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

From: Ming Lei <ming.lei@redhat.com>
To: Pavel Begunkov <asml.silence@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Keith Busch <kbusch@kernel.org>
Subject: Re: [RFC] bio: fix page leak bio_add_hw_page failure
Date: Mon, 19 Jul 2021 23:34:09 +0800	[thread overview]
Message-ID: <YPWbcdcpcD/lBmL9@T590> (raw)
In-Reply-To: <1edfa6a2ffd66d55e6345a477df5387d2c1415d0.1626653825.git.asml.silence@gmail.com>

On Mon, Jul 19, 2021 at 11:53:00AM +0100, 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.
> 
> 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;
> +			}

It is unlikely to happen:

        unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
        struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
        struct page **pages = (struct page **)bv;

		pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
		size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);

>  			__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);

Same with above.

Thanks,
Ming