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SubjectRe: Re: KMSAN: uninit-value in snd_midi_event_encode_byte
From
> 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.



> Takashi

> -- 8< --
> From: Takashi Iwai <tiwai@suse.de>
> Subject: [PATCH] ALSA: rawmidi: Initialize allocated buffers

> syzbot reported the uninitialized value exposure in certain situations
> using virmidi loop. It's likely a very small race at writing and
> reading, and the influence is almost negligible. But it's safer to
> paper over this just by replacing the existing kvmalloc() with
> kvzalloc().

> Reported-by: syzbot+194dffdb8b22fc5d207a@syzkaller.appspotmail.com
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
> sound/core/rawmidi.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)

> diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
> index 69517e18ef07..08d5662039e3 100644
> --- a/sound/core/rawmidi.c
> +++ b/sound/core/rawmidi.c
> @@ -129,7 +129,7 @@ static int snd_rawmidi_runtime_create(struct
> snd_rawmidi_substream *substream)
> runtime->avail = 0;
> else
> runtime->avail = runtime->buffer_size;
> - runtime->buffer = kvmalloc(runtime->buffer_size, GFP_KERNEL);
> + runtime->buffer = kvzalloc(runtime->buffer_size, GFP_KERNEL);
> if (!runtime->buffer) {
> kfree(runtime);
> return -ENOMEM;
> @@ -655,7 +655,7 @@ static int resize_runtime_buffer(struct
> snd_rawmidi_runtime *runtime,
> if (params->avail_min < 1 || params->avail_min > params->buffer_size)
> return -EINVAL;
> if (params->buffer_size != runtime->buffer_size) {
> - newbuf = kvmalloc(params->buffer_size, GFP_KERNEL);
> + newbuf = kvzalloc(params->buffer_size, GFP_KERNEL);
> if (!newbuf)
> return -ENOMEM;
> spin_lock_irq(&runtime->lock);
> --
> 2.18.0

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