Hello, We are encountering a reproducible issue with the CephFS kernel client on Ubuntu 24.04 and would appreciate your feedback. Context: We are preparing an updated Ubuntu 24.04 image for our scientific users. With kernel |6.17.0-14-generic|, the CephFS mount succeeds and the filesystem is visible via |df -h|, but any attempt to access the directory contents (e.g. |ls|) immediately triggers a kernel crash. From userland, the process is simply killed: |# ls /net/serdon/illdata Killed| The mount appears healthy and the filesystem is correctly reported: |# mount | grep ceph 192.168.170.61,192.168.170.69,192.168.170.70:/ on /net/serdon/illdata type ceph (rw,relatime,name=visa,acl) # df -h | grep serdon 192.168.170.61,192.168.170.69,192.168.170.70:/ 4.1P 2.0P 2.1P 49% /net/serdon/illdata| However, any access to the mount point triggers a kernel NULL pointer dereference in the Ceph module: |BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: strcmp+0x10/0x40 Call Trace: ceph_mds_auth_match ceph_mds_check_access ceph_open| Environment: |Linux 6.17.0-14-generic #14~24.04.1-Ubuntu CephFS mounted via kernel client (mount -t ceph)| The issue is fully reproducible: any access to the mount point causes the same kernel crash. Full stack trace: https://pastebin.com/ZgQHpN0q <https://pastebin.com/ZgQHpN0q> Questions: - Is this a known issue with the CephFS kernel client on Linux 6.17? - Does this look like an upstream CephFS bug, or something specific to the Ubuntu 6.17 kernel? We can provide additional details (Ceph cluster version, MDS version, etc.) if needed. Thank you for your help. Best regards, Fabien