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From: Kees Cook <keescook@chromium.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: ariadne@dereferenced.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, ebiederm@xmission.com,
	viro@zeniv.linux.org.uk
Subject: Re: [PATCH] fs/exec: require argv[0] presence in do_execveat_common()
Date: Wed, 26 Jan 2022 16:00:01 -0800	[thread overview]
Message-ID: <202201261558.DAA974162@keescook> (raw)
In-Reply-To: <YfFigbwhImLQqQsQ@localhost.localdomain>

On Wed, Jan 26, 2022 at 06:02:25PM +0300, Alexey Dobriyan wrote:
> >	execve("...", NULL, NULL);
> 
> I personally wrote a program which relies on execve(NULL) to succeed.
> It wasn't an exploit, it was test program against IMA-like kernel
> "only whitelisted executables can run" feature.
> 
> Test copies and "corrupts" itself by appending \0 to the end, then tries
> to reexec itself with execve("/proc/self/exe", NULL, NULL);
> main() if run with argc==0 exits with specific error code.
> 
> Appending \0 breaks checksum so working kernel protection scheme must
> not allow it, therefore if execve(NULL) succeeded, than the parent
> process doing test hard fails.
> 
> Also appending \0 doesn't break ELF structure. In other words,
> if executable A is working (and it is working because it is running)
> then A||\0 is valid executable as well and will run too.
> 
> This is independent from filesystem layout, libc, kernel, dynamic
> libraries, compile options and what not.
> 
> Now QNX doesn't allow execve(NULL) and I don't remember if I changed it
> to the next simplest variant and I don't work anymore at that company,
> so I can't check :^)
> 
> 	execve("/proc/self/exe", (char*[]){"Alexey", NULL}, NULL);

One of the various suggestions was to inject { path, NULL } when argc=0.

Given that execve(path, NULL, ...) is being used at least a little,
hopefully there is nothing that depends on argc==0... :P

-- 
Kees Cook

  reply	other threads:[~2022-01-27  0:00 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-26 15:02 Alexey Dobriyan
2022-01-27  0:00 ` Kees Cook [this message]
  -- strict thread matches above, loose matches on Subject: below --
2022-01-26  4:39 Ariadne Conill
2022-01-26  6:42 ` Kees Cook
2022-01-26  7:28   ` Kees Cook
2022-01-26 11:18     ` Ariadne Conill
2022-01-26 12:33       ` Heikki Kallasjoki
2022-01-26 23:57         ` Kees Cook
2022-01-27  0:20           ` Eric W. Biederman
2022-01-26 16:59     ` David Laight
2022-01-26 13:27 ` Rich Felker
2022-01-26 14:46   ` Christian Brauner
2022-01-26 17:37   ` Ariadne Conill
2022-02-01 20:54   ` hypervis0r

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