Forwarded: [PATCH] fs/ntfs3: fix missing run load for vcn0 in attr_data_get_block_locked()

syzbot
2026-03-19T05:52:59Z

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] fs/ntfs3: fix missing run load for vcn0 in attr_data_get_block_locked()
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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
Link: https://syzkaller.appspot.com/bug?extid=c1e9aedbd913fadad617
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
---
fs/ntfs3/attrib.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/fs/ntfs3/attrib.c b/fs/ntfs3/attrib.c
index 6cb9bc5d605c..6ef7db82a35d 100644
--- a/fs/ntfs3/attrib.c
+++ b/fs/ntfs3/attrib.c
@@ -1152,6 +1152,20 @@ int attr_data_get_block_locked(struct ntfs_inode *ni, CLST vcn, CLST clen,
if (err)
goto out;
}
+
+ if (vcn0 < svcn || evcn1 <= vcn0) {
+ struct ATTRIB *attr2;
+ attr2 = ni_find_attr(ni, attr_b, &le_b, ATTR_DATA, NULL,
+ 0, &vcn0, &mi);
+ if (!attr2) {
+ err = -EINVAL;
+ goto out;
+ }
+ err = attr_load_runs(attr2, ni, run, NULL);
+ if (err)
+ goto out;
+ }
+
da = false; /* no delalloc for compressed file. */
}

--
2.43.0