On Tue, Apr 7, 2020 at 1:00 PM Luis Chamberlain <mcgrof@xxxxxxxxxx> wrote: > > On Tue, Apr 07, 2020 at 10:47:01AM +0800, yukuai (C) wrote: > > On 2020/4/3 16:19, Ming Lei wrote: > > > > > BTW, Yu Kuai posted one patch for this issue, looks that approach > > > is simpler: > > > > > > https://lore.kernel.org/linux-block/20200324132315.22133-1-yukuai3@xxxxxxxxxx/ > > > > > > > > > > I think the issue might not be fixed with the patch seires. > > > > At first, I think there are two key points for the issure: > > 1. The final release of queue is delayed in a workqueue > > 2. The creation of 'q->debugfs_dir' might failed(only if 1 exist) > > And if we can fix any of the above problem, the UAF issue will be fixed. > > (BTW, I did not come up with a good idea for problem 1, and my approach > > is for problem 2.) > > > > The third patch "block: avoid deferral of blk_release_queue() work" is > > not enough to fix problem 1: > > a. if CONFIG_DEBUG_KOBJECT_RELEASE is enable: > > static void kobject_release(struct kref *kref) > > { > > struct kobject *kobj = container_of(kref, struct kobject, kref); > > #ifdef CONFIG_DEBUG_KOBJECT_RELEASE > > unsigned long delay = HZ + HZ * (get_random_int() & 0x3); > > pr_info("kobject: '%s' (%p): %s, parent %p (delayed %ld)\n", > > ┊kobject_name(kobj), kobj, __func__, kobj->parent, delay); > > INIT_DELAYED_WORK(&kobj->release, kobject_delayed_cleanup); > > > > schedule_delayed_work(&kobj->release, delay); > > #else > > kobject_cleanup(kobj); > > #endif > > } > > b. when 'kobject_put' is called from blk_cleanup_queue, can we make sure > > it is the last reference? > > You are right, I think I know the fix for this now. Will run some more > tests. Yeap, we were just not refcounting during blktrace. I'll send a fix as part of the series. Luis
