From: Cambda Zhu <cambda@xxxxxxxxxxxxxxxxx>
[ Upstream commit 34dfde4ad87b84d21278a7e19d92b5b2c68e6c4d ]
This patch replaces the tp->mss_cache check in getting TCP_MAXSEG
with tp->rx_opt.user_mss check for CLOSE/LISTEN sock. Since
tp->mss_cache is initialized with TCP_MSS_DEFAULT, checking if
it's zero is probably a bug.
With this change, getting TCP_MAXSEG before connecting will return
default MSS normally, and return user_mss if user_mss is set.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Jack Yang <mingliang@xxxxxxxxxxxxxxxxx>
Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/netdev/CANn89i+3kL9pYtkxkwxwNMzvC_w3LNUum_2=3u+UyLBmGmifHA@xxxxxxxxxxxxxx/#t
Signed-off-by: Cambda Zhu <cambda@xxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/netdev/14D45862-36EA-4076-974C-EA67513C92F6@xxxxxxxxxxxxxxxxx/
Reviewed-by: Jason Xing <kerneljasonxing@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230527040317.68247-1-cambda@xxxxxxxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/ipv4/tcp.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f4b243cc7f4a5..6bb8eb8031051 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4077,7 +4077,8 @@ int do_tcp_getsockopt(struct sock *sk, int level,
switch (optname) {
case TCP_MAXSEG:
val = tp->mss_cache;
- if (!val && ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
+ if (tp->rx_opt.user_mss &&
+ ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
val = tp->rx_opt.user_mss;
if (tp->repair)
val = tp->rx_opt.mss_clamp;
--
2.39.2
