[PATCH 5.17 630/772] bfq: Update cgroup information before merging bio

Greg Kroah-Hartman
2022-06-07T21:37:42Z

From: Jan Kara <jack@suse.cz>

commit ea591cd4eb270393810e7be01feb8fde6a34fbbe upstream.

When the process is migrated to a different cgroup (or in case of
writeback just starts submitting bios associated with a different
cgroup) bfq_merge_bio() can operate with stale cgroup information in
bic. Thus the bio can be merged to a request from a different cgroup or
it can result in merging of bfqqs for different cgroups or bfqqs of
already dead cgroups and causing possible use-after-free issues. Fix the
problem by updating cgroup information in bfq_merge_bio().

CC: stable@vger.kernel.org
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Tested-by: "yukuai (C)" <yukuai3@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220401102752.8599-4-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
block/bfq-iosched.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2461,10 +2461,17 @@ static bool bfq_bio_merge(struct request

spin_lock_irq(&bfqd->lock);

- if (bic)
+ if (bic) {
+ /*
+ * Make sure cgroup info is uptodate for current process before
+ * considering the merge.
+ */
+ bfq_bic_update_cgroup(bic, bio);
+
bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
- else
+ } else {
bfqd->bio_bfqq = NULL;
+ }
bfqd->bio_bic = bic;

ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);