Bios queued into BFQ IO scheduler can be associated with a cgroup that was already offlined. This may then cause insertion of this bfq_group into a service tree. But this bfq_group will get freed as soon as last bio associated with it is completed leading to use after free issues for service tree users. Fix the problem by making sure we always operate on online bfq_group. If the bfq_group associated with the bio is not online, we pick the first online parent.

CC: stable@vger.kernel.org Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support") Signed-off-by: Jan Kara jack@suse.cz --- block/bfq-cgroup.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c index 32d2c2a47480..09574af83566 100644 --- a/block/bfq-cgroup.c +++ b/block/bfq-cgroup.c @@ -612,10 +612,19 @@ static void bfq_link_bfqg(struct bfq_data *bfqd, struct bfq_group *bfqg) struct bfq_group *bfq_bio_bfqg(struct bfq_data *bfqd, struct bio *bio) { struct blkcg_gq *blkg = bio->bi_blkg; + struct bfq_group *bfqg;

- if (!blkg) - return bfqd->root_group; - return blkg_to_bfqg(blkg); + while (blkg) { + bfqg = blkg_to_bfqg(blkg); + if (bfqg->online) { + bio_associate_blkg_from_css(bio, &blkg->blkcg->css); + return bfqg; + } + blkg = blkg->parent; + } + bio_associate_blkg_from_css(bio, + &bfqg_to_blkg(bfqd->root_group)->blkcg->css); + return bfqd->root_group; }

/**