CVE-2026-68155libceph: Reject monmaps advertising zero monitors

Official description

In the Linux kernel, the following vulnerability has been resolved: libceph: Reject monmaps advertising zero monitors A message of type CEPH_MSG_MON_MAP contains a monmap that is sent from a monitor to the client. This monmap contains information about the existing monitors in the cluster. Currently, a monmap indicating that there are zero monitors in the cluster is treated as valid. However, it is impossible to have zero monitors in the cluster and still receive a valid monmap from a monitor. Therefore, such a monmap must be corrupted and should be treated as invalid. Furthermore, a monmap with a monitor count of zero can subsequently crash the client when attempting to open a session with a monitor in __open_session(). This happens because the "BUG_ON(monc->monmap->num_mon < 1)" assertion in pick_new_mon() is triggered. This patch extends a check in ceph_monmap_decode() to also reject arriving mon_maps with num_mon == 0 rather than only with num_mon > CEPH_MAX_MON. [ idryomov: drop "log output for unusual values of num_mon" part ]

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ba5f0015bfd376d764163045a61c17be75f44dae
• https://git.kernel.org/stable/c/caf082ef8609a6ac26159ce115f55ab7d00231a3
• https://git.kernel.org/stable/c/e3ccd4ecab09b22f507f49cb7ed9990c7158ceab
• https://git.kernel.org/stable/c/0591a15815b498be628a937146e44487d599ba33
• https://git.kernel.org/stable/c/cd0d41bc569632eaaeccde9d2a6bc919ec00c407
• https://git.kernel.org/stable/c/e67e8b694872c9bc66996040f9de9242f6236ed9
• https://git.kernel.org/stable/c/3b249546f59c3d6d3592c10657f82bc3f1faa07c
• https://git.kernel.org/stable/c/40480eee361ed9676b3f844d532ac28b47251634