Re: sound: use-after-free in snd_timer_interrupt

From: Takashi Iwai
Date: Sun Apr 03 2016 - 02:34:42 EST

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On Sun, 03 Apr 2016 08:06:09 +0200,
Dmitry Vyukov wrote:
>
> On Sat, Apr 2, 2016 at 6:30 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> > On Sat, 02 Apr 2016 11:08:40 +0200,
> > Dmitry Vyukov wrote:
> >>
> >> Hello,
> >>
> >> I am hitting the following use-after-free while running syzkaller
> >> fuzzer on commit 8e0f93cda48ed054e1216bab5c60017e1a5fc1e8
> >>
> >> ==================================================================
> >> BUG: KASAN: use-after-free in __list_del_entry+0x1d3/0x1e0 at addr
> >> ffff88002ebf6e20
> >> Read of size 8 by task syz-executor/7684
> >> =============================================================================
> >> BUG kmalloc-256 (Not tainted): kasan: bad access detected
> >> -----------------------------------------------------------------------------
> >>
> >> INFO: Allocated in snd_timer_instance_new+0x52/0x3a0 age=5 cpu=0 pid=7693
> >> [< none >] ___slab_alloc+0x578/0x5d0 mm/slub.c:2464
> >> [< none >] __slab_alloc+0x66/0xc0 mm/slub.c:2493
> >> [< inline >] slab_alloc_node mm/slub.c:2556
> >> [< inline >] slab_alloc mm/slub.c:2598
> >> [< none >] kmem_cache_alloc_trace+0x242/0x3b0 mm/slub.c:2615
> >> [< inline >] kmalloc include/linux/slab.h:463
> >> [< inline >] kzalloc include/linux/slab.h:607
> >> [< none >] snd_timer_instance_new+0x52/0x3a0 sound/core/timer.c:106
> >> [< none >] snd_timer_open+0x522/0xd20 sound/core/timer.c:289
> >> [< inline >] snd_timer_user_tselect sound/core/timer.c:1612
> >> [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1888
> >> [< none >] snd_timer_user_ioctl+0x8f4/0x2490 sound/core/timer.c:1918
> >> [< inline >] vfs_ioctl fs/ioctl.c:43
> >> [< none >] do_vfs_ioctl+0x18c/0xfb0 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+0x3ee/0x750 age=9 cpu=0 pid=7693
> >> [< none >] __slab_free+0x1fc/0x320 mm/slub.c:2674
> >> [< inline >] slab_free mm/slub.c:2829
> >> [< none >] kfree+0x2f5/0x370 mm/slub.c:3660
> >> [< none >] snd_timer_close+0x3ee/0x750 sound/core/timer.c:375
> >> [< inline >] snd_timer_user_tselect sound/core/timer.c:1602
> >> [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1888
> >> [< none >] snd_timer_user_ioctl+0x7cd/0x2490 sound/core/timer.c:1918
> >> [< inline >] vfs_ioctl fs/ioctl.c:43
> >> [< none >] do_vfs_ioctl+0x18c/0xfb0 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 0xffffea0000bafd00 objects=22 used=11 fp=0xffff88002ebf6d80
> >> flags=0x1fffc0000004080
> >> INFO: Object 0xffff88002ebf6d80 @offset=11648 fp=0xffff88002ebf5110
> >> CPU: 3 PID: 7684 Comm: syz-executor Tainted: G B 4.5.0-rc7+ #337
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >> ffffffff87b7d480 ffff88006d707bb0 ffffffff82c2125f ffffffff00bafd00
> >> fffffbfff0f6fa90 ffff88003e807000 ffff88002ebf6d80 ffff88002ebf4000
> >> ffffea0000bafd00 ffff88002ebf6e18 ffff88006d707be0 ffffffff8176dcc4
> >>
> >> Call Trace:
> >> [<ffffffff81777e4e>] __asan_report_load8_noabort+0x3e/0x40
> >> mm/kasan/report.c:295
> >> [<ffffffff82c88f63>] __list_del_entry+0x1d3/0x1e0 lib/list_debug.c:48
> >> [< inline >] list_del_init include/linux/list.h:145
> >> [<ffffffff852942f9>] snd_timer_interrupt+0x5b9/0xc80 sound/core/timer.c:791
> >> [<ffffffff8529acc9>] snd_hrtimer_callback+0x169/0x230 sound/core/hrtimer.c:54
> >> [< inline >] __run_hrtimer kernel/time/hrtimer.c:1248
> >> [<ffffffff814c3911>] __hrtimer_run_queues+0x331/0xe90
> >> kernel/time/hrtimer.c:1312
> >> [<ffffffff814c62e2>] hrtimer_interrupt+0x182/0x430 kernel/time/hrtimer.c:1346
> >> [<ffffffff81255ec2>] local_apic_timer_interrupt+0x72/0xe0
> >> arch/x86/kernel/apic/apic.c:907
> >> [<ffffffff812593e9>] smp_apic_timer_interrupt+0x79/0xa0
> >> arch/x86/kernel/apic/apic.c:931
> >> [<ffffffff866d256c>] apic_timer_interrupt+0x8c/0xa0
> >> arch/x86/entry/entry_64.S:520
> >> [< inline >] spin_unlock_irqrestore include/linux/spinlock.h:362
> >> [<ffffffff8177369e>] __slab_free+0x1ae/0x320 mm/slub.c:2681
> >> [< inline >] slab_free mm/slub.c:2829
> >> [<ffffffff81773ed8>] kmem_cache_free+0x318/0x440 mm/slub.c:2838
> >> [<ffffffff81704cb8>] ptlock_free+0x38/0x50 mm/memory.c:3912
> >> [< inline >] pgtable_pmd_page_dtor include/linux/mm.h:1702
> >> [<ffffffff812951ca>] ___pmd_free_tlb+0xaa/0x110 arch/x86/mm/pgtable.c:74
> >> [< inline >] __pmd_free_tlb ./arch/x86/include/asm/pgalloc.h:106
> >> [< inline >] free_pmd_range mm/memory.c:432
> >> [< inline >] free_pud_range mm/memory.c:450
> >> [<ffffffff816f4dc3>] free_pgd_range+0x973/0xbe0 mm/memory.c:526
> >> [<ffffffff816f52f5>] free_pgtables+0x2c5/0x3b0 mm/memory.c:558
> >> [<ffffffff817137c3>] exit_mmap+0x233/0x410 mm/mmap.c:2868
> >> [<ffffffff813543f5>] mmput+0x95/0x230 kernel/fork.c:706
> >> [< inline >] exit_mm kernel/exit.c:436
> >> [<ffffffff81366eb2>] do_exit+0x7b2/0x2d00 kernel/exit.c:735
> >> [<ffffffff81369578>] do_group_exit+0x108/0x330 kernel/exit.c:878
> >> [<ffffffff8138cf14>] get_signal+0x634/0x15e0 kernel/signal.c:2307
> >> [<ffffffff811a7db3>] do_signal+0x83/0x1c90 arch/x86/kernel/signal.c:712
> >> [<ffffffff81006685>] exit_to_usermode_loop+0x1a5/0x210
> >> arch/x86/entry/common.c:247
> >> [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282
> >> [<ffffffff8100866a>] syscall_return_slowpath+0x2ba/0x340
> >> arch/x86/entry/common.c:344
> >> [<ffffffff866d18e2>] int_ret_from_sys_call+0x25/0x9f
> >> arch/x86/entry/entry_64.S:281
> >>
> >> ==================================================================
> >> kasan: GPF could be caused by NULL-ptr deref or user memory
> >> accessgeneral protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
> >> Modules linked in:
> >> CPU: 3 PID: 7684 Comm: syz-executor Tainted: G B 4.5.0-rc7+ #337
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >> task: ffff880061062f80 ti: ffff88005ee10000 task.ti: ffff88005ee10000
> >> RIP: 0010:[<ffffffff82c88e16>] [<ffffffff82c88e16>] __list_del_entry+0x86/0x1e0
> >> RSP: 0018:ffff88006d707cd0 EFLAGS: 00010046
> >> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff88002ebf6e18
> >> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> >> RBP: ffff88006d707cf0 R08: ffffffff89cbcf00 R09: 0000000000000000
> >> R10: ffffed000dae0f8c R11: 0000000000000000 R12: ffff88005ee0d120
> >> R13: ffff8800670a2298 R14: ffff88005ee0d110 R15: ffff88002ebf6e18
> >> FS: 0000000000000000(0000) GS:ffff88006d700000(0000) knlGS:0000000000000000
> >> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> >> CR2: 00000000006e0000 CR3: 0000000007ae9000 CR4: 00000000000006e0
> >> Stack:
> >> ffff88006d707cf0 ffff88002ebf6e18 dffffc0000000000 ffff88005ee0d120
> >> ffff88006d707db0 ffffffff852942f9 ffff8800670a2368 0000000000000082
> >> dffffc0000000000 ffff8800670a234c ffffffff87b7d480 ffffed000ce1446d
> >> Call Trace:
> >> <IRQ>
> >> [< inline >] list_del_init include/linux/list.h:145
> >> [<ffffffff852942f9>] snd_timer_interrupt+0x5b9/0xc80 sound/core/timer.c:791
> >> [<ffffffff8529acc9>] snd_hrtimer_callback+0x169/0x230 sound/core/hrtimer.c:54
> >> [< inline >] __run_hrtimer kernel/time/hrtimer.c:1248
> >> [<ffffffff814c3911>] __hrtimer_run_queues+0x331/0xe90
> >> kernel/time/hrtimer.c:1312
> >> [<ffffffff814c62e2>] hrtimer_interrupt+0x182/0x430 kernel/time/hrtimer.c:1346
> >> [<ffffffff81255ec2>] local_apic_timer_interrupt+0x72/0xe0
> >> arch/x86/kernel/apic/apic.c:907
> >> [<ffffffff812593e9>] smp_apic_timer_interrupt+0x79/0xa0
> >> arch/x86/kernel/apic/apic.c:931
> >> [<ffffffff866d256c>] apic_timer_interrupt+0x8c/0xa0
> >> arch/x86/entry/entry_64.S:520
> >> <EOI>
> >> [< inline >] spin_unlock_irqrestore include/linux/spinlock.h:362
> >> [<ffffffff8177369e>] __slab_free+0x1ae/0x320 mm/slub.c:2681
> >> [< inline >] slab_free mm/slub.c:2829
> >> [<ffffffff81773ed8>] kmem_cache_free+0x318/0x440 mm/slub.c:2838
> >> [<ffffffff81704cb8>] ptlock_free+0x38/0x50 mm/memory.c:3912
> >> [< inline >] pgtable_pmd_page_dtor include/linux/mm.h:1702
> >> [<ffffffff812951ca>] ___pmd_free_tlb+0xaa/0x110 arch/x86/mm/pgtable.c:74
> >> [< inline >] __pmd_free_tlb ./arch/x86/include/asm/pgalloc.h:106
> >> [< inline >] free_pmd_range mm/memory.c:432
> >> [< inline >] free_pud_range mm/memory.c:450
> >> [<ffffffff816f4dc3>] free_pgd_range+0x973/0xbe0 mm/memory.c:526
> >> [<ffffffff816f52f5>] free_pgtables+0x2c5/0x3b0 mm/memory.c:558
> >> [<ffffffff817137c3>] exit_mmap+0x233/0x410 mm/mmap.c:2868
> >> [<ffffffff813543f5>] mmput+0x95/0x230 kernel/fork.c:706
> >> [< inline >] exit_mm kernel/exit.c:436
> >> [<ffffffff81366eb2>] do_exit+0x7b2/0x2d00 kernel/exit.c:735
> >> [<ffffffff81369578>] do_group_exit+0x108/0x330 kernel/exit.c:878
> >> [<ffffffff8138cf14>] get_signal+0x634/0x15e0 kernel/signal.c:2307
> >> [<ffffffff811a7db3>] do_signal+0x83/0x1c90 arch/x86/kernel/signal.c:712
> >> [<ffffffff81006685>] exit_to_usermode_loop+0x1a5/0x210
> >> arch/x86/entry/common.c:247
> >> [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282
> >> [<ffffffff8100866a>] syscall_return_slowpath+0x2ba/0x340
> >> arch/x86/entry/common.c:344
> >> [<ffffffff866d18e2>] int_ret_from_sys_call+0x25/0x9f
> >> arch/x86/entry/entry_64.S:281
> >> Code: c0 0f 84 91 00 00 00 48 b8 00 02 00 00 00 00 ad de 48 39 c3 0f
> >> 84 9f 00 00 00 48 89 da 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80>
> >> 3c 02 00 0f 85 f6 00 00 00 4c 8b 23 4c 39 e1 0f 85 95 00 00
> >> RIP [<ffffffff82c88e16>] __list_del_entry+0x86/0x1e0 lib/list_debug.c:57
> >> RSP <ffff88006d707cd0>
> >> ---[ end trace fd16e1eaa1720656 ]---
> >> Kernel panic - not syncing: Fatal exception in interrupt
> >> Shutting down cpus with NMI
> >> Kernel Offset: disabled
> >> ---[ end Kernel panic - not syncing: Fatal exception in interrupt
> >>
> >>
> >> It is not easily reproducible. I've hit several times while running
> >> fuzzer for a week. Here is one of the logs for the record:
> >> https://gist.githubusercontent.com/dvyukov/c84798ee55721563ecb537c4d51dc9f5/raw/f00b865a85877656f13b41917f7321730f140d35/gistfile1.txt
> >
> > There are a few more fixes in sound/core/timer.c since 4.5, and they
> > possibly already cover this.
> >
> > Please let me know if this is still seen on the upcoming 4.6-rc2.
>
> Hi Takashi,
>
> I've updated fuzzer to 05cf8077e54b20dddb756eaa26f3aeb5c38dd3cf (Apr
> 1) yesterday. Let's see if it still happens.
>
> Out of curiosity, how was the bug found?

Well, I'm not entirely sure whether they really cover. It's just a
hope, as these are patches to close some possible races :)

9984d1b5835ca29fc7025186a891ee7398d21cc7
ALSA: timer: Protect the whole snd_timer_close() with open race
f65e0d299807d8a11812845c972493c3f9a18e10
ALSA: timer: Call notifier in the same spinlock
4a07083ed613644c96c34a7dd2853dc5d7c70902
ALSA: timer: Use mod_timer() for rearming the system timer

Takashi

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