[PATCH 5.10 502/509] tcp: annotate data-races around tp->notsent_lowat

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From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ 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>
---
 include/net/tcp.h | 6 +++++-
 net/ipv4/tcp.c    | 4 ++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index be81a930b91fa..dcca41f3a2240 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1991,7 +1991,11 @@ 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 50d674d35e520..8a441dfd258d5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3437,7 +3437,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		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:
@@ -3913,7 +3913,7 @@ 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;
-- 
2.39.2






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