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SubjectRe: KMSAN: uninit-value in snd_midi_event_encode_byte
On Mon, 03 Sep 2018 15:33:12 +0200,
Dmitry Vyukov wrote:
>
> On Mon, Sep 3, 2018 at 3:29 PM, Takashi Iwai <tiwai@suse.de> 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@syzkaller.appspotmail.com
> >>
> >> >> ==================================================================
> >> >> 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

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