[PATCH] xfs: Add readpage() check up for mmap file at xfs_file_mmap()

[PATCH] xfs: Add readpage() check up for mmap file at xfs_file_mmap()

[Jeff Liu]

Hello,

When studying XFS code, I found xfs_file_mmap() does not check whether a specific file has readpage() or not.
Actually, I have no idea of which kind of file does not supply page reading function, but Btrfs/Ext4
as well as generic_file_mmap() all do this check at first, do we also need a defense here?

Thanks,
-Jeff


Signed-off-by: Jie Liu <jeff.liu@oracle.com>

---
 fs/xfs/xfs_file.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 9f7ec15..92ad4a5 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -945,6 +945,11 @@ xfs_file_mmap(
 	struct file	*filp,
 	struct vm_area_struct *vma)
 {
+	struct address_space *mapping = file->f_mapping;
+
+	if (!mapping->a_ops->readpage)
+		return -ENOEXEC;
+
 	vma->vm_ops = &xfs_file_vm_ops;
 	vma->vm_flags |= VM_CAN_NONLINEAR;
 
-- 
1.7.9

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Re: [PATCH] xfs: Add readpage() check up for mmap file at xfs_file_mmap()

[Christoph Hellwig]

On Wed, Jul 18, 2012 at 10:47:28PM +0800, Jeff Liu wrote:
> Hello,
> 
> When studying XFS code, I found xfs_file_mmap() does not check whether a specific file has readpage() or not.
> Actually, I have no idea of which kind of file does not supply page reading function, but Btrfs/Ext4
> as well as generic_file_mmap() all do this check at first, do we also need a defense here?

It's not needed. In generic_file_mmap it might make a little sense as
any filesystem could use it, but even there's it's questionable because
->readpage is the only way to actually supposed mmap when using
generic_file_mmap.

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Re: [PATCH] xfs: Add readpage() check up for mmap file at xfs_file_mmap()

[Jeff Liu]

On 07/18/2012 11:11 PM, Christoph Hellwig wrote:

> On Wed, Jul 18, 2012 at 10:47:28PM +0800, Jeff Liu wrote:
>> Hello,
>>
>> When studying XFS code, I found xfs_file_mmap() does not check whether a specific file has readpage() or not.
>> Actually, I have no idea of which kind of file does not supply page reading function, but Btrfs/Ext4
>> as well as generic_file_mmap() all do this check at first, do we also need a defense here?
> 
> It's not needed. In generic_file_mmap it might make a little sense as
> any filesystem could use it, but even there's it's questionable because
> ->readpage is the only way to actually supposed mmap when using
> generic_file_mmap.

Now I got it, thanks for the teaching.

Thanks,
-Jeff

> 
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs


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