ubifs: dbg_check_idx_size: Fix kmemleak if loading znode failed

If function dbg_check_idx_size() failed by loading znode in mounting
process, there are two problems:
  1. Allocated znodes won't be freed, which causes kmemleak in kernel:
     ubifs_mount
      dbg_check_idx_size
       dbg_walk_index
        c->zroot.znode = ubifs_load_znode
	child = ubifs_load_znode // failed
	// Loaded znodes won't be freed in error handling path.
  2. Global variable ubifs_clean_zn_cnt is not decreased, because
     ubifs_tnc_close() is not invoked in error handling path, which
     triggers a warning in ubifs_exit():
      WARNING: CPU: 1 PID: 1576 at fs/ubifs/super.c:2486 ubifs_exit
      Modules linked in: zstd ubifs(-) ubi nandsim
      CPU: 1 PID: 1576 Comm: rmmod Not tainted 6.7.0-rc6
      Call Trace:
	ubifs_exit+0xca/0xc70 [ubifs]
	__do_sys_delete_module+0x29a/0x4a0
	do_syscall_64+0x6f/0x140

Fix it by adding error handling path in dbg_check_idx_size() to release
tnc tree.

Fixes: 1e51764a3c ("UBIFS: add new flash file system")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Suggested-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/debug.c

@@ -1742,17 +1742,22 @@ int dbg_check_idx_size(struct ubifs_info *c, long long idx_size)
 	err = dbg_walk_index(c, NULL, add_size, &calc);
 	if (err) {
 		ubifs_err(c, "error %d while walking the index", err);
-		return err;
+		goto out_err;
 	}
 
 	if (calc != idx_size) {
 		ubifs_err(c, "index size check failed: calculated size is %lld, should be %lld",
 			  calc, idx_size);
 		dump_stack();
-		return -EINVAL;
+		err = -EINVAL;
+		goto out_err;
 	}
 
 	return 0;
+
+out_err:
+	ubifs_destroy_tnc_tree(c);
+	return err;
 }
 
 /**

fs/ubifs/tnc.c

@@ -3116,14 +3116,7 @@ static void tnc_destroy_cnext(struct ubifs_info *c)
 void ubifs_tnc_close(struct ubifs_info *c)
 {
 	tnc_destroy_cnext(c);
-	if (c->zroot.znode) {
-		long n, freed;
-
-		n = atomic_long_read(&c->clean_zn_cnt);
-		freed = ubifs_destroy_tnc_subtree(c, c->zroot.znode);
-		ubifs_assert(c, freed == n);
-		atomic_long_sub(n, &ubifs_clean_zn_cnt);
-	}
+	ubifs_destroy_tnc_tree(c);
 	kfree(c->gap_lebs);
 	kfree(c->ilebs);
 	destroy_old_idx(c);

fs/ubifs/tnc_misc.c

@@ -250,6 +250,28 @@ long ubifs_destroy_tnc_subtree(const struct ubifs_info *c,
 	}
 }
 
+/**
+ * ubifs_destroy_tnc_tree - destroy all znodes connected to the TNC tree.
+ * @c: UBIFS file-system description object
+ *
+ * This function destroys the whole TNC tree and updates clean global znode
+ * count.
+ */
+void ubifs_destroy_tnc_tree(struct ubifs_info *c)
+{
+	long n, freed;
+
+	if (!c->zroot.znode)
+		return;
+
+	n = atomic_long_read(&c->clean_zn_cnt);
+	freed = ubifs_destroy_tnc_subtree(c, c->zroot.znode);
+	ubifs_assert(c, freed == n);
+	atomic_long_sub(n, &ubifs_clean_zn_cnt);
+
+	c->zroot.znode = NULL;
+}
+
 /**
  * read_znode - read an indexing node from flash and fill znode.
  * @c: UBIFS file-system description object

fs/ubifs/ubifs.h

@@ -1903,6 +1903,7 @@ struct ubifs_znode *ubifs_tnc_postorder_next(const struct ubifs_info *c,
 					     struct ubifs_znode *znode);
 long ubifs_destroy_tnc_subtree(const struct ubifs_info *c,
 			       struct ubifs_znode *zr);
+void ubifs_destroy_tnc_tree(struct ubifs_info *c);
 struct ubifs_znode *ubifs_load_znode(struct ubifs_info *c,
 				     struct ubifs_zbranch *zbr,
 				     struct ubifs_znode *parent, int iip);