Re: KMSAN: uninit-value in snd_midi_event_encode_byte

[Takashi Iwai]

On Mon, 03 Sep 2018 15:33:12 +0200,
Dmitry Vyukov wrote:
> 
> 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.

OK, it would have been helpful if the description there was more clear
:)

And no automated way for that?  I mean, I already attached patch in
the previous reply (together with syz-magic command to point the git
branch URL).  Do I need anything else?


thanks,

Takashi