Re: KMSAN: uninit-value in snd_midi_event_encode_byte

[Dmitry Vyukov]

On Mon, Sep 3, 2018 at 3:29 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Mon, 03 Sep 2018 15:22:42 +0200,
> syzbot wrote:
>>
>> > On Mon, 03 Sep 2018 03:53:03 +0200,
>> > syzbot wrote:
>>
>> >> syzbot has found a reproducer for the following crash on:
>>
>> >> HEAD commit:    28f0ca98eadf kmsan: don't instrument
>> >> do_syscall_64() and  _..
>> >> git tree:       https://github.com/google/kmsan.git/master
>> >> console output: https://syzkaller.appspot.com/x/log.txt?x=10556c92400000
>> >> kernel config:
>> >> https://syzkaller.appspot.com/x/.config?x=3431f03869413153
>> >> dashboard link:
>> >> https://syzkaller.appspot.com/bug?extid=194dffdb8b22fc5d207a
>> >> compiler:       clang version 8.0.0 (trunk 339414)
>> >> syz repro:
>> >> https://syzkaller.appspot.com/x/repro.syz?x=123a520a400000
>> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16068dc1400000
>>
>> >> IMPORTANT: if you fix the bug, please add the following tag to the
>> >> commit:
>> >> Reported-by: syzbot+194dffdb8b22fc5d207a@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> >> ==================================================================
>> >> BUG: KMSAN: uninit-value in snd_midi_event_encode_byte+0x569/0xff0
>> >> sound/core/seq/seq_midi_event.c:195
>> >> CPU: 1 PID: 1659 Comm: kworker/1:1H Not tainted 4.19.0-rc1+ #40
>> >> Hardware name: Google Google Compute Engine/Google Compute Engine,
>> >> BIOS  Google 01/01/2011
>> >> Workqueue: events_highpri snd_vmidi_output_work
>> >> Call Trace:
>> >>   __dump_stack lib/dump_stack.c:77 [inline]
>> >>   dump_stack+0x14b/0x190 lib/dump_stack.c:113
>> >>   kmsan_report+0x183/0x2b0 mm/kmsan/kmsan.c:956
>> >>   __msan_warning+0x70/0xc0 mm/kmsan/kmsan_instr.c:645
>> >>   snd_midi_event_encode_byte+0x569/0xff0
>> >> sound/core/seq/seq_midi_event.c:195
>> >>   snd_vmidi_output_work+0x34e/0x5b0 sound/core/seq/seq_virmidi.c:161
>> >>   process_one_work+0x1605/0x1f40 kernel/workqueue.c:2153
>> >>   worker_thread+0x11a2/0x2590 kernel/workqueue.c:2296
>> >>   kthread+0x465/0x4a0 kernel/kthread.c:247
>> >>   ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:416
>>
>> >> Uninit was stored to memory at:
>> >>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:256 [inline]
>> >>   kmsan_save_stack mm/kmsan/kmsan.c:271 [inline]
>> >>   kmsan_internal_chain_origin+0x128/0x210 mm/kmsan/kmsan.c:573
>> >>   __msan_chain_origin+0x69/0xc0 mm/kmsan/kmsan_instr.c:482
>> >>   __snd_rawmidi_transmit_peek sound/core/rawmidi.c:1103 [inline]
>> >>   snd_rawmidi_transmit+0xa75/0xbf0 sound/core/rawmidi.c:1228
>> >>   snd_vmidi_output_work+0x2ac/0x5b0 sound/core/seq/seq_virmidi.c:159
>> >>   process_one_work+0x1605/0x1f40 kernel/workqueue.c:2153
>> >>   worker_thread+0x11a2/0x2590 kernel/workqueue.c:2296
>> >>   kthread+0x465/0x4a0 kernel/kthread.c:247
>> >>   ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:416
>>
>> >> Uninit was created at:
>> >>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:256 [inline]
>> >>   kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:181
>> >>   kmsan_kmalloc+0x98/0x100 mm/kmsan/kmsan_hooks.c:91
>> >>   __kmalloc_node+0x7bf/0x11c0 mm/slub.c:3828
>> >>   kmalloc_node include/linux/slab.h:555 [inline]
>> >>   kvmalloc_node+0x19d/0x3e0 mm/util.c:423
>> >>   kvmalloc include/linux/mm.h:577 [inline]
>> >>   snd_rawmidi_runtime_create sound/core/rawmidi.c:132 [inline]
>> >>   open_substream+0x3c8/0xaa0 sound/core/rawmidi.c:276
>> >>   rawmidi_open_priv+0x347/0x1000 sound/core/rawmidi.c:327
>> >>   snd_rawmidi_open+0x7d4/0x1120 sound/core/rawmidi.c:424
>> >>   soundcore_open+0x9be/0xa60 sound/sound_core.c:597
>> >>   chrdev_open+0xc26/0xdb0 fs/char_dev.c:417
>> >>   do_dentry_open+0xce6/0x1740 fs/open.c:771
>> >>   vfs_open+0xaf/0xe0 fs/open.c:880
>> >>   do_last fs/namei.c:3418 [inline]
>> >>   path_openat+0x1799/0x6870 fs/namei.c:3534
>> >>   do_filp_open+0x259/0x610 fs/namei.c:3564
>> >>   do_sys_open+0x630/0x940 fs/open.c:1063
>> >>   __do_sys_open fs/open.c:1081 [inline]
>> >>   __se_sys_open+0xad/0xc0 fs/open.c:1076
>> >>   __x64_sys_open+0x4a/0x70 fs/open.c:1076
>> >>   do_syscall_64+0xb8/0x100 arch/x86/entry/common.c:291
>> >>   entry_SYSCALL_64_after_hwframe+0x63/0xe7
>> >> ==================================================================
>>
>> > This looks like some small race at virmidi reading and the buffer
>> > handling, which should be almost harmless by itself.
>> > Nevertheless, the fix should be easy, just replacing kvmalloc() with
>> > kvzalloc(), as below.
>>
>> > Let's check whether this works.
>>
>> > #syz test:
>> > git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git
>> > topic/rawmidi-fixes
>>
>> KMSAN bugs can only be tested on https://github.com/google/kmsan.git tree
>> because KMSAN tool is not upstreamed yet.
>> See
>> https://github.com/google/syzkaller/blob/master/docs/syzbot.md#kmsan-bugs
>> for details.
>
> So how is the procedure to test a patch for bugs spotted by KMSAN?
>
> In this case, the fix is trivial, so I can put it to my tree for the
> next pull request.  Of course, it'd be better if it can be confirmed
> to work beforehand...

https://github.com/google/syzkaller/blob/master/docs/syzbot.md#kmsan-bugs

Which means you need to attach a patch because it's not in that tree.