fs/ntfs3: fix missing run load for vcn0 in attr_data_get_block_locked()

When a compressed or sparse attribute has its clusters frame-aligned,
vcn is rounded down to the frame start using cmask, which can result
in vcn != vcn0. In this case, vcn and vcn0 may reside in different
attribute segments.

The code already handles the case where vcn is in a different segment
by loading its runs before allocation. However, it fails to load runs
for vcn0 when vcn0 resides in a different segment than vcn. This causes
run_lookup_entry() to return SPARSE_LCN for vcn0 since its segment was
never loaded into the in-memory run list, triggering the WARN_ON(1).

Fix this by adding a missing check for vcn0 after the existing vcn
segment check. If vcn0 falls outside the current segment range
[svcn, evcn1), find and load the attribute segment containing vcn0
before performing the run lookup.

The following scenario triggers the bug:
  attr_data_get_block_locked()
    vcn = vcn0 & cmask        <- vcn != vcn0 after frame alignment
    load runs for vcn segment <- vcn0 segment not loaded!
    attr_allocate_clusters()  <- allocation succeeds
    run_lookup_entry(vcn0)    <- vcn0 not in run -> SPARSE_LCN
    WARN_ON(1)                <- bug fires here!

Reported-by: syzbot+c1e9aedbd913fadad617@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c1e9aedbd913fadad617
Fixes: c380b52f6c57 ("fs/ntfs3: Change new sparse cluster processing")
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

0 files changed, 0 insertions, 0 deletions