[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <Yz+Dln7AAMU+Oj9X@mit.edu>
Date: Thu, 6 Oct 2022 21:40:38 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Kees Cook <keescook@...omium.org>
Cc: Jorge Merlino <jorge.merlino@...onical.com>,
Christian Brauner <brauner@...nel.org>,
Eric Biederman <ebiederm@...ssion.com>,
Jann Horn <jannh@...gle.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org,
John Johansen <john.johansen@...onical.com>,
Paul Moore <paul@...l-moore.com>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Eric Paris <eparis@...isplace.org>,
Richard Haines <richard_c_haines@...nternet.com>,
Casey Schaufler <casey@...aufler-ca.com>,
Xin Long <lucien.xin@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Todd Kjos <tkjos@...gle.com>,
Ondrej Mosnacek <omosnace@...hat.com>,
Prashanth Prahlad <pprahlad@...hat.com>,
Micah Morton <mortonm@...omium.org>,
Fenghua Yu <fenghua.yu@...el.com>,
Andrei Vagin <avagin@...il.com>, linux-kernel@...r.kernel.org,
apparmor@...ts.ubuntu.com, linux-security-module@...r.kernel.org,
selinux@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] Fix race condition when exec'ing setuid files
On Thu, Oct 06, 2022 at 01:20:35PM -0700, Kees Cook wrote:
>
> So the question, then, is "why are they trying to exec while actively
> spawning new threads?" That appears to be the core problem here, and as
> far as I can tell, the kernel has behaved this way for a very long time.
> I don't think the kernel should fix this, either, because it leads to a
> very weird state for userspace, where the thread spawner may suddenly
> die due to the exec happening in another thread. This really looks like
> something userspace needs to handle correctly (i.e. don't try to exec
> while actively spawning threads).
One of the classic failure modes is when a threaded program calls a
library, and that library might try to do a fork/exec (or call
system(3) to run some command. e.g., such as running "lvm create ..."
or to spawn some kind of helper daemon.
There are a number of stack overflow questions about this, and there
are some solutions to _some_ of the problems, such as using
pthread_atfork(), and knowing that you are about to call fork/exec,
and use some out of band mechanism to to make sure no threads get
spawned until the fork/exec is completed --- but if you don't know
that a library is going to do a fork/exec, well, life is tough.
One technique even advocated by a stack overflow article is "avoid
using threads whenver possible". :-/
- Ted
Powered by blists - more mailing lists