[PATCH 5.15 065/201] tcp: Fix data-races around sysctl_tcp_min_snd_mss.

Greg Kroah-Hartman
2022-07-27T17:07:10Z

From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit 78eb166cdefcc3221c8c7c1e2d514e91a2eb5014 ]

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

Fixes: 5f3e2bf008c2 ("tcp: add tcp_min_snd_mss sysctl")
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/tcp_output.c | 3 ++-
net/ipv4/tcp_timer.c | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 53277a9a2300..b4a8a5b9350f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1722,7 +1722,8 @@ static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
mss_now -= icsk->icsk_ext_hdr_len;

/* Then reserve room for full set of TCP options and 8 bytes of data */
- mss_now = max(mss_now, sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss);
+ mss_now = max(mss_now,
+ READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss));
return mss_now;
}

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 04063c7e33ba..39107bb730b0 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -173,7 +173,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
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);
+ mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_min_snd_mss));
icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
}
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
--
2.35.1