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Date: Sat, 15 Dec 2012 18:12:11 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: linux-kernel@vger.kernel.org
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: oopsable race in xen-gntdev (unsafe vma access)
Message-ID: <20121215181211.GV4939@ZenIV.linux.org.uk>
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	1) find_vma() is *not* safe without ->mmap_sem and its result may
very well be freed just as it's returned to caller.  IOW,
gntdev_ioctl_get_offset_for_vaddr() is racy and may end up with
dereferencing freed memory.

	2) gntdev_vma_close() is putting NULL into map->vma with only
->mmap_sem held by caller.  Things like
                if (!map->vma)
                        continue;
                if (map->vma->vm_start >= end)
                        continue;
                if (map->vma->vm_end <= start)
done with just priv->lock held are racy.

	I'm not familiar with the code, but it looks like we need to
protect gntdev_vma_close() guts with the same spinlock and probably
hold ->mmap_sem shared around the "find_vma()+get to map->{index,count}"
in the ioctl.  Or replace the logics in ioctl with search through the
list of grant_map under the same spinlock...

	Comments?