On Fri, 26 Jun 2020 20:26:05 +0200, Alan Stern wrote:

On Fri, Jun 26, 2020 at 10:18:12AM -0700, syzbot wrote:

...

Hello,

syzbot found the following crash on:

HEAD commit: fb574682 usbip: tools: fix module name in man page git tree: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing console output: https://syzkaller.appspot.com/x/log.txt?x=156560b1100000 kernel config: https://syzkaller.appspot.com/x/.config?x=63b40b2ae167bad6 dashboard link: https://syzkaller.appspot.com/bug?extid=145012a46658ac00fc9e compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+145012a46658ac00fc9e@syzkaller.appspotmail.com

snd_usb_toneport 5-1:0.0: URB in #0 submission failed (-19) snd_usb_toneport 5-1:0.0: URB in #0 submission failed (-19) snd_usb_toneport 5-1:0.0: URB in #0 submission failed (-19) snd_usb_toneport 5-1:0.0: URB in #0 submission failed (-19) ================================================================== BUG: KASAN: use-after-free in line6_submit_audio_in_all_urbs+0x10b/0x120 sound/usb/line6/capture.c:72 Read of size 8 at addr ffff8881cffb1800 by task kworker/1:5/3257

CPU: 1 PID: 3257 Comm: kworker/1:5 Not tainted 5.8.0-rc1-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events line6_startup_work Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xf6/0x16e lib/dump_stack.c:118 print_address_description.constprop.0+0x1a/0x210 mm/kasan/report.c:383 __kasan_report mm/kasan/report.c:513 [inline] kasan_report.cold+0x37/0x7c mm/kasan/report.c:530 line6_submit_audio_in_all_urbs+0x10b/0x120 sound/usb/line6/capture.c:72 line6_stream_start+0x207/0x230 sound/usb/line6/pcm.c:197 line6_pcm_acquire+0x161/0x210 sound/usb/line6/pcm.c:318 line6_startup_work+0x42/0x50 sound/usb/line6/driver.c:734 process_one_work+0x94c/0x15f0 kernel/workqueue.c:2269 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415 kthread+0x392/0x470 kernel/kthread.c:291 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Allocated by task 76: save_stack+0x1b/0x40 mm/kasan/common.c:48 set_track mm/kasan/common.c:56 [inline] __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494 kmalloc include/linux/slab.h:555 [inline] kzalloc include/linux/slab.h:669 [inline] line6_init_pcm+0x2a7/0x9e0 sound/usb/line6/pcm.c:533 toneport_init+0xdd/0x6b0 sound/usb/line6/toneport.c:419 line6_probe+0xaa0/0x1330 sound/usb/line6/driver.c:809

It look like the cancel_delayed_work() in line6_disconnect() needs to be cancel_delayed_work_sync(). Unfortunately we can't test this until syzbot is able to reproduce the bug.

Right, but fixing it now wouldn't be bad. The fix patch below.

thanks,

Takashi

-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: line6: Sync the pending work cancel at disconnection

Recently syzkaller reported a UAF in LINE6 driver, and it's likely because we call cancel_delayed_work() at the disconnect callback instead of cancel_delayed_work_sync(). Let's use the correct one instead.

Reported-by: syzbot+145012a46658ac00fc9e@syzkaller.appspotmail.com Suggested-by: Alan Stern stern@rowland.harvard.edu Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/usb/line6/driver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c index 7629116f570e..2746d9698180 100644 --- a/sound/usb/line6/driver.c +++ b/sound/usb/line6/driver.c @@ -840,7 +840,7 @@ void line6_disconnect(struct usb_interface *interface) if (WARN_ON(usbdev != line6->usbdev)) return;

- cancel_delayed_work(&line6->startup_work); + cancel_delayed_work_sync(&line6->startup_work);

if (line6->urb_listen != NULL) line6_stop_listen(line6);