linux-kernel - Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE

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Date:   Wed, 7 Jun 2017 05:40:21 +1000
From:   Aleksa Sarai <asarai@...e.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Roland McGrath <roland@...k.frob.com>,
        linux-api@...r.kernel.org,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD

> Another easy entry point is to see that a multi-threaded setuid won't
> change the credentials on a zombie thread group leader.  Which can allow
> sending signals to a process that the credential change should forbid.
> This is in violation of posix and the semantics we attempt to enforce in
> linux.

I might be completely wrong on this point (and I haven't looked at the 
patches), but I was under the impression that multi-threaded set[ug]id 
was implemented in userspace (by glibc's nptl(7) library that uses RT 
signals internally to get each thread to update their credentials). And 
given that, I wouldn't be surprised (as a user) that zombie threads will 
have stale credentials (glibc isn't running in those threads anymore).

Am I mistaken in that belief?

</off-topic>

-- 
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/