CVE-2026-98125: smb/client: fix stale page cache in insert/collapse range
In the Linux kernel, the following vulnerability has been resolved:
smb/client: fix stale page cache in insert/collapse range
smb3insertrange() and smb3collapserange() use truncatepagecacherange() to invalidate the affected page cache. However, if off or oldeof is not page-aligned, the boundary pages are only partially zeroed and remain uptodate. As a result, the client may return stale data after a successful insert/collapse range operation.
For example, with 4K pages:
page 0 page 1 page 2 0------4K 4K------8K 8K------12K ^ ^ off=2K oldeof=10K
Page 1 is removed from the page cache, while the boundary pages are only partially zeroed. After COPYCHUNK moves the data on the server, these cached pages may still return stale data.
This can be reproduced on a CIFS mount:
bash -c ' FILE=/mnt/scratch/repro
# Use a 6 KiB file so EOF is not page-aligned. dd if=/dev/urandom of=/tmp/src bs=1K count=6 status=none
# Expected: a 4 KiB hole followed by the original data. rm -f /tmp/expected truncate -s 4K /tmp/expected cat /tmp/src >> /tmp/expected
cp /tmp/src "$FILE"
# Prime the page cache before moving data on the server. cat "$FILE" > /dev/null
fallocate --insert-range -o 0 -l 4K "$FILE"
if cmp -s /tmp/expected "$FILE"; then echo "readback: OK" else echo "readback: STALE DATA" fi '
Fix this by writing back dirty data and discarding the page cache from the start of the page containing off to EOF before moving data on the server.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Operational
Before moving data on the server, write back dirty data and discard the affected page cache from the start of the page containing the offset through EOF.
Event History
Frequently Asked Questions
Which systems are exposed to stale reads?
Systems using a CIFS/SMB client mount can be affected when SMB range insert or collapse operations are performed with offsets or prior EOF values that are not page-aligned. The issue concerns client page-cache contents after the server-side data movement succeeds.
What conditions are needed to observe the problem?
The relevant file data must already be present in the client page cache before an insert-range or collapse-range operation. A non-page-aligned boundary is also needed, because the boundary cache pages can be only partially zeroed while remaining marked up-to-date.
How can an administrator determine whether a system is affected?
On a CIFS mount, create a file whose EOF is not page-aligned, read it to prime the page cache, then perform an insert-range or collapse-range operation and read the result. If cached boundary data differs from the expected post-operation contents, the client is returning stale data.