Re: sound: use-after-free in snd_timer_start1

From: Takashi Iwai
Date: Thu Feb 04 2016 - 11:35:00 EST

On Thu, 04 Feb 2016 17:32:31 +0100,
Dmitry Vyukov wrote:
>
> On Thu, Feb 4, 2016 at 5:24 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> > On Wed, 03 Feb 2016 17:24:56 +0100,
> > Dmitry Vyukov wrote:
> >>
> >> Hello,
> >>
> >> The following program triggers use-after-free in snd_timer_start1:
> >>
> >> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> >> #include <pthread.h>
> >> #include <stdint.h>
> >> #include <string.h>
> >> #include <sys/syscall.h>
> >> #include <unistd.h>
> >>
> >> int main()
> >> {
> >> syscall(SYS_mmap, 0x20000000ul, 0x664000ul, 0x3ul, 0x32ul,
> >> 0xfffffffffffffffful, 0x0ul);
> >> int fd = syscall(SYS_open, "/dev/snd/timer", 0x40000ul, 0, 0, 0);
> >> *(uint32_t*)0x20653000 = (uint32_t)0x1;
> >> *(uint32_t*)0x20653004 = (uint32_t)0xfffffffffffffffe;
> >> *(uint32_t*)0x20653008 = (uint32_t)0x8;
> >> *(uint32_t*)0x2065300c = (uint32_t)0x0;
> >> *(uint32_t*)0x20653010 = (uint32_t)0x0;
> >> *(uint8_t*)0x20653014 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653015 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653016 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653017 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653018 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653019 = (uint8_t)0x0;
> >> *(uint8_t*)0x2065301a = (uint8_t)0x0;
> >> *(uint8_t*)0x2065301b = (uint8_t)0x0;
> >> *(uint8_t*)0x2065301c = (uint8_t)0x0;
> >> *(uint8_t*)0x2065301d = (uint8_t)0x0;
> >> *(uint8_t*)0x2065301e = (uint8_t)0x0;
> >> *(uint8_t*)0x2065301f = (uint8_t)0x0;
> >> *(uint8_t*)0x20653020 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653021 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653022 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653023 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653024 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653025 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653026 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653027 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653028 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653029 = (uint8_t)0x0;
> >> *(uint8_t*)0x2065302a = (uint8_t)0x0;
> >> *(uint8_t*)0x2065302b = (uint8_t)0x0;
> >> *(uint8_t*)0x2065302c = (uint8_t)0x0;
> >> *(uint8_t*)0x2065302d = (uint8_t)0x0;
> >> *(uint8_t*)0x2065302e = (uint8_t)0x0;
> >> *(uint8_t*)0x2065302f = (uint8_t)0x0;
> >> *(uint8_t*)0x20653030 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653031 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653032 = (uint8_t)0x0;
> >> *(uint8_t*)0x20653033 = (uint8_t)0x0;
> >> syscall(SYS_ioctl, fd, 0x40345410ul, 0x20653000ul, 0, 0, 0);
> >> syscall(SYS_ioctl, fd, 0x54a0ul, 0, 0, 0, 0);
> >> return 0;
> >> }
> >>
> >> ==================================================================
> >> BUG: KASAN: use-after-free in __list_add+0x233/0x22016/02/03 13:44:32
> >> executing program 0:
> >> Read of size 8 by task syz-executor/27661
> >>
> >> INFO: Allocated in snd_timer_instance_new+0x52/0x3a0 age=7 cpu=0 pid=27660
> >> [< inline >] slab_alloc_node mm/slub.c:2562
> >> [< inline >] slab_alloc mm/slub.c:2604
> >> [< none >] kmem_cache_alloc_trace+0x25c/0x300 mm/slub.c:2621
> >> [< 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:1598
> >> [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1874
> >> [< none >] snd_timer_user_ioctl+0x8db/0x25f0 sound/core/timer.c:1904
> >> [< 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=3 pid=27661
> >> [< inline >] slab_free mm/slub.c:2835
> >> [< none >] kfree+0x2ac/0x2c0 mm/slub.c:3664
> >> [< none >] snd_timer_close+0x3ee/0x750 sound/core/timer.c:375
> >> [< inline >] snd_timer_user_tselect sound/core/timer.c:1588
> >> [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1874
> >> [< none >] snd_timer_user_ioctl+0x7b6/0x25f0 sound/core/timer.c:1904
> >> [< 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
> >>
> >> Call Trace:
> >> [< inline >] kasan_report mm/kasan/report.c:274
> >> [<ffffffff8176640e>] __asan_report_load8_noabort+0x3e/0x40
> >> mm/kasan/report.c:295
> >> [<ffffffff82c4a7e3>] __list_add+0x233/0x250 lib/list_debug.c:39
> >> [< inline >] list_move_tail include/linux/list.h:77
> >> [<ffffffff85240fdc>] snd_timer_start1+0x6c/0x2c0 sound/core/timer.c:432
> >> [<ffffffff85241a7b>] snd_timer_start+0x20b/0x2b0 sound/core/timer.c:499
> >> [< inline >] snd_timer_user_start sound/core/timer.c:1799
> >> [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1883
> >> [<ffffffff85245fb7>] snd_timer_user_ioctl+0x767/0x25f0 sound/core/timer.c:1904
> >> [< inline >] vfs_ioctl fs/ioctl.c:43
> >> [<ffffffff817fa9ec>] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674
> >> [< inline >] SYSC_ioctl fs/ioctl.c:689
> >> [<ffffffff817fb89f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680
> >> [<ffffffff8665ebb6>] entry_SYSCALL_64_fastpath+0x16/0x7a
> >> arch/x86/entry/entry_64.S:185
> >> ==================================================================
> >>
> >>
> >> Sometimes it manifests as:
> >>
> >> ------------[ cut here ]------------
> >> WARNING: CPU: 1 PID: 6548 at lib/list_debug.c:42 __list_add+0x1db/0x250()
> >> list_add corruption. prev->next should be next (ffff8800697c10e8), but
> >> was ffff880030441fd0. (prev=ffff880030441fd0).
> >> Modules linked in:
> >> CPU: 1 PID: 6548 Comm: a.out Not tainted 4.5.0-rc2+ #309
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >> 00000000ffffffff ffff88002fa17918 ffffffff82be2c8d ffff88002fa17988
> >> ffff88002fd62f80 ffffffff86acf380 ffff88002fa17958 ffffffff81355139
> >> ffffffff82c4a78b ffffed0005f42f2d ffffffff86acf380 000000000000002a
> >> Call Trace:
> >> [< inline >] __dump_stack lib/dump_stack.c:15
> >> [<ffffffff82be2c8d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
> >> [<ffffffff81355139>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
> >> [<ffffffff81355249>] warn_slowpath_fmt+0xa9/0xd0 kernel/panic.c:494
> >> [<ffffffff82c4a78b>] __list_add+0x1db/0x250 lib/list_debug.c:39
> >> [< inline >] list_move_tail include/linux/list.h:77
> >> [<ffffffff85240fdc>] snd_timer_start1+0x6c/0x2c0 sound/core/timer.c:432
> >> [<ffffffff85241a7b>] snd_timer_start+0x20b/0x2b0 sound/core/timer.c:499
> >> [< inline >] snd_timer_user_start sound/core/timer.c:1799
> >> [< inline >] __snd_timer_user_ioctl sound/core/timer.c:1883
> >> [<ffffffff85245fb7>] snd_timer_user_ioctl+0x767/0x25f0 sound/core/timer.c:1904
> >> [< inline >] vfs_ioctl fs/ioctl.c:43
> >> [<ffffffff817fa9ec>] do_vfs_ioctl+0x18c/0xfb0 fs/ioctl.c:674
> >> [< inline >] SYSC_ioctl fs/ioctl.c:689
> >> [<ffffffff817fb89f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:680
> >> [<ffffffff8665ebb6>] entry_SYSCALL_64_fastpath+0x16/0x7a
> >> arch/x86/entry/entry_64.S:185
> >> ---[ end trace 77da812dd399e78b ]---
> >>
> >> On commit 34229b277480f46c1e9a19f027f30b074512e68b + recent fixes from Takashi.
> >
> > Thanks for the report. This is indeed an old bug, but it appears now
> > more easily due to the recent fix to avoid double-stop. Below is the
> > fix patch. topic/core-fixes branch was updated with this, too.
>
>
> Fixes the crash for me.
> I think this was the last one in sound that happened periodically
> during fuzzing. Let's see what the fuzzer will say now :)
> Thanks for quick fixes!

Great, thanks for your patient reports and testing!


Takashi