btrfs: fix possible leak in btrfs_ioctl_balance()

Commit 8eb934591f ("btrfs: check unsupported filters in balance
arguments") adds a jump to exit label out_bargs in case the argument
check fails. At this point in addition to the bargs memory, the
memory for struct btrfs_balance_control has already been allocated.
Ownership of bctl is passed to btrfs_balance() in the good case,
thus the memory is not freed due to the introduced jump. Make sure
that the memory gets freed in any case as necessary. Detected by
Coverity CID 1328378.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ioctl.c

@@ -4641,7 +4641,7 @@ locked:
 
 	if (bctl->flags & ~(BTRFS_BALANCE_ARGS_MASK | BTRFS_BALANCE_TYPE_MASK)) {
 		ret = -EINVAL;
-		goto out_bargs;
+		goto out_bctl;
 	}
 
 do_balance:
@@ -4655,12 +4655,15 @@ do_balance:
 	need_unlock = false;
 
 	ret = btrfs_balance(bctl, bargs);
+	bctl = NULL;
 
 	if (arg) {
 		if (copy_to_user(arg, bargs, sizeof(*bargs)))
 			ret = -EFAULT;
 	}
 
+out_bctl:
+	kfree(bctl);
 out_bargs:
 	kfree(bargs);
 out_unlock: