Patch "af_unix: Use unix_recvq_full_lockless() in unix_stream_connect()." has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    af_unix: Use unix_recvq_full_lockless() in unix_stream_connect().

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     af_unix-use-unix_recvq_full_lockless-in-unix_stream_.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 605cba8e2051f009e1aa6429c6c1c35ee7651c55
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Tue Jun 4 09:52:38 2024 -0700

    af_unix: Use unix_recvq_full_lockless() in unix_stream_connect().
    
    [ Upstream commit 45d872f0e65593176d880ec148f41ad7c02e40a7 ]
    
    Once sk->sk_state is changed to TCP_LISTEN, it never changes.
    
    unix_accept() takes advantage of this characteristics; it does not
    hold the listener's unix_state_lock() and only acquires recvq lock
    to pop one skb.
    
    It means unix_state_lock() does not prevent the queue length from
    changing in unix_stream_connect().
    
    Thus, we need to use unix_recvq_full_lockless() to avoid data-race.
    
    Now we remove unix_recvq_full() as no one uses it.
    
    Note that we can remove READ_ONCE() for sk->sk_max_ack_backlog in
    unix_recvq_full_lockless() because of the following reasons:
    
      (1) For SOCK_DGRAM, it is a written-once field in unix_create1()
    
      (2) For SOCK_STREAM and SOCK_SEQPACKET, it is changed under the
          listener's unix_state_lock() in unix_listen(), and we hold
          the lock in unix_stream_connect()
    
    Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ec4c462a87f06..ae6aae983b8cb 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -189,15 +189,9 @@ 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)
@@ -1301,7 +1295,7 @@ 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;