Re: [PATCH] media: dvb_ringbuffer: Return -EFAULT if copy fails

[Dan Carpenter]

On Wed, May 24, 2023 at 09:27:33AM +0800, Su Hui wrote:
> The copy_to/from_user() functions return the number of bytes remaining
> to be copied, but we want to return -EFAULT to the user.
> 
> Fixes: 04da2daee383 ("[media] ngene: properly handle __user ptr")
> Signed-off-by: Su Hui <suhui@xxxxxxxxxxxx>
> ---
>  drivers/media/dvb-core/dvb_ringbuffer.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c
> index 7d4558de8e83..f132578840ad 100644
> --- a/drivers/media/dvb-core/dvb_ringbuffer.c
> +++ b/drivers/media/dvb-core/dvb_ringbuffer.c
> @@ -216,7 +216,7 @@ ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf,
>  	if (split > 0) {
>  		status = copy_from_user(rbuf->data+rbuf->pwrite, buf, split);
>  		if (status)
> -			return len - todo;
> +			return -EFAULT;

No no no.  This is obviously deliberate.  It's returning the number of
bytes that were successfully copied.

(I'm not sure I like this API.  If buf is a bad address then shouldn't
we report that to the user?  It's not like we ran out of space or hit
some limit in the kernel, it's just a bug in the user space program.
However, changing the API is dangerous and could break user space).

Same for the other.

regards,
dan carpenter