Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 26 Jan 2022 13:25:27 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Ariadne Conill <ariadne@dereferenced.org>
Cc:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Eric Biederman <ebiederm@xmission.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v2] fs/exec: require argv[0] presence in
 do_execveat_common()
Message-ID: <202201261323.9499FA51@keescook>
References: <20220126114447.25776-1-ariadne@dereferenced.org>
 <202201261202.EC027EB@keescook>
 <a8fef39-27bf-b25f-7cfe-21782a8d3132@dereferenced.org>
 <202201261239.CB5D7C991A@keescook>
 <5e963fab-88d4-2039-1cf4-6661e9bd16b@dereferenced.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5e963fab-88d4-2039-1cf4-6661e9bd16b@dereferenced.org>
Precedence: bulk

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