From 40480eee361ed9676b3f844d532ac28b47251634 Mon Sep 17 00:00:00 2001 From: Raphael Zimmer Date: Fri, 29 May 2026 09:42:57 +0200 Subject: [PATCH] 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 ] Cc: stable@vger.kernel.org Signed-off-by: Raphael Zimmer Reviewed-by: Ilya Dryomov Signed-off-by: Ilya Dryomov --- net/ceph/mon_client.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c index d2cdc8ee3155..24acdd580e79 100644 --- a/net/ceph/mon_client.c +++ b/net/ceph/mon_client.c @@ -114,7 +114,7 @@ static struct ceph_monmap *ceph_monmap_decode(void **p, void *end, bool msgr2) dout("%s fsid %pU epoch %u num_mon %u\n", __func__, &fsid, epoch, num_mon); - if (num_mon > CEPH_MAX_MON) + if (num_mon == 0 || num_mon > CEPH_MAX_MON) goto e_inval; monmap = kmalloc_flex(*monmap, mon_inst, num_mon, GFP_NOIO);