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@redhat.com Link: https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2262077.html Fixes: 1bdc76aea115 ("iov_iter: use bvec iterator to implement iterate_bvec()") Reported-by: syzbot syzbot+61acc40a49a3e46e25ea@syzkaller.appspotmail.com Tested-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Al Viro viro@zeniv.linux.org.uk Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org

---

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