linux-kernel - Re: [PATCH v2] fs/exec: require argv[0] presence in do_execveat

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Message-ID: <202201261323.9499FA51@keescook>
Date:   Wed, 26 Jan 2022 13:25:27 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Ariadne Conill <ariadne@...eferenced.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2] fs/exec: require argv[0] presence in
 do_execveat_common()

On Wed, Jan 26, 2022 at 03:13:10PM -0600, Ariadne Conill wrote:
> Looks good to me, but I wonder if we shouldn't set an argv of
> {bprm->filename, NULL} instead of {"", NULL}.  Discussion in IRC led to the
> realization that multicall programs will try to use argv[0] and might crash
> in this scenario.  If we're going to fake an argv, I guess we should try to
> do it right.

They're crashing currently, though, yes? I think the goal is to move
toward making execve(..., NULL, NULL) just not work at all. Using the
{"", NULL} injection just gets us closer to protecting a bad userspace
program. I think things _should_ crash if they try to start depending
on this work-around.

-- 
Kees Cook