linux-kernel - Re: [PATCH] proc: fix races against execve() of /proc/PID/{fd/,fdinfo/,fdinfo/*}

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Date:	Fri, 26 Aug 2011 12:40:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	kernel-hardening@...ts.openwall.com,
	Al Viro <viro@...iv.linux.org.uk>,
	David Rientjes <rientjes@...gle.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, security@...nel.org
Subject: Re: [PATCH] proc: fix races against execve() of
 /proc/PID/{fd/,fdinfo/,fdinfo/*}

On Fri, 26 Aug 2011 17:29:09 +0400
Vasiliy Kulikov <segoon@...nwall.com> wrote:

> fd* files are restricted to the task's owner, and other users may not
> get direct access to them.  But one may open any of these files and run
> any setuid program, keeping opened file descriptors.  As there are
> permission checks on open(), but not on readdir() and read(), operations
> on the kept file descriptors will not be checked.  It makes it possible
> to violate procfs permission model.
> 
> Reading fdinfo/* may disclosure current fds' position and flags, reading
> directory contents of fdinfo/ and fd/ may disclosure the number of opened
> files by the target task.  This information is not sensible per se, but
> it can reveal some private information (like length of a password stored in
> a file) under certain conditions.
> 
> Used existing (un)lock_trace functions to deal with the issue by calling
> ptrace_may_access() permission checks.

This doesn't apply to current mainline.  Please redo, retest, resend?
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