dax: fix dax_range_compare_iter() to use correct size and address offset

dax_range_compare_iter() has two bugs in how it calls
dax_iomap_direct_access() and uses the returned addresses:

1. The size argument passed to dax_iomap_direct_access() is
   ALIGN(pos + len, PAGE_SIZE), which is an absolute file offset
   rather than a length. This causes the underlying dax_direct_access()
   to request a massively inflated nr_pages via PHYS_PFN(size).

2. The addresses returned by dax_iomap_direct_access() are page-aligned
   starting addresses, but memcmp() compares from saddr/daddr directly
   without adding the page-in-page offset of pos1/pos2. When pos1/pos2
   are not page-aligned, this compares the wrong data.

Fix the size by computing ALIGN(len + offset_in_page(pos), PAGE_SIZE),
matching the pattern used in dax_iomap_copy_around(). Fix the address
by adding offset_in_page(pos1)/offset_in_page(pos2) to saddr/daddr in
the memcmp() call.

Fixes: 6f7db3894ae2 ("fsdax: dedup file range to use a compare function")
Cc: stable@vger.kernel.org
Signed-off-by: Jianyun Gao <jianyungao89@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20261011064840.1296-1-jianyungao89@gmail.com
Signed-off-by: Alison Schofield <alison.schofield@intel.com>

0 files changed, 0 insertions, 0 deletions