netdev - Re: [PATCH net v1] tcp: Return user_mss for TCP_MAXSEG in CLOSE/LISTEN state if user

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Date: Wed, 24 May 2023 17:10:54 +0800
From: Cambda Zhu <cambda@...ux.alibaba.com>
To: netdev@...r.kernel.org,
 Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Jason Xing <kerneljasonxing@...il.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Dust Li <dust.li@...ux.alibaba.com>,
 Tony Lu <tonylu@...ux.alibaba.com>,
 Jack Yang <mingliang@...ux.alibaba.com>
Subject: Re: [PATCH net v1] tcp: Return user_mss for TCP_MAXSEG in
 CLOSE/LISTEN state if user_mss set


> On May 24, 2023, at 16:33, Cambda Zhu <cambda@...ux.alibaba.com> wrote:
> 
> 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: 0c409e85f0ac ("Import 2.3.41pre2")
> Reported-by: Jack Yang <mingliang@...ux.alibaba.com>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Link: https://lore.kernel.org/netdev/CANn89i+3kL9pYtkxkwxwNMzvC_w3LNUum_2=3u+UyLBmGmifHA@mail.gmail.com/#t
> Signed-off-by: Cambda Zhu <cambda@...ux.alibaba.com>
> Link: https://lore.kernel.org/netdev/14D45862-36EA-4076-974C-EA67513C92F6@linux.alibaba.com/
> ---
> v1:
> - Return default MSS if user_mss not set for backwards compatibility.
> - Send patch to net instead of net-next, with Fixes tag.
> - Add Eric's tags.
> ---
> 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 4d6392c16b7a..3e01a58724b8 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -4081,7 +4081,8 @@ 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;
> -- 
> 2.16.6

I see netdev/verify_fixes check failed for the commit 0c409e85f0ac ("Import 2.3.41pre2").
The commit is from:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git

Should I remove the Fixes tag?

Thanks!

Cambda