tcp: Fix a data-race around sysctl_tcp_notsent_lowat.

[ Upstream commit 55be873695ed8912eb77ff46d1d1cadf028bd0f3 ]

While reading sysctl_tcp_notsent_lowat, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: c9bee3b7fdec ("tcp: TCP_NOTSENT_LOWAT socket option")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index da75513a77d455673cd78beb15cc79b1ad6d1d36..aa46f4016245861898d8ec4a5ec0b9e6d57d8da5 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1973,7 +1973,7 @@ 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 ?: net->ipv4.sysctl_tcp_notsent_lowat;
+       return tp->notsent_lowat ?: READ_ONCE(net->ipv4.sysctl_tcp_notsent_lowat);
 }
 
 /* @wake is one when sk_stream_write_space() calls us.