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

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Message-ID: <64e91dc2-7f5c-6e8-308e-414c82a8ae6b@dereferenced.org>
Date:   Wed, 26 Jan 2022 15:30:13 -0600 (CST)
From:   Ariadne Conill <ariadne@...eferenced.org>
To:     Kees Cook <keescook@...omium.org>
cc:     Ariadne Conill <ariadne@...eferenced.org>,
        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()

Hi,

On Wed, 26 Jan 2022, Kees Cook wrote:

> 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.

Is there a reason to spawn a program, just to have it crash, rather than 
just denying it to begin with, though?

I mean, it all seems fine enough, and perhaps I'm just a bit picky on the 
colors and flavors of my bikesheds, so if you want to go with this patch, 
I'll be glad to carry it in the Alpine security update I am doing to make 
sure the *other* GLib-using SUID programs people find don't get exploited 
in the same way.

Ariadne