UBI: Fix stale pointers in ubi->lookuptbl

In some error paths the WL sub-system gives up on a PEB
and frees it's ubi_wl_entry struct but does not set
the entry in ubi->lookuptbl to NULL.
Fastmap can stumble over such a stale pointer as it uses
ubi->lookuptbl to find all PEBs.

Fix this by introducing a new helper function which free()s
a WL entry and removes the reference from the lookup table.
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/wl.c

@@ -215,6 +215,20 @@ static void wl_tree_add(struct ubi_wl_entry *e, struct rb_root *root)
 	rb_insert_color(&e->u.rb, root);
 }
 
+/**
+ * wl_tree_destroy - destroy a wear-leveling entry.
+ * @ubi: UBI device description object
+ * @e: the wear-leveling entry to add
+ *
+ * This function destroys a wear leveling entry and removes
+ * the reference from the lookup table.
+ */
+static void wl_entry_destroy(struct ubi_device *ubi, struct ubi_wl_entry *e)
+{
+	ubi->lookuptbl[e->pnum] = NULL;
+	kmem_cache_free(ubi_wl_entry_slab, e);
+}
+
 /**
  * do_work - do one pending work.
  * @ubi: UBI device description object
@@ -1258,7 +1272,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 	err = do_sync_erase(ubi, e1, vol_id, lnum, 0);
 	if (err) {
 		if (e2)
-			kmem_cache_free(ubi_wl_entry_slab, e2);
+			wl_entry_destroy(ubi, e2);
 		goto out_ro;
 	}
 
@@ -1326,8 +1340,8 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 	spin_unlock(&ubi->wl_lock);
 
 	ubi_free_vid_hdr(ubi, vid_hdr);
-	kmem_cache_free(ubi_wl_entry_slab, e1);
-	kmem_cache_free(ubi_wl_entry_slab, e2);
+	wl_entry_destroy(ubi, e1);
+	wl_entry_destroy(ubi, e2);
 
 out_ro:
 	ubi_ro_mode(ubi);
@@ -1469,7 +1483,7 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
 	if (shutdown) {
 		dbg_wl("cancel erasure of PEB %d EC %d", pnum, e->ec);
 		kfree(wl_wrk);
-		kmem_cache_free(ubi_wl_entry_slab, e);
+		wl_entry_destroy(ubi, e);
 		return 0;
 	}
 
@@ -1515,7 +1529,7 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
 		return err;
 	}
 
-	kmem_cache_free(ubi_wl_entry_slab, e);
+	wl_entry_destroy(ubi, e);
 	if (err != -EIO)
 		/*
 		 * If this is not %-EIO, we have no idea what to do. Scheduling
@@ -1807,9 +1821,10 @@ int ubi_wl_flush(struct ubi_device *ubi, int vol_id, int lnum)
 
 /**
  * tree_destroy - destroy an RB-tree.
+ * @ubi: UBI device description object
  * @root: the root of the tree to destroy
  */
-static void tree_destroy(struct rb_root *root)
+static void tree_destroy(struct ubi_device *ubi, struct rb_root *root)
 {
 	struct rb_node *rb;
 	struct ubi_wl_entry *e;
@@ -1831,7 +1846,7 @@ static void tree_destroy(struct rb_root *root)
 					rb->rb_right = NULL;
 			}
 
-			kmem_cache_free(ubi_wl_entry_slab, e);
+			wl_entry_destroy(ubi, e);
 		}
 	}
 }
@@ -1962,7 +1977,7 @@ int ubi_wl_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
 		ubi_assert(!ubi_is_fm_block(ubi, e->pnum));
 		ubi->lookuptbl[e->pnum] = e;
 		if (schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0)) {
-			kmem_cache_free(ubi_wl_entry_slab, e);
+			wl_entry_destroy(ubi, e);
 			goto out_free;
 		}
 
@@ -2056,9 +2071,9 @@ int ubi_wl_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
 
 out_free:
 	shutdown_work(ubi);
-	tree_destroy(&ubi->used);
-	tree_destroy(&ubi->free);
-	tree_destroy(&ubi->scrub);
+	tree_destroy(ubi, &ubi->used);
+	tree_destroy(ubi, &ubi->free);
+	tree_destroy(ubi, &ubi->scrub);
 	kfree(ubi->lookuptbl);
 	return err;
 }
@@ -2075,7 +2090,7 @@ static void protection_queue_destroy(struct ubi_device *ubi)
 	for (i = 0; i < UBI_PROT_QUEUE_LEN; ++i) {
 		list_for_each_entry_safe(e, tmp, &ubi->pq[i], u.list) {
 			list_del(&e->u.list);
-			kmem_cache_free(ubi_wl_entry_slab, e);
+			wl_entry_destroy(ubi, e);
 		}
 	}
 }
@@ -2107,10 +2122,10 @@ void ubi_wl_close(struct ubi_device *ubi)
 	ubi_fastmap_close(ubi);
 	shutdown_work(ubi);
 	protection_queue_destroy(ubi);
-	tree_destroy(&ubi->used);
-	tree_destroy(&ubi->erroneous);
-	tree_destroy(&ubi->free);
-	tree_destroy(&ubi->scrub);
+	tree_destroy(ubi, &ubi->used);
+	tree_destroy(ubi, &ubi->erroneous);
+	tree_destroy(ubi, &ubi->free);
+	tree_destroy(ubi, &ubi->scrub);
 	kfree(ubi->lookuptbl);
 }