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

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Date:	Wed, 4 Jan 2012 00:14:32 +0100
From:	Djalal Harouni <tixxdz@...ndz.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Theodore Ts'o <tytso@....edu>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	linux-ext4@...r.kernel.org, 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 Tue, Jan 03, 2012 at 01:46:24PM +0100, Jan Kara wrote:
>   Hello,
> 
> 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.
>   Thanks for the patch but I don't quite understand the problem.
> i_generation is set when:
>   a) inode is loaded from disk
>   b) inode is allocated
>   c) in SETVERSION ioctl
> 
>   The only thing that can race here seems to be c) against c) and that is
> racy with i_mutex as well. So what problems do you exactly observe without
> the patch?
Right, but what about the related i_ctime change ? (i_ctime is updated in
other places...)

The i_ctime update must reflect the _appropriate_ inode modification
operation. This is why IMHO we should protect them to avoid a lost update.

BTW the i_generation which is used by NFS and fuse filesystems is updated
even if the inode is marked immutable, is this the intended behaviour?


> 								Honza
Thanks for your response.

-- 
tixxdz
http://opendz.org
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