[PATCH 5.18 121/231] tcp: Fix a data-race around sysctl_tcp_ecn_fallback.

Greg Kroah-Hartman
2022-07-19T13:02:38Z

From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit 12b8d9ca7e678abc48195294494f1815b555d658 ]

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

Fixes: 492135557dc0 ("tcp: add rfc3168, section 6.1.1.1. fallback")
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>
---
net/ipv4/sysctl_net_ipv4.c | 2 ++
net/ipv4/tcp_output.c | 2 +-
2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 11add5214713..ffe0264a51b8 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -689,6 +689,8 @@ static struct ctl_table ipv4_net_table[] = {
.maxlen = sizeof(u8),
.mode = 0644,
.proc_handler = proc_dou8vec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
},
{
.procname = "ip_dynaddr",
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 9eefe7f6370f..34249469e361 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -346,7 +346,7 @@ static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)

static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
{
- if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
+ if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback))
/* tp->ecn_flags are cleared at a later point in time when
* SYN ACK is ultimatively being received.
*/
--
2.35.1