From: Jakub Kicinski <kuba@kernel.org>
To: Ren Wei <enjou1224z@gmail.com>
Cc: netdev@vger.kernel.org, dsahern@kernel.org, idosch@nvidia.com,
davem@davemloft.net, edumazet@google.com, pabeni@redhat.com,
horms@kernel.org, vega@nebusec.ai, edragain@163.com
Subject: Re: [PATCH net 1/1] ipv4: reject RTAX_ADVMSS values below TCP_MIN_MSS
Date: Wed, 5 Aug 2026 17:34:26 -0700 [thread overview]
Message-ID: <20260805173426.32dc3780@kernel.org> (raw)
In-Reply-To: <a2e93ae9003f33bf49b789dbd537f4a6c10f26fa.1784972917.git.edragain@163.com>
On Tue, 28 Jul 2026 13:08:17 +0800 Ren Wei wrote:
> ip_metrics_convert() only caps RTAX_ADVMSS at the upper bound and
> still accepts undersized non-zero values from userspace.
>
> A route installed with "advmss 12" can later reach the passive TCP
> open path. When SYN timestamps are enabled, tcp_openreq_init_rwin()
> subtracts TCPOLEN_TSTAMP_ALIGNED from the route advmss before calling
> tcp_select_initial_window(). This can reduce the effective MSS to
> zero and trigger a divide-by-zero in the rounddown(space, mss) path.
>
> Reject non-zero RTAX_ADVMSS values smaller than TCP_MIN_MSS while
> keeping the existing "0 means use default advmss" behavior intact.
>
> This matches the existing TCP_MIN_MSS based validation used for
> TCP_MAXSEG and fixes the bug at the route metric input point rather
> than adding a redundant guard deeper in the TCP stack.
Could you repost this? maybe we'll get more review attention that way.
next prev parent reply other threads:[~2026-08-06 0:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-28 5:08 [PATCH net 0/1] ipv4: fix divide-by-zero from undersized RTAX_ADVMSS Ren Wei
2026-07-28 5:08 ` [PATCH net 1/1] ipv4: reject RTAX_ADVMSS values below TCP_MIN_MSS Ren Wei
2026-07-30 13:35 ` Ido Schimmel
2026-08-04 22:21 ` Jakub Kicinski
2026-08-06 0:34 ` Jakub Kicinski [this message]
2026-08-06 4:13 ` [PATCH net RESEND " Ren Wei
2026-08-06 14:15 ` Jakub Kicinski
2026-08-06 4:13 ` [PATCH net RESEND 0/1] ipv4: fix divide-by-zero from undersized RTAX_ADVMSS Ren Wei
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