fs/ntfs3: fix info-leak on partial LZNT decompress in ni_read_frame()

ni_read_frame() decompresses an LZNT $DATA frame into the vmapped target
pages and then trusts decompress_lznt()'s return value:

  unc_size = decompress_lznt(frame_ondisk, ondisk_size, frame_mem,
                             frame_size);
  if ((ssize_t)unc_size < 0)        err = unc_size;
  else if (!unc_size || unc_size > frame_size)  err = -EINVAL;

decompress_lznt() stops as soon as the compressed stream is exhausted
(e.g. a zero chunk header) and returns the number of bytes it actually
wrote, which may be far less than frame_size. The bytes between unc_size
and frame_size are never written. The only memset() that follows zeroes
the region beyond i_valid; when the frame lies entirely within the file's
valid size that memset() does not run, so the gap retains whatever was in
the just-vmapped pages. All pages are then marked uptodate and returned
to userspace, disclosing uninitialized (recently-freed) kernel page
memory. A crafted compressed file whose stream decompresses to only a few
bytes leaks the remainder of every frame on a plain read(2), which is
enough to recover kernel pointers and defeat KASLR.

Zero the [unc_size, frame_size) tail immediately after a successful LZNT
decompress so the remainder reads back as zero.

Fixes: 4342306f0f0d ("fs/ntfs3: Add file operations and implementation")
Cc: stable@vger.kernel.org
Assisted-by: Bynario AI
Signed-off-by: Samuel Page <sam@bynar.io>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

0 files changed, 0 insertions, 0 deletions