linux-ext4 - Re: [PATCH] fs/ext{3,4}: fix potential race when setversion ioctl updates inode

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Date:	Thu, 5 Jan 2012 00:32:54 +0100
From:	Jan Kara <jack@...e.cz>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
Cc:	Djalal Harouni <tixxdz@...ndz.org>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Darrick J. Wong" <djwong@...ibm.com>,
	Theodore Ts'o <tytso@....edu>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	ext4 development <linux-ext4@...r.kernel.org>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] fs/ext{3,4}: fix potential race when setversion ioctl
 updates inode

On Wed 04-01-12 16:15:04, Andreas Dilger wrote:
> On 2012-01-04, at 10:46 AM, Jan Kara wrote:
> > On Tue 03-01-12 02:31:52, Djalal Harouni wrote:
> >> 
> >> The EXT{3,4}_IOC_SETVERSION ioctl() updates the inode without i_mutex,
> >> this can lead to a race with the other operations that update the same
> >> inode.
> >> 
> >> Patch tested.
> > 
> >  OK, so I've taken the patch into my tree, just updated the changelog
> > which result of our discussion in this thread. I also took the ext4 part
> > since there is no risk of conflict and the patch looks obvious.
> 
> Actually, I'd like to hear more about whether this is a real problem, or
> if it is just a theoretical problem found during code inspection or from
> some static code analysis tool?
  As far as I understood that was just a theoretical issue and I applied
the patch just on the grounds that it is more consistent to use i_mutex for
i_generation changes.

> With the metadata checksum feature we were discussing using the inode
> generation as part of the seed for the directory leaf block checksum, so
> that it wasn't possible to incorrectly access stale directory blocks from
> a previous incarnation of the same inode number.
> 
> We were discussing just disabling this ioctl on filesystems with metadata
> checksums, and printing a deprecation warning for filesystems without that
> feature enabled.  I'm not aware of any real-world use for this ioctl, since
> NFS cannot use it to reconstruct handles because there's no API to allocate
> an inode with a specific number, so setting the generation is pointless.
  OK, I didn't know this. I'm fine with deprecating the ioctl if it's
useless but since that's going to take a while I think the cleanup still
makes some sense.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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