[PATCH] ocfs2/dlm: serialize migration MLE cleanup on failure

[Cen Zhang <zzzccc427@gmail.com>]

A migration MLE has a base reference for the mastering answer and an
in-use reference held by dlm_migrate_lockres(). The finishing assertion
consumes the base reference, but migration failure drops it again
without checking whether the assertion already consumed it.

The target queues its migration worker before it acknowledges the
ALL_DONE packet, so its finishing assertion can arrive while the sender
still waits for the status, or after dlm_send_one_lockres() has
returned a connection error for that very packet:

  Old-master sender                  Finishing assertion
  -----------------                  -------------------
  publish MLE; take in-use reference
  send ALL_DONE; wait for status
                                     take lookup reference
                                     unlink MLE
                                     put lookup and base references
  send returns a connection error
  put base reference again; free MLE
  put in-use reference; access freed MLE

dlm_assert_master_handler() holds dlm->spinlock from the MLE lookup to
the final puts, and it takes dlm->master_lock around the unlink and the
puts. Decide under the same locks: if the MLE is already unhashed, the
assertion consumed the base reference, so drop only the sender's in-use
reference. Otherwise unlink it before consuming the base reference so a
later assertion no longer finds it.

Use the same cleanup helper for the pre-send failure, the send failure
and the target-death failure paths. The sender's in-use reference keeps
the MLE alive until its final put outside the nested locks. Successful
migration retains its existing in-use-only put.

KASAN report, only the relevant frames are kept:

BUG: KASAN: slab-use-after-free in dlm_put_mle_inuse+0xce/0xe0
Read of size 8 at addr ffff8881190e3c20 by task umount/593

Call Trace:
 <TASK>
 dlm_put_mle_inuse+0xce/0xe0
 dlm_migrate_lockres+0x16af/0x20d0
 dlm_empty_lockres+0x60a/0xbd0
 dlm_unregister_domain+0x53b/0x11d0
 o2cb_cluster_disconnect+0xa5/0x110
 ocfs2_cluster_disconnect+0x73/0xc0
 ocfs2_dlm_shutdown+0x311/0x440
 ocfs2_dismount_volume+0x696/0x940
 generic_shutdown_super+0x15f/0x490
 kill_block_super+0x40/0xa0
 deactivate_locked_super+0xae/0x120
 deactivate_super+0xa2/0xc0
 cleanup_mnt+0x217/0x450
 task_work_run+0x144/0x230
 </TASK>

Allocated by task 593:
 kmem_cache_alloc_noprof+0x20b/0x5c0
 dlm_migrate_lockres+0x20e/0x20d0
 dlm_empty_lockres+0x60a/0xbd0
 dlm_unregister_domain+0x53b/0x11d0
 o2cb_cluster_disconnect+0xa5/0x110
 ocfs2_cluster_disconnect+0x73/0xc0
 ocfs2_dlm_shutdown+0x311/0x440
 ocfs2_dismount_volume+0x696/0x940

Freed by task 593:
 kmem_cache_free+0x242/0x580
 __dlm_put_mle+0x4b2/0x660
 dlm_migrate_lockres+0x1690/0x20d0
 dlm_empty_lockres+0x60a/0xbd0
 dlm_unregister_domain+0x53b/0x11d0
 o2cb_cluster_disconnect+0xa5/0x110
 ocfs2_cluster_disconnect+0x73/0xc0
 ocfs2_dlm_shutdown+0x311/0x440

The buggy address belongs to the object at ffff8881190e3c00
 which belongs to the cache o2dlm_mle of size 480
The buggy address is located 32 bytes inside of
 freed 480-byte region [ffff8881190e3c00, ffff8881190e3de0)

Fixes: 6714d8e86bf4 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 fs/ocfs2/dlm/dlmmaster.c | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index 612969867ff9..57119b195cc1 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -2525,6 +2525,27 @@ static int dlm_is_lockres_migratable(struct dlm_ctxt *dlm,
  */
 
 
+/*
+ * The finishing assert may already have unlinked the MLE and dropped its
+ * base reference. Decide under the locks the assert handler holds, and only
+ * drop the base reference here while the MLE is still hashed.
+ */
+static void dlm_put_migration_mle(struct dlm_ctxt *dlm,
+				  struct dlm_master_list_entry *mle)
+{
+	spin_lock(&dlm->spinlock);
+	spin_lock(&dlm->master_lock);
+	__dlm_mle_detach_hb_events(dlm, mle);
+	if (!hlist_unhashed(&mle->master_hash_node)) {
+		__dlm_unlink_mle(dlm, mle);
+		__dlm_put_mle(mle);
+	}
+	spin_unlock(&dlm->master_lock);
+	spin_unlock(&dlm->spinlock);
+
+	dlm_put_mle_inuse(mle);
+}
+
 static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
 			       struct dlm_lock_resource *res, u8 target)
 {
@@ -2609,9 +2630,7 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
 
 	if (ret < 0) {
 		if (mle_added) {
-			dlm_mle_detach_hb_events(dlm, mle);
-			dlm_put_mle(mle);
-			dlm_put_mle_inuse(mle);
+			dlm_put_migration_mle(dlm, mle);
 		} else if (mle) {
 			kmem_cache_free(dlm_mle_cache, mle);
 			mle = NULL;
@@ -2640,9 +2659,7 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
 		mlog(0, "migration to node %u failed with %d\n",
 		     target, ret);
 		/* migration failed, detach and clean up mle */
-		dlm_mle_detach_hb_events(dlm, mle);
-		dlm_put_mle(mle);
-		dlm_put_mle_inuse(mle);
+		dlm_put_migration_mle(dlm, mle);
 		spin_lock(&res->spinlock);
 		res->state &= ~DLM_LOCK_RES_MIGRATING;
 		wake = 1;
@@ -2686,9 +2703,7 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
 				     res->lockname.name, target);
 				ret = -EINVAL;
 				/* migration failed, detach and clean up mle */
-				dlm_mle_detach_hb_events(dlm, mle);
-				dlm_put_mle(mle);
-				dlm_put_mle_inuse(mle);
+				dlm_put_migration_mle(dlm, mle);
 				spin_lock(&res->spinlock);
 				res->state &= ~DLM_LOCK_RES_MIGRATING;
 				wake = 1;