linux-kernel - Re: [PATCH 0/2] vfs: ensure that dentries are revalidated on open (try #2)

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Message-ID: <20091118072916.720471b0@tlielax.poochiereds.net>
Date:	Wed, 18 Nov 2009 07:29:16 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, ebiederm@...ssion.com,
	adobriyan@...il.com, viro@...IV.linux.org.uk, jamie@...reable.org
Subject: Re: [PATCH 0/2] vfs: ensure that dentries are revalidated on open
 (try #2)

On Wed, 18 Nov 2009 05:19:06 +0100
Pavel Machek <pavel@....cz> wrote:

> Hi!
> 
> > This is the second attempt to fix this problem. The first one attempted
> > to fix this in procfs, but Eric Biederman pointed out that file bind
> > mounts have a similar problem. This set attempts to fix the issue at a
> > higher level, in the generic VFS layer.
> > 
> > In certain situations, when it knows that they are valid, the path
> > walking code will skip revalidating dentries that it finds in the cache.
> > This causes problems with filesystems such as NFSv4 and CIFS that depend
> > on the d_revalidate routine to do opens during lookup.
> 
> ...and it allows bypassing directory permissions. Could we fix both
> here?
> 									Pavel

Does it? Here's what I just did to check that:

# cp /bin/sleep /root/sleep

# ls -l /root /root/sleep
dr-xr-x---. 19 root root  4096 2009-11-18 07:20 /root
-rwxr-xr-x.  1 root root 29152 2009-11-18 07:20 /root/sleep

# /root/sleep 600

...then as unprivileged user:

$ ps -ef | grep sleep 
(find pid of sleep program that root is running)

$ /proc/5258/exe 600
bash: /proc/5258/exe: Permission denied

...it looks like directory permissions are respected here. Did I
misunderstand what you're concerned about?

-- 
Jeff Layton <jlayton@...hat.com>
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