Re: use-after-free in perf_trace_btrfs__work

[Qu Wenruo]

Chris Mason wrote on 2016/01/21 12:06 -0500:

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

Right, trace_btrfs_work_queued() should be called at the very beginning.

I'll submit the fix soon.

Thanks,
Qu