linux-kernel - Re: [PATCH 1/1] XFS: __xfs_get_blocks check pointer to the target device

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Message-ID: <4A786110.8090404@sandeen.net>
Date:	Tue, 04 Aug 2009 11:25:52 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Ramon de Carvalho Valle <ramon@...esecurity.org>
CC:	Christoph Hellwig <hch@...radead.org>, xfs@....sgi.com, hch@....de,
	linux-kernel@...r.kernel.org, mszeredi@...ell.com
Subject: Re: [PATCH 1/1] XFS: __xfs_get_blocks check pointer to the target
 device

Ramon de Carvalho Valle wrote:
> On Mon, 2009-08-03 at 17:49 -0400, Christoph Hellwig wrote:
>> On Mon, Aug 03, 2009 at 05:03:28PM -0300, Ramon de Carvalho Valle wrote:
>>> The __xfs_get_blocks function does not check if the pointer to the target
>>> device is valid before dereferencing it.
>> It should never be zero.  It's set by xfs_imap_to_bmap to either
>> mp->m_ddev_targp which is always allocated, or to mp->m_rtdev_targp
>> which is always allocated if we have a realtime device, and
>> XFS_IS_REALTIME_INODE should only be true in that case.
>>
> 
> While testing XFS code with a modified version of fsfuzzer on SLES 10
> SP3 (Kernel 2.6.16.60-0.49.3.ramon-ppc64), I came across the following
> Oops:

...

ahah, useful information that would have been great in the original
patch submission.  :)

> I added a printk() line just before the:
> 
> 	bh_result->b_bdev = iomap.iomap_target->bt_bdev;
> 
> and as we can see iomap.iomap_target is NULL.
> 
> My guess is that the XFS_DIFLAG_REALTIME flag is being set incorrectly
> on the xfs inode structure, setting iomapp->iomap_target to the wrong
> device pointer (probably NULL).
> 
> I don't know if this is the best place to add a check, neither if
> returning -XFS_ERROR(EIO) is correct at this point. Maybe doing:
> 
> 	if (iomap.iomap_target && omap.iomap_flags & IOMAP_REALTIME)
> 		bh_result->b_bdev = iomap.iomap_target->bt_bdev;
> 
> would be a better solution.

Can you test hch's patch w/ your fuzzed image?

Thanks,
-Eric
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