From: "Eric W. Biederman" <ebiederm@xmission.com>
To: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>,
Jann Horn <jannh@google.com>,
Ariadne Conill <ariadne@dereferenced.org>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Christian Brauner <brauner@kernel.org>,
Rich Felker <dalias@libc.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, stable@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] fs/binfmt_elf: Add padding NULL when argc == 0
Date: Wed, 26 Jan 2022 14:31:16 -0600 [thread overview]
Message-ID: <87ilu6utm3.fsf@email.froward.int.ebiederm.org> (raw)
In-Reply-To: <202201261210.E0E7EB83@keescook> (Kees Cook's message of "Wed, 26 Jan 2022 12:13:16 -0800")
Kees Cook <keescook@chromium.org> writes:
> On Wed, Jan 26, 2022 at 08:08:14PM +0000, Matthew Wilcox wrote:
>> On Wed, Jan 26, 2022 at 11:58:39AM -0800, Kees Cook wrote:
>> > We can't mutate argc; it'll turn at least some userspace into an
>> > infinite loop:
>> > https://sources.debian.org/src/valgrind/1:3.18.1-1/none/tests/execve.c/?hl=22#L22
>>
>> How does that become an infinite loop? We obviously wouldn't mutate
>> argc in the caller, just the callee.
>
> Oh, sorry, I misread. It's using /bin/true, not argv[0] (another bit of
> code I found was using argv[0]). Yeah, {"", NULL} could work.
>
>> Also, there's a version of this where we only mutate argc if we're
>> executing a setuid program, which would remove the privilege
>> escalation part of things.
>
> True; though I'd like to keep the logic as non-specialized as possible.
> I don't like making stuff conditional on privilege boundaries if we can
> make it always happen.
Which I think means turning the argc == 0 case into { "", NULL }.
I think we can always do that, and it is already valid in userspace.
The only case I can imagine breaking would be an explicitly testing
for argc == 0 and behaving completely differently if that is passed
to the program.
Eric
next prev parent reply other threads:[~2022-01-26 20:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 17:57 [PATCH] fs/binfmt_elf: Add padding NULL when argc == 0 Kees Cook
2022-01-26 18:07 ` Jann Horn
2022-01-26 18:42 ` Ariadne Conill
2022-01-26 19:50 ` Jann Horn
2022-01-26 19:58 ` Kees Cook
2022-01-26 20:08 ` Matthew Wilcox
2022-01-26 20:13 ` Kees Cook
2022-01-26 20:31 ` Eric W. Biederman [this message]
2022-01-26 19:56 ` Kees Cook
2022-01-26 20:10 ` Ariadne Conill
2022-01-26 20:46 ` Ariadne Conill
2022-01-26 20:52 ` Rich Felker
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