On Tue, Apr 18 2023 at 11:20P -0400, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Mon, Apr 17 2023 at 3:11P -0400, > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > If we use bio_for_each_folio_all on an empty bio, it will access the first > > bio vector unconditionally (it is uninitialized) and it may crash > > depending on the uninitialized data. > > > > This patch fixes it by checking the parameter "i" against "bio->bi_vcnt" > > and returning NULL fi->folio if it is out of range. > > > > The patch also drops the test "if (fi->_i + 1 < bio->bi_vcnt)" from > > bio_next_folio because the same condition is already being checked in > > bio_first_folio. > > > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > This fix is a prereq for this dm-crypt patch to use folios: > https://patchwork.kernel.org/project/dm-devel/patch/alpine.LRH.2.21.2302161619430.5436@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > Mikulas explained why an empty bio is possible here: > https://listman.redhat.com/archives/dm-devel/2023-April/053916.html > > Reviewed-by: Mike Snitzer <snitzer@xxxxxxxxxx> Hey Jens (and Matthew), Can you please pick this up? Without it DM needs to do the checking (by open-coding a fixed variant of bio_for_each_folio_all); while we _could_ do that: fixing bio_first_folio seems best. Thanks, Mike
