linux-kernel - Re: [RFC][PATCH] exec: Move cred computation under exec_update

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

Message-ID: <87a50gxo0i.fsf@email.froward.int.ebiederm.org>
Date: Thu, 20 Nov 2025 17:50:05 -0600
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Bernd Edlinger <bernd.edlinger@...mail.de>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,  Alexey Dobriyan
 <adobriyan@...il.com>,  Oleg Nesterov <oleg@...hat.com>,  Kees Cook
 <kees@...nel.org>,  Andy Lutomirski <luto@...capital.net>,  Will Drewry
 <wad@...omium.org>,  Christian Brauner <brauner@...nel.org>,  Andrew
 Morton <akpm@...ux-foundation.org>,  Michal Hocko <mhocko@...e.com>,
  Serge Hallyn <serge@...lyn.com>,  James Morris
 <jamorris@...ux.microsoft.com>,  Randy Dunlap <rdunlap@...radead.org>,
  Suren Baghdasaryan <surenb@...gle.com>,  Yafang Shao
 <laoar.shao@...il.com>,  Helge Deller <deller@....de>,  Adrian Reber
 <areber@...hat.com>,  Thomas Gleixner <tglx@...utronix.de>,  Jens Axboe
 <axboe@...nel.dk>,  Alexei Starovoitov <ast@...nel.org>,
  "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
  "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
  linux-kselftest@...r.kernel.org,  linux-mm@...ck.org,
  linux-security-module@...r.kernel.org,  tiozhang
 <tiozhang@...iglobal.com>,  Luis Chamberlain <mcgrof@...nel.org>,  "Paulo
 Alcantara (SUSE)" <pc@...guebit.com>,  Sergey Senozhatsky
 <senozhatsky@...omium.org>,  Frederic Weisbecker <frederic@...nel.org>,
  YueHaibing <yuehaibing@...wei.com>,  Paul Moore <paul@...l-moore.com>,
  Aleksa Sarai <cyphar@...har.com>,  Stefan Roesch <shr@...kernel.io>,
  Chao Yu <chao@...nel.org>,  xu xin <xu.xin16@....com.cn>,  Jeff Layton
 <jlayton@...nel.org>,  Jan Kara <jack@...e.cz>,  David Hildenbrand
 <david@...hat.com>,  Dave Chinner <dchinner@...hat.com>,  Shuah Khan
 <shuah@...nel.org>,  Elena Reshetova <elena.reshetova@...el.com>,  David
 Windsor <dwindsor@...il.com>,  Mateusz Guzik <mjguzik@...il.com>,  Ard
 Biesheuvel <ardb@...nel.org>,  "Joel Fernandes (Google)"
 <joel@...lfernandes.org>,  "Matthew Wilcox (Oracle)"
 <willy@...radead.org>,  Hans Liljestrand <ishkamiel@...il.com>,  Penglei
 Jiang <superman.xpt@...il.com>,  Lorenzo Stoakes
 <lorenzo.stoakes@...cle.com>,  Adrian Ratiu <adrian.ratiu@...labora.com>,
  Ingo Molnar <mingo@...nel.org>,  "Peter Zijlstra (Intel)"
 <peterz@...radead.org>,  Cyrill Gorcunov <gorcunov@...il.com>,  Eric
 Dumazet <edumazet@...gle.com>
Subject: Re: [RFC][PATCH] exec: Move cred computation under exec_update_lock

"Eric W. Biederman" <ebiederm@...ssion.com> writes:

> Instead of computing the new cred before we pass the point of no
> return compute the new cred just before we use it.
>
> This allows the removal of fs_struct->in_exec and cred_guard_mutex.
>
> I am not certain why we wanted to compute the cred for the new
> executable so early.  Perhaps I missed something but I did not see any
> common errors being signaled.   So I don't think we loose anything by
> computing the new cred later.

I should add that the permission checks happen in open_exec,
everything that follows credential wise is just about representing in
struct cred the credentials the new executable will have.

So I am really at a loss why we have had this complicated way of
computing of computed the credentials all of these years full of
time of check to time of use problems.

Eric