Re: [PATCH] Btrfs: do not overwrite error return value in scrub progress ioctl

Nikolay Borisov
2018-12-17T07:33:48Z

On 14.12.18 г. 21:45 ч., fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
>
> If the call to btrfs_scrub_progress() failed we would overwrite the error
> returned to user space with -EFAULT if the call to copy_to_user() failed
> as well. Fix that by calling copy_to_user() only if btrfs_scrub_progress()
> returned success.
>
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
> fs/btrfs/ioctl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 01d18e1a393e..76848214a39f 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -4331,7 +4331,7 @@ static long btrfs_ioctl_scrub_progress(struct btrfs_fs_info *fs_info,
>
> ret = btrfs_scrub_progress(fs_info, sa->devid, &sa->progress);
>
> - if (copy_to_user(arg, sa, sizeof(*sa)))
> + if (ret == 0 && copy_to_user(arg, sa, sizeof(*sa)))

While this is ok it's a bit counter intuitive considering the code
convention. Because you predicate the execution of copy_to_user on the
ret value of btrfs_scrub_progress in the same if. Perhaps,

if (ret)
return ret;

if (copy_to_user)
return -EFAULT

Same feedback applies to your other patches, but I'm fine if you leave
it as is so:

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ret = -EFAULT;
>
> kfree(sa);
>