Patch "tcp: annotate data-races around tp->notsent_lowat" 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

    tcp: annotate data-races around tp->notsent_lowat

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:
     tcp-annotate-data-races-around-tp-notsent_lowat.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 3537464fefdcffe80ddaabe1713aab6c192844dd
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Wed Jul 19 21:28:55 2023 +0000

    tcp: annotate data-races around tp->notsent_lowat
    
    [ Upstream commit 1aeb87bc1440c5447a7fa2d6e3c2cca52cbd206b ]
    
    tp->notsent_lowat can be read locklessly from do_tcp_getsockopt()
    and tcp_poll().
    
    Fixes: c9bee3b7fdec ("tcp: TCP_NOTSENT_LOWAT socket option")
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230719212857.3943972-10-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2f456bed33ec3..4e909148fce39 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1953,7 +1953,11 @@ void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
 {
 	struct net *net = sock_net((struct sock *)tp);
-	return tp->notsent_lowat ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat);
+	u32 val;
+
+	val = READ_ONCE(tp->notsent_lowat);
+
+	return val ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat);
 }
 
 /* @wake is one when sk_stream_write_space() calls us.
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index eb70c1b866d0f..c980d18d99094 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3165,7 +3165,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 		err = tcp_repair_set_window(tp, optval, optlen);
 		break;
 	case TCP_NOTSENT_LOWAT:
-		tp->notsent_lowat = val;
+		WRITE_ONCE(tp->notsent_lowat, val);
 		sk->sk_write_space(sk);
 		break;
 	case TCP_INQ:
@@ -3642,7 +3642,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 		val = tcp_time_stamp_raw() + tp->tsoffset;
 		break;
 	case TCP_NOTSENT_LOWAT:
-		val = tp->notsent_lowat;
+		val = READ_ONCE(tp->notsent_lowat);
 		break;
 	case TCP_INQ:
 		val = tp->recvmsg_inq;