Re: sound: use-after-free in snd_timer_interrupt

From: Dmitry Vyukov
Date: Wed Jan 13 2016 - 14:42:03 EST

On Wed, Jan 13, 2016 at 8:30 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> On Wed, Jan 13, 2016 at 8:05 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
>> On Wed, 13 Jan 2016 19:34:36 +0100,
>> Dmitry Vyukov wrote:
>>>
>>> On Wed, Jan 13, 2016 at 5:53 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
>>> > This and your other relevant reports seem pointing the race of timer
>>> > ioctls. Although snd_timer_close() itself calls snd_timer_stop(),
>>> > there is no other protection against the concurrent execution.
>>> >
>>> > If my guess is correct, a simplistic fix like below should work. It
>>> > basically serializes the timer ioctl by using a new mutex (and
>>> > replacing the old tread_sem mutex). They are no longtime blocking
>>> > calls, so this shouldn't be a big problem. But certainly there can be
>>> > a less intrusive way to paper over this if this really matters.
>>> >
>>> > In this case for timer.c, I'd leave the final decision rather to
>>> > Jaroslav. Jaroslav, what do you think?
>>>
>>>
>>> After applying this patch I still see the following WARNINGS:
>>>
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 2 PID: 30398 at lib/list_debug.c:53 __list_del_entry+0x10b/0x1e0()
>>> list_del corruption, ffff880032d933b0->next is LIST_POISON1 (dead000000000100)
>>> Modules linked in:
>>> CPU: 2 PID: 30398 Comm: syz-executor Not tainted 4.4.0+ #241
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>> 00000000ffffffff ffff8800627778d8 ffffffff82926eed ffff880062777948
>>> ffff880061c2af80 ffffffff8660b640 ffff880062777918 ffffffff81350c89
>>> ffffffff8298e77b ffffed000c4eef25 ffffffff8660b640 0000000000000035
>>> Call Trace:
>>> [< inline >] __dump_stack lib/dump_stack.c:15
>>> [<ffffffff82926eed>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>>> [<ffffffff81350c89>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:483
>>> [<ffffffff81350d99>] warn_slowpath_fmt+0xa9/0xd0 kernel/panic.c:495
>>> [<ffffffff8298e77b>] __list_del_entry+0x10b/0x1e0 lib/list_debug.c:51
>>> [< inline >] list_del_init include/linux/list.h:145
>>> [<ffffffff84ebd199>] _snd_timer_stop+0x119/0x450 sound/core/timer.c:501
>>
>> This is
>>
>> list_del_init(&timeri->active_list);
>>
>> right? Possibly the following oneliner covers it?
>
> Yes, that is this line.
> Yes, these two patches fix use-after-frees and GPFs.
>
> Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>


I've re-tested the programs that I reported. But when I started the
fuzzer again I hit a similar use-after-free in snd_timer_interrupt:

BUG: KASAN: use-after-free in snd_timer_interrupt+0xaea/0xc40 at addr
ffff8800644df960
Read of size 8 by task kworker/u10:3/561
=============================================================================
BUG kmalloc-256 (Not tainted): kasan: bad access detected
-----------------------------------------------------------------------------

INFO: Allocated in snd_timer_instance_new+0x52/0x3a0 age=13 cpu=2 pid=18656
[< none >] ___slab_alloc+0x486/0x4e0 mm/slub.c:2468
[< none >] __slab_alloc+0x66/0xc0 mm/slub.c:2497
[< inline >] slab_alloc_node mm/slub.c:2560
[< inline >] slab_alloc mm/slub.c:2602
[< none >] kmem_cache_alloc_trace+0x284/0x310 mm/slub.c:2619
[< inline >] kmalloc include/linux/slab.h:458
[< inline >] kzalloc include/linux/slab.h:602
[< none >] snd_timer_instance_new+0x52/0x3a0 sound/core/timer.c:105
[< none >] snd_timer_open+0x522/0xc90 sound/core/timer.c:286
[< none >] snd_seq_timer_open+0x223/0x540
sound/core/seq/seq_timer.c:279
[< none >] snd_seq_queue_use+0x147/0x230
sound/core/seq/seq_queue.c:528
[< none >] snd_seq_queue_alloc+0x36a/0x4d0
sound/core/seq/seq_queue.c:199
[< none >] snd_seq_ioctl_create_queue+0xdb/0x2b0
sound/core/seq/seq_clientmgr.c:1536
[< none >] snd_seq_do_ioctl+0x19a/0x1c0
sound/core/seq/seq_clientmgr.c:2209
[< none >] snd_seq_ioctl+0x5d/0x80 sound/core/seq/seq_clientmgr.c:2224
[< inline >] vfs_ioctl fs/ioctl.c:43
[< none >] do_vfs_ioctl+0x18c/0xfa0 fs/ioctl.c:674
[< inline >] SYSC_ioctl fs/ioctl.c:689
[< none >] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680
[< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185

INFO: Freed in snd_timer_close+0x354/0x5f0 age=13 cpu=3 pid=18658
[< none >] __slab_free+0x1fc/0x320 mm/slub.c:2678
[< inline >] slab_free mm/slub.c:2833
[< none >] kfree+0x2a8/0x2d0 mm/slub.c:3662
[< none >] snd_timer_close+0x354/0x5f0 sound/core/timer.c:364
[< none >] snd_seq_timer_close+0x9e/0x100
sound/core/seq/seq_timer.c:312
snd_seq_queue_timer
[< none >] snd_seq_ioctl_set_queue_timer+0x159/0x300
sound/core/seq/seq_clientmgr.c:1809
[< none >] snd_seq_do_ioctl+0x19a/0x1c0
sound/core/seq/seq_clientmgr.c:2209
[< none >] snd_seq_ioctl+0x5d/0x80 sound/core/seq/seq_clientmgr.c:2224
[< inline >] vfs_ioctl fs/ioctl.c:43
[< none >] do_vfs_ioctl+0x18c/0xfa0 fs/ioctl.c:674
[< inline >] SYSC_ioctl fs/ioctl.c:689
[< none >] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680
[< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185

INFO: Slab 0xffffea0001913700 objects=22 used=10 fp=0xffff8800644df8e0
flags=0x5fffc0000004080
INFO: Object 0xffff8800644df8e0 @offset=14560 fp=0xffff8800644ddf48
CPU: 2 PID: 561 Comm: kworker/u10:3 Tainted: G B 4.4.0+ #243
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: events_unbound call_usermodehelper_exec_work
00000000ffffffff ffff88006d607be0 ffffffff82926eed ffff88003e807000
ffff8800644df8e0 ffff8800644dc000 ffff88006d607c10 ffffffff81740ca4
ffff88003e807000 ffffea0001913700 ffff8800644df8e0 ffff8800644df960

Call Trace:
[< inline >] kasan_report mm/kasan/report.c:274
[<ffffffff8174a1fe>] __asan_report_load8_noabort+0x3e/0x40
mm/kasan/report.c:295
[<ffffffff84ebe84a>] snd_timer_interrupt+0xaea/0xc40 sound/core/timer.c:680
[<ffffffff84ec6c16>] snd_hrtimer_callback+0x166/0x230 sound/core/hrtimer.c:54
[< inline >] __run_hrtimer kernel/time/hrtimer.c:1229
[<ffffffff814c3723>] __hrtimer_run_queues+0x363/0xc10
kernel/time/hrtimer.c:1293
[<ffffffff814c5732>] hrtimer_interrupt+0x182/0x430 kernel/time/hrtimer.c:1327
[<ffffffff8124e10f>] local_apic_timer_interrupt+0x6f/0xe0
arch/x86/kernel/apic/apic.c:907
[<ffffffff81251576>] smp_apic_timer_interrupt+0x76/0xa0
arch/x86/kernel/apic/apic.c:931
[<ffffffff86273eec>] apic_timer_interrupt+0x8c/0xa0
arch/x86/entry/entry_64.S:520
<EOI> [< inline >] alloc_task_struct_node kernel/fork.c:142
<EOI> [< inline >] dup_task_struct kernel/fork.c:342
<EOI> [<ffffffff8134950e>] copy_process.part.35+0x22e/0x5770
kernel/fork.c:1304
[< inline >] slab_alloc_node mm/slub.c:2560
[<ffffffff817447f3>] kmem_cache_alloc_node+0x93/0x300 mm/slub.c:2630
[< inline >] alloc_task_struct_node kernel/fork.c:142
[< inline >] dup_task_struct kernel/fork.c:342
[<ffffffff8134950e>] copy_process.part.35+0x22e/0x5770 kernel/fork.c:1304
[< inline >] copy_process kernel/fork.c:1275
[<ffffffff8134ed7c>] _do_fork+0x1bc/0xcb0 kernel/fork.c:1724
[<ffffffff8134f8a4>] kernel_thread+0x34/0x40 kernel/fork.c:1785
[< inline >] call_usermodehelper_exec_sync kernel/kmod.c:275
[<ffffffff81391874>] call_usermodehelper_exec_work+0xf4/0x230 kernel/kmod.c:327
[<ffffffff8139e824>] process_one_work+0x794/0x1440 kernel/workqueue.c:2036
[<ffffffff8139f5ab>] worker_thread+0xdb/0xfc0 kernel/workqueue.c:2170
[<ffffffff813b2cef>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
[<ffffffff862734af>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
==================================================================