Commit 381a7032 authored May 27, 2023 by Cambda Zhu Committed by Greg Kroah-Hartman Jun 09, 2023

tcp: Return user_mss for TCP_MAXSEG in CLOSE/LISTEN state if user_mss set



[ 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: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: Jack Yang <mingliang@linux.alibaba.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/CANn89i+3kL9pYtkxkwxwNMzvC_w3LNUum_2=3u+UyLBmGmifHA@mail.gmail.com/#t


Signed-off-by: Cambda Zhu <cambda@linux.alibaba.com>
Link: https://lore.kernel.org/netdev/14D45862-36EA-4076-974C-EA67513C92F6@linux.alibaba.com/


Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230527040317.68247-1-cambda@linux.alibaba.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 32e9a9ee

net/ipv4/tcp.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -3451,7 +3451,8 @@ static 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;