Re: [PATCH] block: Clear kernel memory before copying to user

[Ming Lei <tom.leiming@xxxxxxxxx>]

On Wed, Nov 7, 2018 at 10:42 PM Keith Busch <keith.busch@xxxxxxxxx> wrote:
>
> If the kernel allocates a bounce buffer for user read data, this memory
> needs to be cleared before copying it to the user, otherwise it may leak
> kernel memory to user space.
>
> Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
> ---
>  block/bio.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/block/bio.c b/block/bio.c
> index d5368a445561..a50d59236b19 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1260,6 +1260,7 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
>                 if (ret)
>                         goto cleanup;
>         } else {
> +               zero_fill_bio(bio);
>                 iov_iter_advance(iter, bio->bi_iter.bi_size);
>         }

This way looks inefficient because zero fill should only be required
for short READ.

Thanks,
Ming Lei