linux-kernel - Re: ls -l /proc/1/exe -> Permission denied

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Message-ID: <87k376siuw.fsf@x220.int.ebiederm.org>
Date:	Mon, 21 Jul 2014 10:48:55 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Richard Weinberger <richard@....at>
Cc:	Andreas Schwab <schwab@...ux-m68k.org>,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: ls -l /proc/1/exe -> Permission denied

Richard Weinberger <richard@....at> writes:

> Am 20.07.2014 13:51, schrieb Andreas Schwab:
>> Richard Weinberger <richard.weinberger@...il.com> writes:
>>> Do you have an example?
>> 
>> proc symlinks are special because they actually resolve to the inode.
>
> Ah. If an attacker manages the kernel to follow the symlink he could
> indirectly access that file.
> Thanks for pointing this out!

We only allow this access for processes that we are allowed to ptrace
because knowing intimate details of a process such as which files it has
open and in this case which file it is executing can make it more
attackable. (Say by looking to see if a processes is still running some
old vulnerable version and hasn't been restarted yet).

Normally this only applies to processes owned by different users.

However some configurations restrict ptrace on processes that you own.
You will have to look at the ``security'' modules you have enabled
and configured to see what that policy is, to see why you aren't allowed
to access your own processes.

Eric
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