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

Browse source

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: c380b52f6c ("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>

...

This commit is contained in:

Deepanshu Kartikey 2026-03-19 13:15:46 +05:30 • committed by Konstantin Komarov

parent 81ad9e67ec

commit d7ea8495fd

No known key found for this signature in database

GPG key ID: A9B0331F832407B6

1 changed files with 15 additions and 0 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

15

fs/ntfs3/attrib.c

View file