[PATCH v2] ocfs2/heartbeat: Unlink live slots when their node is missing

[Cen Zhang]

o2hb_shutdown_slot() returns immediately when its node is no longer
in the configfs registry. A slot can still be linked in o2hb_live_slots
when that lookup fails. Region teardown or startup-error cleanup then
frees the slot array without removing its embedded list member.

With the same peer live in another region, the next list update can
follow a predecessor into the freed array. Reusing the node number can
also make a later insertion encounter that stale member.

Always remove the slot under o2hb_live_lock, even when node lookup
fails. Preserve aggregate membership accounting and the last-region
DOWN callback: the existing callback interface explicitly permits a
NULL node for DOWN events. Only drop the node reference when lookup
returned one. This closes both normal release and startup-abort paths
without changing the publication or callback locking protocol.

Also require a configured node before admitting a new live slot in
o2hb_check_slot(). The early live-bitmap check is not held through
admission: the last live slot in another region can be removed in
between. Without a node, admission can then queue an UP event with
a NULL argument and hit the event helper's BUG_ON. Existing live
slots can still leave and generate NULL-node DOWN events.

A controlled probe-instrumented test reproduced this while stopping
one of two regions after removing the peer from configfs. Its KASAN
report includes:

  BUG: KASAN: slab-use-after-free in __list_del_entry_valid_or_report+0x1e0/0x210
  Read of size 8 at addr ffff888106a4ac60 by task o2hb-pmbd0058_b/497
  Call Trace:
   <TASK>
   dump_stack_lvl+0x93/0xd0
   print_report+0xce/0x630
   kasan_report+0xe0/0x110
   __list_del_entry_valid_or_report+0x1e0/0x210
   o2hb_do_disk_heartbeat+0x1591/0x2c50
   o2hb_thread+0x1ed/0xe70
   kthread+0x351/0x460
   ret_from_fork+0x659/0x940
   ret_from_fork_asm+0x1a/0x30
   </TASK>
  Allocated by task 491:
   kasan_save_stack+0x33/0x60
   kasan_save_track+0x14/0x30
   __kasan_kmalloc+0xaa/0xb0
   __kmalloc_noprof+0x2de/0x780
   o2hb_region_dev_store+0x7c2/0x1b60
   configfs_write_iter+0x2f9/0x4f0
   vfs_write+0x639/0x1010
   ksys_write+0x111/0x200
   do_syscall_64+0x114/0x620
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Freed by task 491:
   kasan_save_stack+0x33/0x60
   kasan_save_track+0x14/0x30
   kasan_save_free_info+0x3b/0x60
   __kasan_slab_free+0x5f/0x80
   kfree+0x308/0x580
   o2hb_unmap_slot_data+0x1db/0x330
   o2hb_region_release+0x14b/0x4f0
   config_item_cleanup+0x14b/0x230
   config_item_put+0x79/0x90
   configfs_rmdir+0x58a/0x910
   vfs_rmdir+0x2e8/0x820
   filename_rmdir+0x3b1/0x520
   __x64_sys_rmdir+0x4b/0x70
   do_syscall_64+0x114/0x620
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: a7f6a5fb4bde ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Assisted-by: LLM
Signed-off-by: Cen Zhang <zzzccc427@xxxxxxxxx>
---
Changes in v2:
- Require a configured node before admitting a live slot in
  o2hb_check_slot().

Link to v1: https://lore.kernel.org/r/pm-ocfs2-objects-candidate-0058-v1-177573785904d0ea43c7@xxxxxxxxx

 fs/ocfs2/cluster/heartbeat.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
index 1c3def99bb0765deb828ad6415fde31ed9316002..3f3f6fc6b1316e7c996681fc50fde84d183d117d 100644
--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c
@@ -880,8 +880,11 @@ static void o2hb_shutdown_slot(struct o2hb_disk_slot *slot)
 	int queued = 0;
 
 	node = o2nm_get_node_by_num(slot->ds_node_num);
-	if (!node)
-		return;
+	/*
+	 * The node may have been removed from the node table while this
+	 * region's slot is still linked.  The list member must still be
+	 * removed before the region releases its slot array.
+	 */
 
 	spin_lock(&o2hb_live_lock);
 	if (!list_empty(&slot->ds_live_item)) {
@@ -903,7 +906,8 @@ static void o2hb_shutdown_slot(struct o2hb_disk_slot *slot)
 	if (queued)
 		o2hb_run_event_list(&event);
 
-	o2nm_node_put(node);
+	if (node)
+		o2nm_node_put(node);
 }
 
 static void o2hb_set_quorum_device(struct o2hb_region *reg)
@@ -1038,7 +1042,7 @@ static int o2hb_check_slot(struct o2hb_region *reg,
 fire_callbacks:
 	/* dead nodes only come to life after some number of
 	 * changes at any time during their dead time */
-	if (list_empty(&slot->ds_live_item) &&
+	if (node && list_empty(&slot->ds_live_item) &&
 	    slot->ds_changed_samples >= O2HB_LIVE_THRESHOLD) {
 		mlog(ML_HEARTBEAT, "Node %d (id 0x%llx) joined my region\n",
 		     slot->ds_node_num, (long long)slot->ds_last_generation);