Re: sound: use-after-free in snd_timer_interrupt

From: Takashi Iwai
Date: Wed Jan 13 2016 - 15:30:24 EST

On Wed, 13 Jan 2016 20:41:30 +0100,
Dmitry Vyukov wrote:
>
> 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:

Is it the result with all patches, i.e. four patches (two for
sequencer and two for timer)?


Takashi

>
> 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
> ==================================================================
>