Commit 7bed6f3d authored Jan 16, 2024 by Matthew Wilcox (Oracle) Committed by Jens Axboe Jan 16, 2024

block: Fix iterating over an empty bio with bio_for_each_folio_all



If the bio contains no data, bio_first_folio() calls page_folio() on a
NULL pointer and oopses.  Move the test that we've reached the end of
the bio from bio_next_folio() to bio_first_folio().

Reported-by:  <syzbot+8b23309d5788a79d3eea@syzkaller.appspotmail.com>
Reported-by:  <syzbot+004c1e0fced2b4bc3dcc@syzkaller.appspotmail.com>
Fixes: 640d1930 ("block: Add bio_for_each_folio_all()")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240116212959.3413014-1-willy@infradead.org


[axboe: add unlikely() to error case]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent be50df31

include/linux/bio.h

+6 −3

Original line number	Diff line number	Diff line
		@@ -286,6 +286,11 @@ static inline void bio_first_folio(struct folio_iter fi, struct bio bio,
		{
		struct bio_vec *bvec = bio_first_bvec_all(bio) + i;

		if (unlikely(i >= bio->bi_vcnt)) {
		fi->folio = NULL;
		return;
		}

		fi->folio = page_folio(bvec->bv_page);
		fi->offset = bvec->bv_offset +
		PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
		@@ -303,10 +308,8 @@ static inline void bio_next_folio(struct folio_iter fi, struct bio bio)
		fi->offset = 0;
		fi->length = min(folio_size(fi->folio), fi->_seg_count);
		fi->_next = folio_next(fi->folio);
		} else if (fi->_i + 1 < bio->bi_vcnt) {
		bio_first_folio(fi, bio, fi->_i + 1);
		} else {
		fi->folio = NULL;
		bio_first_folio(fi, bio, fi->_i + 1);
		}
		}