CVE-2026-98124smb/client: invalidate fscache for fallocate range operations

Official description

In the Linux kernel, the following vulnerability has been resolved: smb/client: invalidate fscache for fallocate range operations smb3_zero_range(), smb3_punch_hole(), smb3_insert_range(), and smb3_collapse_range() modify file contents through server-side range operations. These operations discard the affected page cache, but leave the FS-Cache cookie valid, so a later read may return data cached before the range operation. Fix this by invalidating FS-Cache after outstanding I/O has completed and before modifying the file on the server. Run the following as root on a CIFS mount with fsc enabled and an active CacheFiles backend: bash -c ' MNT=/mnt/cifs FILE="$MNT/repro" # Generate four 1 MiB random blocks: [A][B][C][D]. dd if=/dev/urandom of=/tmp/src bs=1M count=4 status=none # Expected contents after zeroing B: [A][zero][C][D]. cp /tmp/src /tmp/expected dd if=/dev/zero of=/tmp/expected bs=1M seek=1 count=1 \ conv=notrunc status=none cp /tmp/src "$FILE" # Populate FS-Cache, then discard the page cache. sync echo 1 > /proc/sys/vm/drop_caches cat "$FILE" > /dev/null sync echo 1 > /proc/sys/vm/drop_caches fallocate --zero-range -o 1M -l 1M "$FILE" if cmp -s /tmp/expected "$FILE"; then echo "readback: OK" else echo "readback: STALE DATA" fi ' Before this change, the readback differs from /tmp/expected: readback: STALE DATA After this change, it matches: readback: OK

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/cc7202a51b8777a757bda9dcfbf339f828c6a130
• https://git.kernel.org/stable/c/dd8b1e808f5c19479e6ed47e2f88a1fd46f8b0e5
• https://git.kernel.org/stable/c/93c6e5a8d7c5071d586c1411596d5db5faad22b2
• https://git.kernel.org/stable/c/448ba0ae65ca61064183564d2983c9aa59bd6ba7