Re: [RFC v2 10/14] iomap: fix iomap_dio_zero() for fs bs > system page size

Hannes Reinecke
2024-02-13T15:06:22Z

On 2/13/24 10:37, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
>
> iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> size < page_size. This is true for most filesystems at the moment.
>
> If the block size > page size, this will send the contents of the page
> next to zero page(as len > PAGE_SIZE) to the underlying block device,
> causing FS corruption.
>
> iomap is a generic infrastructure and it should not make any assumptions
> about the fs block size and the page size of the system.
>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
> fs/iomap/direct-io.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index bcd3f8cf5ea4..04f6c5548136 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -239,14 +239,23 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
> struct page *page = ZERO_PAGE(0);
> struct bio *bio;
>
> - bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
> + WARN_ON_ONCE(len > (BIO_MAX_VECS * PAGE_SIZE));
> +
> + bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS,
> + REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
> fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
> GFP_KERNEL);
> +
> bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
> bio->bi_private = dio;
> bio->bi_end_io = iomap_dio_bio_end_io;
>
> - __bio_add_page(bio, page, len, 0);
> + while (len) {
> + unsigned int io_len = min_t(unsigned int, len, PAGE_SIZE);
> +
> + __bio_add_page(bio, page, io_len, 0);
> + len -= io_len;
> + }
> iomap_dio_submit_bio(iter, dio, bio, pos);
> }
>
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes