From: Ariadne Conill <ariadne@dereferenced.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Ariadne Conill <ariadne@dereferenced.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Kees Cook <keescook@chromium.org>,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v2] fs/exec: require argv[0] presence in do_execveat_common()
Date: Wed, 26 Jan 2022 12:38:50 -0600 (CST) [thread overview]
Message-ID: <cd808fc1-ec7a-31d-217e-fbc55f7912a3@dereferenced.org> (raw)
In-Reply-To: <YfGNBz0gigWwNnHn@casper.infradead.org>
Hi,
On Wed, 26 Jan 2022, Matthew Wilcox wrote:
> On Wed, Jan 26, 2022 at 10:57:29AM -0600, Eric W. Biederman wrote:
>> Matthew Wilcox <willy@infradead.org> writes:
>>
>>> 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.
>>
>> Where do we reopen fds 0,1,2 for suid execs? I feel silly but I looked
>> through the code fs/exec.c quickly and I could not see it.
>
> I'm wondering if I misremembered and it's being done in ld.so
> rather than in the kernel? That might be the right place to put
> this fix too.
>
>> I am attracted to the notion of converting an empty argv array passed
>> to the kernel into something we can safely pass to userspace.
>>
>> I think it would need to be having the first entry point to "" instead
>> of the first entry being NULL. That would maintain the invariant that you
>> can always dereference a pointer in the argv array.
>
> Yes, I like that better than NULL.
If we are doing {"", NULL}, then I think it makes sense that we could just
say argc == 1 at that point, which probably sidesteps the concern Jann
raised with the {NULL, NULL} patch, no?
Ariadne
next prev parent reply other threads:[~2022-01-26 18:39 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 11:44 [PATCH v2] fs/exec: require argv[0] presence in do_execveat_common() Ariadne Conill
2022-01-26 14:40 ` Matthew Wilcox
2022-01-26 17:41 ` Ariadne Conill
2022-01-26 14:59 ` Matthew Wilcox
2022-01-26 16:40 ` Kees Cook
2022-01-26 16:57 ` Eric W. Biederman
2022-01-26 17:32 ` Ariadne Conill
2022-01-26 18:03 ` Matthew Wilcox
2022-01-26 18:38 ` Ariadne Conill [this message]
2022-01-26 20:09 ` Kees Cook
2022-01-26 20:23 ` Ariadne Conill
2022-01-26 20:56 ` Kees Cook
2022-01-26 21:13 ` Ariadne Conill
2022-01-26 21:25 ` Kees Cook
2022-01-26 21:30 ` Ariadne Conill
2022-01-26 22:49 ` Kees Cook
2022-01-26 23:07 ` Ariadne Conill
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