From: Cambda Zhu cambda@linux.alibaba.com
[ 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@linux.alibaba.com Suggested-by: Eric Dumazet edumazet@google.com Link: https://lore.kernel.org/netdev/CANn89i+3kL9pYtkxkwxwNMzvC_w3LNUum_2=3u+UyLBm... Signed-off-by: Cambda Zhu cambda@linux.alibaba.com Link: https://lore.kernel.org/netdev/14D45862-36EA-4076-974C-EA67513C92F6@linux.al... 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 --- 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 22218ad71409f..cb96775fc86f6 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3376,7 +3376,8 @@ 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;