linux-kernel - Re: [REVIEW][PATCH 1/4] vfs: Don't allow overwriting mounts in the current mount namespace

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Date:	Thu, 21 Nov 2013 12:58:44 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	Andy Lutomirski <luto@...capital.net>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rob Landley <rob@...dley.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthias Schniedermeyer <ms@...d.de>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [REVIEW][PATCH 1/4] vfs: Don't allow overwriting mounts in the current mount namespace

Christoph Hellwig <hch@...radead.org> writes:

> On Fri, Nov 08, 2013 at 02:17:31PM -0800, Eric W. Biederman wrote:
>> > Read what you've written a few lines above.  The part about target->i_mutex
>> > being held.
>> 
>> That works for the rename as unlink case but we don't hold
>> old_dentry->d_inode->i_mutex which is what is needed to prevent a mount
>> on the dentry we are renaming.
>
> It will be held in 3.13.

Only for files, not for directories.  And none of those locks turns out
to be good enough today to prevent the races between mount and rename.
With the result that when mount returns your mount point could be
located just about anywhere, and that is just considering renames of the
actual mountpoint itself.

Eric
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