linux-kernel - Re: [PATCH] proc: reject "." and ".." as filenames

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Date:   Sun, 11 Mar 2018 22:41:53 +0100
From:   Pavel Machek <pavel@....cz>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        eric.dumazet@...il.com, xiyou.wangcong@...il.com, fw@...len.de
Subject: Re: [PATCH] proc: reject "." and ".." as filenames

On Mon 2018-03-12 00:35:34, Alexey Dobriyan wrote:
> On Sun, Mar 11, 2018 at 10:30:58PM +0100, Pavel Machek wrote:
> > On Sat 2018-03-10 03:12:23, Alexey Dobriyan wrote:
> > > Various subsystems can create files and directories in /proc
> > > with names directly controlled by userspace.
> > > 
> > > Which means "/", "." and ".." are no-no.
> > > 
> > > "/" split is already taken care of, do the other 2 prohibited names.
> > 
> > Hmm, patch is probably good idea, but now it means that userspace can
> > trigger WARN()s, and can hide objects from root by naming them '.' and
> > '..'... which is not good.
> 
> Patch rejects creation of such entries.
> 
> And they should be harmless as VFS lookup won't find them, only readdir
> would. It not clear how they could be useful.

Yeah, as I said, that's half of problem.

If I can name my object "." and it will be hidden from root, that
sounds like a security hole to be prevented.

So if you know _which_ subsystem allow creating files and directories
in /proc with names directly controlled by userspace, please let us
know, we want to fix that.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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