On Mon, Aug 17, 2020 at 06:00:55PM +0800, Ming Lei wrote:
> Block layer usually doesn't support or allow zero-length bvec. Since
> commit 1bdc76aea115 ("iov_iter: use bvec iterator to implement
> iterate_bvec()"), iterate_bvec() switches to bvec iterator. However,
> Al mentioned that 'Zero-length segments are not disallowed' in iov_iter.
>
> Fixes for_each_bvec() so that it can move on after seeing one zero
> length bvec.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> Link: https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg2262077.html
> Fixes: 1bdc76aea115 ("iov_iter: use bvec iterator to implement iterate_bvec()")
> Reported-by: syzbot <syzbot+61acc40a49a3e46e25ea@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Tested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
> V2:
> - fix reported-by tag
>
> include/linux/bvec.h | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> index ac0c7299d5b8..9c4fab5f22a7 100644
> --- a/include/linux/bvec.h
> +++ b/include/linux/bvec.h
> @@ -117,11 +117,18 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
> return true;
> }
>
> +static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
> +{
> + iter->bi_bvec_done = 0;
> + iter->bi_idx++;
> +}
> +
> #define for_each_bvec(bvl, bio_vec, iter, start) \
> for (iter = (start); \
> (iter).bi_size && \
> ((bvl = bvec_iter_bvec((bio_vec), (iter))), 1); \
> - bvec_iter_advance((bio_vec), &(iter), (bvl).bv_len))
> + (bvl).bv_len ? bvec_iter_advance((bio_vec), &(iter), \
> + (bvl).bv_len) : bvec_iter_skip_zero_bvec(&(iter)))
>
> /* for iterating one bio from start to end */
> #define BVEC_ITER_ALL_INIT (struct bvec_iter) \
> --
> 2.25.2
>
Hello Jens,
Looks at least two reports can be fixed by this patch, so could you
take a look?
Thanks,
Ming
