On Thu, Jul 28, 2016 at 11:35:34AM -0700, Darrick J. Wong wrote:

Kirill A. Shutemov reports that the kernel doesn't try to cap dest_count
in any way, and uses the number to allocate kernel memory.  This causes
high order allocation warnings in the kernel log if someone passes in a
big enough value.  We should clamp the allocation at PAGE_SIZE to avoid
stressing the VM.

The two existing users of the dedupe ioctl never send more than 120
requests, so we can safely clamp dest_range at PAGE_SIZE, because with
4k pages we can handle up to 127 dedupe candidates.  Given the max
extent length of 16MB, we can end up doing 2GB of IO which is plenty.

Reported-by: "Kirill A. Shutemov" <redacted>
Signed-off-by: Darrick J. Wong <redacted>

Reviewed-by: Mark Fasheh <redacted>

--
Mark Fasheh