netdev - Re: [PATCH net] tcp: reduce accepted window in NEW_SYN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Fri, 24 May 2024 16:50:42 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Jason Xing <kernelxing@...cent.com>, Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net] tcp: reduce accepted window in NEW_SYN_RECV state

On Thu, May 23, 2024 at 9:07 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Jason commit made checks against ACK sequence less strict
> and can be exploited by attackers to establish spoofed flows
> with less probes.
>
> Innocent users might use tcp_rmem[1] == 1,000,000,000,
> or something more reasonable.
>
> An attacker can use a regular TCP connection to learn the server
> initial tp->rcv_wnd, and use it to optimize the attack.
>
> If we make sure that only the announced window (smaller than 65535)
> is used for ACK validation, we force an attacker to use
> 65537 packets to complete the 3WHS (assuming server ISN is unknown)
>
> Fixes: 378979e94e95 ("tcp: remove 64 KByte limit for initial tp->rcv_wnd value")
> Link: https://datatracker.ietf.org/meeting/119/materials/slides-119-tcpm-ghost-acks-00
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Jason Xing <kernelxing@...cent.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>

Reviewed-by: Jason Xing <kerneljasonxing@...il.com>

Thank you, Eric!