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 ]
References
- https://git.kernel.org/stable/c/0591a15815b498be628a937146e44487d599ba33
- https://git.kernel.org/stable/c/3b249546f59c3d6d3592c10657f82bc3f1faa07c
- https://git.kernel.org/stable/c/40480eee361ed9676b3f844d532ac28b47251634
- https://git.kernel.org/stable/c/cd0d41bc569632eaaeccde9d2a6bc919ec00c407
- https://git.kernel.org/stable/c/e67e8b694872c9bc66996040f9de9242f6236ed9