ubifs: Fix memory leak of bud->log_hash

Ensure that the allocated bud->log_hash (if any) is freed in all cases
when the bud itself is freed, to fix this leak caught by kmemleak:

 # keyctl add logon foo:bar data @s
 # echo clear > /sys/kernel/debug/kmemleak
 # mount -t ubifs /dev/ubi0_0 mnt -o auth_hash_name=sha256,auth_key=foo:bar
 # echo a > mnt/x
 # umount mnt
 # mount -t ubifs /dev/ubi0_0 mnt -o auth_hash_name=sha256,auth_key=foo:bar
 # umount mnt
 # sleep 5
 # echo scan > /sys/kernel/debug/kmemleak
 # echo scan > /sys/kernel/debug/kmemleak
 # cat /sys/kernel/debug/kmemleak
 unreferenced object 0xff... (size 128):
   comm "mount"
   backtrace:
     __kmalloc
     __ubifs_hash_get_desc+0x5d/0xe0 ubifs
     ubifs_replay_journal
     ubifs_mount
     ...

Fixes: da8ef65f ("ubifs: Authenticate replayed journal")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/super.c

@@ -923,8 +923,10 @@ static void free_buds(struct ubifs_info *c)
 {
 	struct ubifs_bud *bud, *n;
 
-	rbtree_postorder_for_each_entry_safe(bud, n, &c->buds, rb)
+	rbtree_postorder_for_each_entry_safe(bud, n, &c->buds, rb) {
+		kfree(bud->log_hash);
 		kfree(bud);
+	}
 }
 
 /**
@@ -1193,6 +1195,7 @@ static void destroy_journal(struct ubifs_info *c)
 
 		bud = list_entry(c->old_buds.next, struct ubifs_bud, list);
 		list_del(&bud->list);
+		kfree(bud->log_hash);
 		kfree(bud);
 	}
 	ubifs_destroy_idx_gc(c);