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Date: Mon, 3 Aug 2009 17:49:30 -0400
From: Christoph Hellwig <hch@infradead.org>
To: Ramon de Carvalho Valle <ramon@risesecurity.org>
Cc: linux-kernel@vger.kernel.org, mszeredi@novell.com, hch@lst.de,
       xfs@oss.sgi.com
Subject: Re: [PATCH 1/1] XFS: __xfs_get_blocks check pointer to the target
	device
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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.