linux-kernel - Re: Re: [PATCH] subsystem: pr??oc filesystem

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Message-ID: <20121216142810.GB4939@ZenIV.linux.org.uk>
Date:	Sun, 16 Dec 2012 14:28:10 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	tux2002@...nt.ru
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] subsystem: pr??oc filesystem

On Sun, Dec 16, 2012 at 04:02:03PM +0400, tux2002@...nt.ru wrote:
> Not, this permissions saved for all users for later, check please.

... and that's why it's bogus.  umask of whoever had done lookup for
/proc/<something> affects everybody else.  For as long as the thing stays
in dcache.  At which point it's up for grabs (in that sense) again.
Do (umask 777; ls -l /proc) with your kernel and watch the results.
Note that you don't need to be root to cause that - anyone can do it.

Realize that dentries and inodes in /proc/<pid>/* are created on demand
whenever somebody does a lookup.  So running ps(1) suddenly makes you
a creator of a bunch of those.  Unless somebody else had done ps(1) (or
ls -l /proc, or...) first.  Basing any security decisions on _that_ is
insane.
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