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

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Date:   Wed, 26 Jan 2022 14:59:52 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Ariadne Conill <ariadne@...eferenced.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        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 11:44:47AM +0000, Ariadne Conill wrote:
> Interestingly, Michael Kerrisk opened an issue about this in 2008[1],
> but there was no consensus to support fixing this issue then.
> Hopefully now that CVE-2021-4034 shows practical exploitative use
> of this bug in a shellcode, we can reconsider.
> 
> [0]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=8408

Having now read 8408 ... if ABI change is a concern (and I really doubt
it is), we could treat calling execve() with a NULL argv as if the
caller had passed an array of length 1 with the first element set to
NULL.  Just like we reopen fds 0,1,2 for suid execs if they were closed.