netdev - [Question]about the commit tcp: randomize timestamps on syncookies

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>] [day] [month] [year] [list]

Message-ID: <CAMaK5_g-aZjHSzTd73LsqLRWOXhTpjUGsPsxax5YjCEYHAeO7A@mail.gmail.com>
Date: Thu, 24 Aug 2023 14:39:45 +0800
From: Xin Guo <guoxin0309@...il.com>
To: netdev@...r.kernel.org
Subject: [Question]about the commit tcp: randomize timestamps on syncookies

Hi,
when i read the code about the commit
84b114b98452c431299d99c135f751659e517acb tcp: randomize timestamps on
syncookie, i cannot understand the code
in cookie_v4_check：

tsoff = secure_tcp_ts_off(...)
tcp_opt.rcv_tsecr -= tsoff


in my view, this tsoff is different with that which we used when we send SYNACK,

why rcv_tsecr can directly be subtracted by tsoff? any thought behind it?

any feedback is welcome, thanks.

Regards

Xin.