Patch "net: datagram: fix data-races in datagram_poll()" 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

    net: datagram: fix data-races in datagram_poll()

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:
     net-datagram-fix-data-races-in-datagram_poll.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 021c354160e601e96e1e68abeb3296b30aaa5a52
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Tue May 9 17:31:31 2023 +0000

    net: datagram: fix data-races in datagram_poll()
    
    [ Upstream commit 5bca1d081f44c9443e61841842ce4e9179d327b6 ]
    
    datagram_poll() runs locklessly, we should add READ_ONCE()
    annotations while reading sk->sk_err, sk->sk_shutdown and sk->sk_state.
    
    Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230509173131.3263780-1-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/datagram.c b/net/core/datagram.c
index b0488f30f2c4e..a5fc44448d600 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -778,18 +778,21 @@ __poll_t datagram_poll(struct file *file, struct socket *sock,
 {
 	struct sock *sk = sock->sk;
 	__poll_t mask;
+	u8 shutdown;
 
 	sock_poll_wait(file, sock, wait);
 	mask = 0;
 
 	/* exceptional events? */
-	if (sk->sk_err || !skb_queue_empty_lockless(&sk->sk_error_queue))
+	if (READ_ONCE(sk->sk_err) ||
+	    !skb_queue_empty_lockless(&sk->sk_error_queue))
 		mask |= EPOLLERR |
 			(sock_flag(sk, SOCK_SELECT_ERR_QUEUE) ? EPOLLPRI : 0);
 
-	if (sk->sk_shutdown & RCV_SHUTDOWN)
+	shutdown = READ_ONCE(sk->sk_shutdown);
+	if (shutdown & RCV_SHUTDOWN)
 		mask |= EPOLLRDHUP | EPOLLIN | EPOLLRDNORM;
-	if (sk->sk_shutdown == SHUTDOWN_MASK)
+	if (shutdown == SHUTDOWN_MASK)
 		mask |= EPOLLHUP;
 
 	/* readable? */
@@ -798,10 +801,12 @@ __poll_t datagram_poll(struct file *file, struct socket *sock,
 
 	/* Connection-based need to check for termination and startup */
 	if (connection_based(sk)) {
-		if (sk->sk_state == TCP_CLOSE)
+		int state = READ_ONCE(sk->sk_state);
+
+		if (state == TCP_CLOSE)
 			mask |= EPOLLHUP;
 		/* connection hasn't started yet? */
-		if (sk->sk_state == TCP_SYN_SENT)
+		if (state == TCP_SYN_SENT)
 			return mask;
 	}