linux-kernel - Re: [patch] unprivileged mounts update

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Message-ID: <462F87EA.1000002@zytor.com>
Date:	Wed, 25 Apr 2007 09:55:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	akpm@...ux-foundation.org, serue@...ibm.com, viro@....linux.org.uk,
	linuxram@...ibm.com, ebiederm@...ssion.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org
Subject: Re: [patch] unprivileged mounts update

Miklos Szeredi wrote:
> 
> Andrew, please skip this patch, for now.
> 
> Serge found a problem with the fsuid approach: setfsuid(nonzero) will
> remove filesystem related capabilities.  So even if root is trying to
> set the "user=UID" flag on a mount, access to the target (and in case
> of bind, the source) is checked with user privileges.
> 
> Root should be able to set this flag on any mountpoint, _regardless_
> of permissions.
> 

Right, if you're using fsuid != 0, you're not running as root (fsuid is
the equivalent to euid for the filesystem.)

I fail to see how ruid should have *any* impact on mount(2).  That seems
to be a design flaw.

	-hpa
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