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From: Alexey Dobriyan <adobriyan@gmail.com>
To: ariadne@dereferenced.org, keescook@chromium.org
Cc: 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 18:02:25 +0300	[thread overview]
Message-ID: <YfFigbwhImLQqQsQ@localhost.localdomain> (raw)

>	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);

P.S.:

	> tptacek 5 minutes ago | root | parent | next [–]
	> There is not.

	Yes, there is!

             reply	other threads:[~2022-01-26 15:02 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-26 15:02 Alexey Dobriyan [this message]
2022-01-27  0:00 ` Kees Cook
  -- 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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