Hello Shinichiro, Thanks for your test! On Tue, May 11, 2021 at 05:05:52AM +0000, Shinichiro Kawasaki wrote: > On May 07, 2021 / 22:42, 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. > > Ming, thank you for your effort to fix the UAF issue. I applied the V6 series to > the kernel v5.13-rc1, and confirmed that the series avoids the UAF I had been > observing with blktests block/005 and HDD behind HBA. This is good. However, I > found that the series triggered block/029 hang. Let me share the kernel message > below, which was printed at the hang. KASAN reported null-ptr-deref. > > [ 2124.489023] run blktests block/029 at 2021-05-11 13:42:22 > [ 2124.561386] null_blk: module loaded > [ 2125.201166] general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] SMP KASAN PTI > [ 2125.212387] KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097] It is because this hw queue isn't mapped yet and new added hw queue is mapped in blk_mq_map_swqueue(), and the following change can fix it, and I will post V7 after careful test. diff --git a/block/blk-mq.c b/block/blk-mq.c index fcd5ed79011f..691b555c26fa 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2652,6 +2652,10 @@ static void blk_mq_clear_flush_rq_mapping(struct blk_mq_tags *tags, int i; unsigned long flags; + /* return if hw queue isn't mapped */ + if (!tags) + return; + WARN_ON_ONCE(refcount_read(&flush_rq->ref) != 0); for (i = 0; i < queue_depth; i++) Thanks, Ming
