On Fri, Aug 06, 2021 at 11:40:25AM +0800, yukuai (C) wrote: > 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) It is driver's responsibility to cover race between normal completion and timeout/error handing, so driver has the knowledge if one tag is valid or not. In short, it is driver's responsibility to guarantee that valid 'tag' is passed to blk_mq_tag_to_rq(). Thanks, Ming
