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. Luis
