CVE-2026-23201: ceph: fix oops due to invalid pointer for kfree() in parse_longname()

In the Linux kernel, the following vulnerability has been resolved:

ceph: fix oops due to invalid pointer for kfree() in parselongname()

This fixes a kernel oops when reading ceph snapshot directories (.snap), for example by simply running ls /mnt/myceph/.snap.

The variable str is guarded by free(kfree), but advanced by one for skipping the initial '' in snapshot names. Thus, kfree() is called with an invalid pointer. This patch removes the need for advancing the pointer so kfree() is called with correct memory pointer.

Steps to reproduce:

1. Create snapshots on a cephfs volume (I've 63 snaps in my testcase)

2. Add cephfs mount to fstab $ echo "samba-fileserver@.files=/volumes/datapool/stuff/3461082b-ecc9-4e82-8549-3fd2590d3fb6 /mnt/test/stuff ceph acl,noatime,netdev 0 0" >> /etc/fstab

3. Reboot the system $ systemctl reboot

4. Check if it's really mounted $ mount | grep stuff

5. List snapshots (expected 63 snapshots on my system) $ ls /mnt/test/stuff/.snap

Now ls hangs forever and the kernel log shows the oops.