Re: [PATCH V7 0/4] blk-mq: fix request UAF related with iterating over tagset requests

["yukuai (C)" <yukuai3@huawei.com>]

On 2021/05/11 23:22, Ming Lei wrote:
> Hi Jens,
> 
> This patchset fixes the request UAF issue by one simple approach,
> without clearing ->rqs[] in fast path, please consider it for 5.13.
> 
> 1) grab request's ref before calling ->fn in blk_mq_tagset_busy_iter,
> and release it after calling ->fn, so ->fn won't be called for one
> request if its queue is frozen, done in 2st patch
> 
> 2) clearing any stale request referred in ->rqs[] before freeing the
> request pool, one per-tags spinlock is added for protecting
> grabbing request ref vs. clearing ->rqs[tag], so UAF by refcount_inc_not_zero
> in bt_tags_iter() is avoided, done in 3rd patch.
> 
> V7:
> 	- fix one null-ptr-deref during updating nr_hw_queues, because
> 	blk_mq_clear_flush_rq_mapping() may touch non-mapped hw queue's
> 	tags, only patch 4/4 is modified, reported and verified by
> 	Shinichiro Kawasaki
> 	- run blktests and not see regression
> 
> V6:
> 	- hold spin lock when reading rq via ->rq[tag_bit], the issue is
> 	  added in V5
> 	- make blk_mq_find_and_get_req() more clean, as suggested by Bart
> 	- not hold tags->lock when clearing ->rqs[] for avoiding to disable
> 	interrupt a bit long, as suggested by Bart
> 	- code style change, as suggested by Christoph
> 
> V5:
> 	- cover bt_iter() by same approach taken in bt_tags_iter(), and pass
> 	John's invasive test
> 	- add tested-by/reviewed-by tag
> 
> V4:
> 	- remove hctx->fq-flush_rq from tags->rqs[] before freeing hw queue,
> 	patch 4/4 is added, which is based on David's patch.
> 
> V3:
> 	- drop patches for completing requests started in iterator ->fn,
> 	  because blk-mq guarantees that valid request is passed to ->fn,
> 	  and it is driver's responsibility for avoiding double completion.
> 	  And drivers works well for not completing rq twice.
> 	- add one patch for avoiding double accounting of flush rq
> 
> V2:
> 	- take Bart's suggestion to not add blk-mq helper for completing
> 	  requests when it is being iterated
> 	- don't grab rq->ref if the iterator is over static rqs because
> 	the use case do require to iterate over all requests no matter if
> 	the request is initialized or not
> 
> 
> Ming Lei (4):
>    block: avoid double io accounting for flush request
>    blk-mq: grab rq->refcount before calling ->fn in
>      blk_mq_tagset_busy_iter
>    blk-mq: clear stale request in tags->rq[] before freeing one request
>      pool
>    blk-mq: clearing flush request reference in tags->rqs[]
> 
>   block/blk-flush.c  |  3 +-
>   block/blk-mq-tag.c | 49 ++++++++++++++++++------
>   block/blk-mq-tag.h |  6 +++
>   block/blk-mq.c     | 95 ++++++++++++++++++++++++++++++++++++++++------
>   block/blk-mq.h     |  1 +
>   5 files changed, 130 insertions(+), 24 deletions(-)
> 

Hi, ming

I see this patchset was applied to fix the problem while iterating over
tagset, however blk_mq_tag_to_rq() is still untouched, and this
interface might still return freed request.

Any reason why this interface didn't use the same solution ?
(hold tags->lock and return null if ref is 0)

Thanks
Kuai