On 09/06/2021 07:30, Ming Lei wrote:
Thanks for the fix
tagset can't be used after blk_cleanup_queue() is returned because
freeing tagset usually follows blk_clenup_queue(). Commit d97e594c5166
("blk-mq: Use request queue-wide tags for tagset-wide sbitmap") adds
check on q->tag_set->flags in blk_mq_exit_sched(), and causes
use-after-free.
Fixes it by using hctx->flags.
The tagset is a member of the Scsi_Host structure. So it is true that
this memory may be freed before the request_queue is exited?
Reported-by: syzbot+77ba3d171a25c56756ea@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d97e594c5166 ("blk-mq: Use request queue-wide tags for tagset-wide sbitmap")
Cc: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-mq-sched.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index a9182d2f8ad3..80273245d11a 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -680,6 +680,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
{
struct blk_mq_hw_ctx *hctx;
unsigned int i;
+ unsigned int flags = 0;
queue_for_each_hw_ctx(q, hctx, i) {
blk_mq_debugfs_unregister_sched_hctx(hctx);
@@ -687,12 +688,13 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
e->type->ops.exit_hctx(hctx, i);
hctx->sched_data = NULL;
}
+ flags = hctx->flags;
I know the choice is limited, but it is unfortunate that we must set
flags in a loop
}
blk_mq_debugfs_unregister_sched(q);
if (e->type->ops.exit_sched)
e->type->ops.exit_sched(e);
blk_mq_sched_tags_teardown(q);
- if (blk_mq_is_sbitmap_shared(q->tag_set->flags))
+ if (blk_mq_is_sbitmap_shared(flags))
blk_mq_exit_sched_shared_sbitmap(q);
this is
blk_mq_exit_sched_shared_sbitmap(struct request_queue *queue)
{
sbitmap_queue_free(&queue->sched_bitmap_tags);
..
}
And isn't it safe to call sbitmap_queue_free() when
sbitmap_queue_init_node() has not been called?
I'm just wondering if we can always call
blk_mq_exit_sched_shared_sbitmap()? I know it's not an ideal choice either.
Thanks,
John
q->elevator = NULL;
}
