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
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);