[PATCH 5.15 064/201] tcp: Fix data-races around sysctl_tcp_base_mss.

[Greg Kroah-Hartman]

From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

[ Upstream commit 88d78bc097cd8ebc6541e93316c9d9bf651b13e8 ]

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

Fixes: 5d424d5a674f ("[TCP]: MTU probing")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/ipv4/tcp_output.c | 2 +-
 net/ipv4/tcp_timer.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 1acfd4298a01..53277a9a2300 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1768,7 +1768,7 @@ void tcp_mtup_init(struct sock *sk)
 	icsk->icsk_mtup.enabled = READ_ONCE(net->ipv4.sysctl_tcp_mtu_probing) > 1;
 	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
 			       icsk->icsk_af_ops->net_header_len;
-	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
+	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, READ_ONCE(net->ipv4.sysctl_tcp_base_mss));
 	icsk->icsk_mtup.probe_size = 0;
 	if (icsk->icsk_mtup.enabled)
 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 98bb00e29e1e..04063c7e33ba 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -171,7 +171,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
 	} else {
 		mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
-		mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
+		mss = min(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss);
 		mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);
 		mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
 		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
-- 
2.35.1