Merge branch 'af_unix-fix-lockless-access-of-sk-sk_state-and-others-fields'

Kuniyuki Iwashima says:

====================
af_unix: Fix lockless access of sk->sk_state and others fields.

The patch 1 fixes a bug where SOCK_DGRAM's sk->sk_state is changed
to TCP_CLOSE even if the socket is connect()ed to another socket.

The rest of this series annotates lockless accesses to the following
fields.

  * sk->sk_state
  * sk->sk_sndbuf
  * net->unx.sysctl_max_dgram_qlen
  * sk->sk_receive_queue.qlen
  * sk->sk_shutdown

Note that with this series there is skb_queue_empty() left in
unix_dgram_disconnected() that needs to be changed to lockless
version, and unix_peer(other) access there should be protected
by unix_state_lock().

This will require some refactoring, so another series will follow.

Changes:
  v2:
    * Patch 1: Fix wrong double lock

  v1: https://lore.kernel.org/netdev/20240603143231.62085-1-kuniyu@amazon.com/
====================

Link: https://lore.kernel.org/r/20240604165241.44758-1-kuniyu@amazon.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/unix/af_unix.c

@@ -221,15 +221,9 @@ static inline int unix_may_send(struct sock *sk, struct sock *osk)
 	return unix_peer(osk) == NULL || unix_our_peer(sk, osk);
 }
 
-static inline int unix_recvq_full(const struct sock *sk)
-{
-	return skb_queue_len(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
-}
-
 static inline int unix_recvq_full_lockless(const struct sock *sk)
 {
-	return skb_queue_len_lockless(&sk->sk_receive_queue) >
-		READ_ONCE(sk->sk_max_ack_backlog);
+	return skb_queue_len_lockless(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
 }
 
 struct sock *unix_peer_get(struct sock *s)
@@ -530,10 +524,10 @@ static int unix_dgram_peer_wake_me(struct sock *sk, struct sock *other)
 	return 0;
 }
 
-static int unix_writable(const struct sock *sk)
+static int unix_writable(const struct sock *sk, unsigned char state)
 {
-	return sk->sk_state != TCP_LISTEN &&
-	       (refcount_read(&sk->sk_wmem_alloc) << 2) <= sk->sk_sndbuf;
+	return state != TCP_LISTEN &&
+		(refcount_read(&sk->sk_wmem_alloc) << 2) <= READ_ONCE(sk->sk_sndbuf);
 }
 
 static void unix_write_space(struct sock *sk)
@@ -541,7 +535,7 @@ static void unix_write_space(struct sock *sk)
 	struct socket_wq *wq;
 
 	rcu_read_lock();
-	if (unix_writable(sk)) {
+	if (unix_writable(sk, READ_ONCE(sk->sk_state))) {
 		wq = rcu_dereference(sk->sk_wq);
 		if (skwq_has_sleeper(wq))
 			wake_up_interruptible_sync_poll(&wq->wait,
@@ -570,7 +564,6 @@ static void unix_dgram_disconnected(struct sock *sk, struct sock *other)
 			sk_error_report(other);
 		}
 	}
-	other->sk_state = TCP_CLOSE;
 }
 
 static void unix_sock_destructor(struct sock *sk)
@@ -617,7 +610,7 @@ static void unix_release_sock(struct sock *sk, int embrion)
 	u->path.dentry = NULL;
 	u->path.mnt = NULL;
 	state = sk->sk_state;
-	sk->sk_state = TCP_CLOSE;
+	WRITE_ONCE(sk->sk_state, TCP_CLOSE);
 
 	skpair = unix_peer(sk);
 	unix_peer(sk) = NULL;
@@ -638,7 +631,7 @@ static void unix_release_sock(struct sock *sk, int embrion)
 			unix_state_lock(skpair);
 			/* No more writes */
 			WRITE_ONCE(skpair->sk_shutdown, SHUTDOWN_MASK);
-			if (!skb_queue_empty(&sk->sk_receive_queue) || embrion)
+			if (!skb_queue_empty_lockless(&sk->sk_receive_queue) || embrion)
 				WRITE_ONCE(skpair->sk_err, ECONNRESET);
 			unix_state_unlock(skpair);
 			skpair->sk_state_change(skpair);
@@ -739,7 +732,8 @@ static int unix_listen(struct socket *sock, int backlog)
 	if (backlog > sk->sk_max_ack_backlog)
 		wake_up_interruptible_all(&u->peer_wait);
 	sk->sk_max_ack_backlog	= backlog;
-	sk->sk_state		= TCP_LISTEN;
+	WRITE_ONCE(sk->sk_state, TCP_LISTEN);
+
 	/* set credentials so connect can copy them */
 	init_peercred(sk);
 	err = 0;
@@ -976,7 +970,7 @@ static struct sock *unix_create1(struct net *net, struct socket *sock, int kern,
 	sk->sk_hash		= unix_unbound_hash(sk);
 	sk->sk_allocation	= GFP_KERNEL_ACCOUNT;
 	sk->sk_write_space	= unix_write_space;
-	sk->sk_max_ack_backlog	= net->unx.sysctl_max_dgram_qlen;
+	sk->sk_max_ack_backlog	= READ_ONCE(net->unx.sysctl_max_dgram_qlen);
 	sk->sk_destruct		= unix_sock_destructor;
 	u = unix_sk(sk);
 	u->listener = NULL;
@@ -1402,7 +1396,8 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 		if (err)
 			goto out_unlock;
 
-		sk->sk_state = other->sk_state = TCP_ESTABLISHED;
+		WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED);
+		WRITE_ONCE(other->sk_state, TCP_ESTABLISHED);
 	} else {
 		/*
 		 *	1003.1g breaking connected state with AF_UNSPEC
@@ -1419,13 +1414,20 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 
 		unix_peer(sk) = other;
 		if (!other)
-			sk->sk_state = TCP_CLOSE;
+			WRITE_ONCE(sk->sk_state, TCP_CLOSE);
 		unix_dgram_peer_wake_disconnect_wakeup(sk, old_peer);
 
 		unix_state_double_unlock(sk, other);
 
-		if (other != old_peer)
+		if (other != old_peer) {
 			unix_dgram_disconnected(sk, old_peer);
+
+			unix_state_lock(old_peer);
+			if (!unix_peer(old_peer))
+				WRITE_ONCE(old_peer->sk_state, TCP_CLOSE);
+			unix_state_unlock(old_peer);
+		}
+
 		sock_put(old_peer);
 	} else {
 		unix_peer(sk) = other;
@@ -1473,7 +1475,6 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	struct sk_buff *skb = NULL;
 	long timeo;
 	int err;
-	int st;
 
 	err = unix_validate_addr(sunaddr, addr_len);
 	if (err)
@@ -1538,7 +1539,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	if (other->sk_shutdown & RCV_SHUTDOWN)
 		goto out_unlock;
 
-	if (unix_recvq_full(other)) {
+	if (unix_recvq_full_lockless(other)) {
 		err = -EAGAIN;
 		if (!timeo)
 			goto out_unlock;
@@ -1563,9 +1564,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 
 	   Well, and we have to recheck the state after socket locked.
 	 */
-	st = sk->sk_state;
-
-	switch (st) {
+	switch (READ_ONCE(sk->sk_state)) {
 	case TCP_CLOSE:
 		/* This is ok... continue with connect */
 		break;
@@ -1580,7 +1579,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 
 	unix_state_lock_nested(sk, U_LOCK_SECOND);
 
-	if (sk->sk_state != st) {
+	if (sk->sk_state != TCP_CLOSE) {
 		unix_state_unlock(sk);
 		unix_state_unlock(other);
 		sock_put(other);
@@ -1633,7 +1632,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 	copy_peercred(sk, other);
 
 	sock->state	= SS_CONNECTED;
-	sk->sk_state	= TCP_ESTABLISHED;
+	WRITE_ONCE(sk->sk_state, TCP_ESTABLISHED);
 	sock_hold(newsk);
 
 	smp_mb__after_atomic();	/* sock_hold() does an atomic_inc() */
@@ -1705,7 +1704,7 @@ static int unix_accept(struct socket *sock, struct socket *newsock,
 		goto out;
 
 	arg->err = -EINVAL;
-	if (sk->sk_state != TCP_LISTEN)
+	if (READ_ONCE(sk->sk_state) != TCP_LISTEN)
 		goto out;
 
 	/* If socket state is TCP_LISTEN it cannot change (for now...),
@@ -1962,7 +1961,7 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 	}
 
 	err = -EMSGSIZE;
-	if (len > sk->sk_sndbuf - 32)
+	if (len > READ_ONCE(sk->sk_sndbuf) - 32)
 		goto out;
 
 	if (len > SKB_MAX_ALLOC) {
@@ -2044,7 +2043,7 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 			unix_peer(sk) = NULL;
 			unix_dgram_peer_wake_disconnect_wakeup(sk, other);
 
-			sk->sk_state = TCP_CLOSE;
+			WRITE_ONCE(sk->sk_state, TCP_CLOSE);
 			unix_state_unlock(sk);
 
 			unix_dgram_disconnected(sk, other);
@@ -2221,7 +2220,7 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 	}
 
 	if (msg->msg_namelen) {
-		err = sk->sk_state == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
+		err = READ_ONCE(sk->sk_state) == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
 		goto out_err;
 	} else {
 		err = -ENOTCONN;
@@ -2242,7 +2241,7 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 						   &err, 0);
 		} else {
 			/* Keep two messages in the pipe so it schedules better */
-			size = min_t(int, size, (sk->sk_sndbuf >> 1) - 64);
+			size = min_t(int, size, (READ_ONCE(sk->sk_sndbuf) >> 1) - 64);
 
 			/* allow fallback to order-0 allocations */
 			size = min_t(int, size, SKB_MAX_HEAD(0) + UNIX_SKB_FRAGS_SZ);
@@ -2335,7 +2334,7 @@ static int unix_seqpacket_sendmsg(struct socket *sock, struct msghdr *msg,
 	if (err)
 		return err;
 
-	if (sk->sk_state != TCP_ESTABLISHED)
+	if (READ_ONCE(sk->sk_state) != TCP_ESTABLISHED)
 		return -ENOTCONN;
 
 	if (msg->msg_namelen)
@@ -2349,7 +2348,7 @@ static int unix_seqpacket_recvmsg(struct socket *sock, struct msghdr *msg,
 {
 	struct sock *sk = sock->sk;
 
-	if (sk->sk_state != TCP_ESTABLISHED)
+	if (READ_ONCE(sk->sk_state) != TCP_ESTABLISHED)
 		return -ENOTCONN;
 
 	return unix_dgram_recvmsg(sock, msg, size, flags);
@@ -2654,7 +2653,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 
 static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 {
-	if (unlikely(sk->sk_state != TCP_ESTABLISHED))
+	if (unlikely(READ_ONCE(sk->sk_state) != TCP_ESTABLISHED))
 		return -ENOTCONN;
 
 	return unix_read_skb(sk, recv_actor);
@@ -2678,7 +2677,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
 	size_t size = state->size;
 	unsigned int last_len;
 
-	if (unlikely(sk->sk_state != TCP_ESTABLISHED)) {
+	if (unlikely(READ_ONCE(sk->sk_state) != TCP_ESTABLISHED)) {
 		err = -EINVAL;
 		goto out;
 	}
@@ -3009,7 +3008,7 @@ long unix_inq_len(struct sock *sk)
 	struct sk_buff *skb;
 	long amount = 0;
 
-	if (sk->sk_state == TCP_LISTEN)
+	if (READ_ONCE(sk->sk_state) == TCP_LISTEN)
 		return -EINVAL;
 
 	spin_lock(&sk->sk_receive_queue.lock);
@@ -3121,12 +3120,14 @@ static int unix_compat_ioctl(struct socket *sock, unsigned int cmd, unsigned lon
 static __poll_t unix_poll(struct file *file, struct socket *sock, poll_table *wait)
 {
 	struct sock *sk = sock->sk;
+	unsigned char state;
 	__poll_t mask;
 	u8 shutdown;
 
 	sock_poll_wait(file, sock, wait);
 	mask = 0;
 	shutdown = READ_ONCE(sk->sk_shutdown);
+	state = READ_ONCE(sk->sk_state);
 
 	/* exceptional events? */
 	if (READ_ONCE(sk->sk_err))
@@ -3148,14 +3149,14 @@ static __poll_t unix_poll(struct file *file, struct socket *sock, poll_table *wa
 
 	/* Connection-based need to check for termination and startup */
 	if ((sk->sk_type == SOCK_STREAM || sk->sk_type == SOCK_SEQPACKET) &&
-	    sk->sk_state == TCP_CLOSE)
+	    state == TCP_CLOSE)
 		mask |= EPOLLHUP;
 
 	/*
 	 * we set writable also when the other side has shut down the
 	 * connection. This prevents stuck sockets.
 	 */
-	if (unix_writable(sk))
+	if (unix_writable(sk, state))
 		mask |= EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND;
 
 	return mask;
@@ -3166,12 +3167,14 @@ static __poll_t unix_dgram_poll(struct file *file, struct socket *sock,
 {
 	struct sock *sk = sock->sk, *other;
 	unsigned int writable;
+	unsigned char state;
 	__poll_t mask;
 	u8 shutdown;
 
 	sock_poll_wait(file, sock, wait);
 	mask = 0;
 	shutdown = READ_ONCE(sk->sk_shutdown);
+	state = READ_ONCE(sk->sk_state);
 
 	/* exceptional events? */
 	if (READ_ONCE(sk->sk_err) ||
@@ -3191,19 +3194,14 @@ static __poll_t unix_dgram_poll(struct file *file, struct socket *sock,
 		mask |= EPOLLIN | EPOLLRDNORM;
 
 	/* Connection-based need to check for termination and startup */
-	if (sk->sk_type == SOCK_SEQPACKET) {
-		if (sk->sk_state == TCP_CLOSE)
+	if (sk->sk_type == SOCK_SEQPACKET && state == TCP_CLOSE)
 		mask |= EPOLLHUP;
-		/* connection hasn't started yet? */
-		if (sk->sk_state == TCP_SYN_SENT)
-			return mask;
-	}
 
 	/* No write status requested, avoid expensive OUT tests. */
 	if (!(poll_requested_events(wait) & (EPOLLWRBAND|EPOLLWRNORM|EPOLLOUT)))
 		return mask;
 
-	writable = unix_writable(sk);
+	writable = unix_writable(sk, state);
 	if (writable) {
 		unix_state_lock(sk);
 

net/unix/diag.c

@@ -65,7 +65,7 @@ static int sk_diag_dump_icons(struct sock *sk, struct sk_buff *nlskb)
 	u32 *buf;
 	int i;
 
-	if (sk->sk_state == TCP_LISTEN) {
+	if (READ_ONCE(sk->sk_state) == TCP_LISTEN) {
 		spin_lock(&sk->sk_receive_queue.lock);
 
 		attr = nla_reserve(nlskb, UNIX_DIAG_ICONS,
@@ -103,8 +103,8 @@ static int sk_diag_show_rqlen(struct sock *sk, struct sk_buff *nlskb)
 {
 	struct unix_diag_rqlen rql;
 
-	if (sk->sk_state == TCP_LISTEN) {
-		rql.udiag_rqueue = sk->sk_receive_queue.qlen;
+	if (READ_ONCE(sk->sk_state) == TCP_LISTEN) {
+		rql.udiag_rqueue = skb_queue_len_lockless(&sk->sk_receive_queue);
 		rql.udiag_wqueue = sk->sk_max_ack_backlog;
 	} else {
 		rql.udiag_rqueue = (u32) unix_inq_len(sk);
@@ -136,7 +136,7 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 	rep = nlmsg_data(nlh);
 	rep->udiag_family = AF_UNIX;
 	rep->udiag_type = sk->sk_type;
-	rep->udiag_state = sk->sk_state;
+	rep->udiag_state = READ_ONCE(sk->sk_state);
 	rep->pad = 0;
 	rep->udiag_ino = sk_ino;
 	sock_diag_save_cookie(sk, rep->udiag_cookie);
@@ -165,7 +165,7 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 	    sock_diag_put_meminfo(sk, skb, UNIX_DIAG_MEMINFO))
 		goto out_nlmsg_trim;
 
-	if (nla_put_u8(skb, UNIX_DIAG_SHUTDOWN, sk->sk_shutdown))
+	if (nla_put_u8(skb, UNIX_DIAG_SHUTDOWN, READ_ONCE(sk->sk_shutdown)))
 		goto out_nlmsg_trim;
 
 	if ((req->udiag_show & UDIAG_SHOW_UID) &&
@@ -215,7 +215,7 @@ static int unix_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
 		sk_for_each(sk, &net->unx.table.buckets[slot]) {
 			if (num < s_num)
 				goto next;
-			if (!(req->udiag_states & (1 << sk->sk_state)))
+			if (!(req->udiag_states & (1 << READ_ONCE(sk->sk_state))))
 				goto next;
 			if (sk_diag_dump(sk, skb, req, sk_user_ns(skb->sk),
 					 NETLINK_CB(cb->skb).portid,