| Message ID | 20240116212959.3413014-1-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: Fix iterating over an empty bio with bio_for_each_folio_all | expand |
On Tue, 16 Jan 2024 21:29:59 +0000, Matthew Wilcox (Oracle) wrote: > 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(). > > Applied, thanks! [1/1] block: Fix iterating over an empty bio with bio_for_each_folio_all commit: 7bed6f3d08b7af27b7015da8dc3acf2b9c1f21d7 Best regards,
On Tue, Jan 16, 2024 at 03:03:46PM -0700, Jens Axboe wrote: > > On Tue, 16 Jan 2024 21:29:59 +0000, Matthew Wilcox (Oracle) wrote: > > 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(). > > > > > > Applied, thanks! > > [1/1] block: Fix iterating over an empty bio with bio_for_each_folio_all > commit: 7bed6f3d08b7af27b7015da8dc3acf2b9c1f21d7 I see you added an unlikely(), and I'm not sure it's justified. It's going to be true at the end of each iteration. For a bio that contains one bio_vec, it will be false once and true once. It'd be like writing a for loop as: for (i = 0; likely(i < n); i++) { } which I've never seen us do. I don't know that it's worth taking out, but I wouldn't've put it in. I wouldn't be surprised to see benchmarks show it's a bad idea. Could you at least _say_ when you're going to make that kind of change? I wouldn't've noticed except that I got a merge conflict.
diff --git a/include/linux/bio.h b/include/linux/bio.h index ec4db73e5f4e..1518f1201ddd 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -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 (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); } }
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: 640d1930bef4 ("block: Add bio_for_each_folio_all()") Cc: stable@vger.kernel.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- include/linux/bio.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)