Re: [RFC] bio: fix page leak bio_add_hw_page failure

[Pavel Begunkov <asml.silence@gmail.com>]

On 7/19/21 11:53 AM, Pavel Begunkov wrote:
> __bio_iov_append_get_pages() doesn't put not appended pages on
> bio_add_hw_page() failure, so potentially leaking them, fix it. Also, do
> the same for __bio_iov_iter_get_pages(), even though it looks like it
> can't be triggered by userspace in this case.

Any comments?

> 
> Fixes: 0512a75b98f8 ("block: Introduce REQ_OP_ZONE_APPEND")
> Cc: stable@vger.kernel.org # 5.8+
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> 
> I haven't tested the fail path, thus RFC. Would be great if someone can
> do it or take over the fix.
> 
>  block/bio.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 1fab762e079b..d95e3456ba0c 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -979,6 +979,14 @@ static int bio_iov_bvec_set_append(struct bio *bio, struct iov_iter *iter)
>  	return 0;
>  }
>  
> +static void bio_put_pages(struct page **pages, size_t size, size_t off)
> +{
> +	size_t i, nr = DIV_ROUND_UP(size + (off & ~PAGE_MASK), PAGE_SIZE);
> +
> +	for (i = 0; i < nr; i++)
> +		put_page(pages[i]);
> +}
> +
>  #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
>  
>  /**
> @@ -1023,8 +1031,10 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  			if (same_page)
>  				put_page(page);
>  		} else {
> -			if (WARN_ON_ONCE(bio_full(bio, len)))
> -                                return -EINVAL;
> +			if (WARN_ON_ONCE(bio_full(bio, len))) {
> +				bio_put_pages(pages + i, left, offset);
> +				return -EINVAL;
> +			}
>  			__bio_add_page(bio, page, len, offset);
>  		}
>  		offset = 0;
> @@ -1069,6 +1079,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter)
>  		len = min_t(size_t, PAGE_SIZE - offset, left);
>  		if (bio_add_hw_page(q, bio, page, len, offset,
>  				max_append_sectors, &same_page) != len) {
> +			bio_put_pages(pages + i, left, offset);
>  			ret = -EINVAL;
>  			break;
>  		}
> 

-- 
Pavel Begunkov