Re: use-after-free in perf_trace_btrfs__work

[Chris Mason]

On Thu, Jan 14, 2016 at 10:07:31PM -0500, Dave Jones wrote:
> I just hit a bunch of instances of this spew..
> This is on Linus' tree from a few hours ago
> 
> ==================================================================
> BUG: KASAN: use-after-free in perf_trace_btrfs__work+0x1b1/0x2a0 [btrfs] at addr ffff8800b7ea2e60
> Read of size 8 by task trinity-c14/6745
> =============================================================================
> BUG kmalloc-256 (Not tainted): kasan: bad access detected
> -----------------------------------------------------------------------------
> 
> Disabling lock debugging due to kernel taint
> INFO: Allocated in btrfs_wq_submit_bio+0xd1/0x300 [btrfs] age=63 cpu=1 pid=6745
> 	___slab_alloc.constprop.70+0x4de/0x580
> 	__slab_alloc.isra.67.constprop.69+0x48/0x80
> 	kmem_cache_alloc_trace+0x24c/0x2e0
> 	btrfs_wq_submit_bio+0xd1/0x300 [btrfs]
> 	btrfs_submit_bio_hook+0x118/0x260 [btrfs]
> 	neigh_sysctl_register+0x201/0x360
> 	devinet_sysctl_register+0x73/0xe0
> 	inetdev_init+0x119/0x1f0
> 	inetdev_event+0x5b3/0x7e0
> 	notifier_call_chain+0x4e/0xd0
> 	raw_notifier_call_chain+0x16/0x20
> 	call_netdevice_notifiers_info+0x3d/0x70
> 	register_netdevice+0x62d/0x730
> 	register_netdev+0x1a/0x30
> 	loopback_net_init+0x5d/0xd0
> 	ops_init+0x5b/0x1e0
> INFO: Freed in run_one_async_free+0x12/0x20 [btrfs] age=177 cpu=1 pid=8018
> 	__slab_free+0x19e/0x2d0
> 	kfree+0x24e/0x270
> 	run_one_async_free+0x12/0x20 [btrfs]
> 	btrfs_scrubparity_helper+0x38d/0x740 [btrfs]
> 	btrfs_worker_helper+0xe/0x10 [btrfs]
> 	process_one_work+0x417/0xa40
> 	worker_thread+0x8b/0x730
> 	kthread+0x199/0x1c0
> 	ret_from_fork+0x3f/0x70
> INFO: Slab 0xffffea0002dfa800 objects=28 used=28 fp=0x          (null) flags=0x4000000000004080
> INFO: Object 0xffff8800b7ea2da0 @offset=11680 fp=0xffff8800b7ea2480

static inline void __btrfs_queue_work(struct __btrfs_workqueue *wq,
                                      struct btrfs_work *work)
{
        unsigned long flags;
	
        work->wq = wq;
        thresh_queue_hook(wq);
        if (work->ordered_func) {
                spin_lock_irqsave(&wq->list_lock, flags);
                list_add_tail(&work->ordered_list, &wq->ordered_list);
                spin_unlock_irqrestore(&wq->list_lock, flags);
        }
        queue_work(wq->normal_wq, &work->normal_work);
        trace_btrfs_work_queued(work);
}

Qu, 'work' can be freed before queue_work returns.  I don't see any reason
here to have it after the queue_work() call, do you?

-chris