+	unix_state_lock_nested(sk);
 
 	if (sk->sk_state != st) {
-		unix_state_wunlock(sk);
-		unix_state_runlock(other);
+		unix_state_unlock(sk);
+		unix_state_unlock(other);
 		sock_put(other);
 		goto restart;
 	}
 
 	err = security_unix_stream_connect(sock, other->sk_socket, newsk);
 	if (err) {
-		unix_state_wunlock(sk);
+		unix_state_unlock(sk);
 		goto out_unlock;
 	}
 
@@ -1097,7 +1130,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	smp_mb__after_atomic_inc();	/* sock_hold() does an atomic_inc() */
 	unix_peer(sk)	= newsk;
 
-	unix_state_wunlock(sk);
+	unix_state_unlock(sk);
 
 	/* take ten and and send info to listening sock */
 	spin_lock(&other->sk_receive_queue.lock);
@@ -1106,14 +1139,14 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	 * is installed to listening socket. */
 	atomic_inc(&newu->inflight);
 	spin_unlock(&other->sk_receive_queue.lock);
-	unix_state_runlock(other);
+	unix_state_unlock(other);
 	other->sk_data_ready(other, 0);
 	sock_put(other);
 	return 0;
 
 out_unlock:
 	if (other)
-		unix_state_runlock(other);
+		unix_state_unlock(other);
 
 out:
 	if (skb)
@@ -1179,10 +1212,10 @@ static int unix_accept(struct socket *sock, struct socket *newsock, int flags)
 	wake_up_interruptible(&unix_sk(sk)->peer_wait);
 
 	/* attach accepted sock to socket */
-	unix_state_wlock(tsk);
+	unix_state_lock(tsk);
 	newsock->state = SS_CONNECTED;
 	sock_graft(tsk, newsock);
-	unix_state_wunlock(tsk);
+	unix_state_unlock(tsk);
 	return 0;
 
 out:
@@ -1209,7 +1242,7 @@ static int unix_getname(struct socket *sock, struct sockaddr *uaddr, int *uaddr_
 	}
 
 	u = unix_sk(sk);
-	unix_state_rlock(sk);
+	unix_state_lock(sk);
 	if (!u->addr) {
 		sunaddr->sun_family = AF_UNIX;
 		sunaddr->sun_path[0] = 0;
@@ -1220,7 +1253,7 @@ static int unix_getname(struct socket *sock, struct sockaddr *uaddr, int *uaddr_
 		*uaddr_len = addr->len;
 		memcpy(sunaddr, addr->name, *uaddr_len);
 	}
-	unix_state_runlock(sk);
+	unix_state_unlock(sk);
 	sock_put(sk);
 out:
 	return err;
@@ -1338,7 +1371,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 			goto out_free;
 	}
 
-	unix_state_rlock(other);
+	unix_state_lock(other);
 	err = -EPERM;
 	if (!unix_may_send(sk, other))
 		goto out_unlock;
@@ -1348,20 +1381,20 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		 *	Check with 1003.1g - what should
 		 *	datagram error
 		 */
-		unix_state_runlock(other);
+		unix_state_unlock(other);
 		sock_put(other);
 
 		err = 0;
-		unix_state_wlock(sk);
+		unix_state_lock(sk);
 		if (unix_peer(sk) == other) {
 			unix_peer(sk)=NULL;
-			unix_state_wunlock(sk);
+			unix_state_unlock(sk);
 
 			unix_dgram_disconnected(sk, other);
 			sock_put(other);
 			err = -ECONNREFUSED;
 		} else {
-			unix_state_wunlock(sk);
+			unix_state_unlock(sk);
 		}
 
 		other = NULL;
@@ -1398,14 +1431,14 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	}
 
 	skb_queue_tail(&other->sk_receive_queue, skb);
-	unix_state_runlock(other);
+	unix_state_unlock(other);
 	other->sk_data_ready(other, len);
 	sock_put(other);
 	scm_destroy(siocb->scm);
 	return len;
 
 out_unlock:
-	unix_state_runlock(other);
+	unix_state_unlock(other);
 out_free:
 	kfree_skb(skb);
 out:
@@ -1495,14 +1528,14 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 			goto out_err;
 		}
 
-		unix_state_rlock(other);
+		unix_state_lock(other);
 
 		if (sock_flag(other, SOCK_DEAD) ||
 		    (other->sk_shutdown & RCV_SHUTDOWN))
 			goto pipe_err_free;
 
 		skb_queue_tail(&other->sk_receive_queue, skb);
-		unix_state_runlock(other);
+		unix_state_unlock(other);
 		other->sk_data_ready(other, size);
 		sent+=size;
 	}
@@ -1513,7 +1546,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	return sent;
 
 pipe_err_free:
-	unix_state_runlock(other);
+	unix_state_unlock(other);
 	kfree_skb(skb);
 pipe_err:
 	if (sent==0 && !(msg->msg_flags&MSG_NOSIGNAL))
@@ -1642,7 +1675,7 @@ static long unix_stream_data_wait(struct sock * sk, long timeo)
 {
 	DEFINE_WAIT(wait);
 
-	unix_state_rlock(sk);
+	unix_state_lock(sk);
 
 	for (;;) {
 		prepare_to_wait(sk->sk_sleep, &wait, TASK_INTERRUPTIBLE);
@@ -1655,14 +1688,14 @@ static long unix_stream_data_wait(struct sock * sk, long timeo)
 			break;
 
 		set_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags);
-		unix_state_runlock(sk);
+		unix_state_unlock(sk);
 		timeo = schedule_timeout(timeo);
-		unix_state_rlock(sk);
+		unix_state_lock(sk);
 		clear_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags);
 	}
 
 	finish_wait(sk->sk_sleep, &wait);
-	unix_state_runlock(sk);
+	unix_state_unlock(sk);
 	return timeo;
 }
 
@@ -1817,12 +1850,12 @@ static int unix_shutdown(struct socket *sock, int mode)
 	mode = (mode+1)&(RCV_SHUTDOWN|SEND_SHUTDOWN);
 
 	if (mode) {
-		unix_state_wlock(sk);
+		unix_state_lock(sk);
 		sk->sk_shutdown |= mode;
 		other=unix_peer(sk);
 		if (other)
 			sock_hold(other);
-		unix_state_wunlock(sk);
+		unix_state_unlock(sk);
 		sk->sk_state_change(sk);
 
 		if (other &&
@@ -1834,9 +1867,9 @@ static int unix_shutdown(struct socket *sock, int mode)
 				peer_mode |= SEND_SHUTDOWN;
 			if (mode&SEND_SHUTDOWN)
 				peer_mode |= RCV_SHUTDOWN;
-			unix_state_wlock(other);
+			unix_state_lock(other);
 			other->sk_shutdown |= peer_mode;
-			unix_state_wunlock(other);
+			unix_state_unlock(other);
 			other->sk_state_change(other);
 			read_lock(&other->sk_callback_lock);
 			if (peer_mode == SHUTDOWN_MASK)
@@ -1974,7 +2007,7 @@ static int unix_seq_show(struct seq_file *seq, void *v)
 	else {
 		struct sock *s = v;
 		struct unix_sock *u = unix_sk(s);
-		unix_state_rlock(s);
+		unix_state_lock(s);
 
 		seq_printf(seq, "%p: %08X %08X %08X %04X %02X %5lu",
 			s,
@@ -2002,7 +2035,7 @@ static int unix_seq_show(struct seq_file *seq, void *v)
 			for ( ; i < len; i++)
 				seq_putc(seq, u->addr->name->sun_path[i]);
 		}
-		unix_state_runlock(s);
+		unix_state_unlock(s);
 		seq_putc(seq, '\n');
 	}