On Tue, Dec 10, 2019 at 9:17 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, 10 Dec 2019, syzbot wrote: > > > > On Mon, 9 Dec 2019, syzbot wrote: > > > > >> Hello, > > > > >> syzbot found the following crash on: > > > > >> HEAD commit: 1f22d15c usb: gadget: add raw-gadget interface > > >> git tree: https://github.com/google/kasan.git usb-fuzzer > > >> console output: https://syzkaller.appspot.com/x/log.txt?x=1296f42ae00000 > > >> kernel config: > > >> https://syzkaller.appspot.com/x/.config?x=8ccee2968018adcb > > >> dashboard link: > > >> https://syzkaller.appspot.com/bug?extid=c7b0ec009a216143df30 > > >> compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > >> 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+c7b0ec009a216143df30@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > >> ================================================================== > > >> BUG: KASAN: use-after-free in __mutex_lock_common > > >> kernel/locking/mutex.c:1043 [inline] > > >> BUG: KASAN: use-after-free in __mutex_lock+0x124d/0x1360 > > >> kernel/locking/mutex.c:1106 > > >> Read of size 8 at addr ffff8881cad4d8b8 by task v4l_id/4526 > > > > >> CPU: 0 PID: 4526 Comm: v4l_id Not tainted 5.4.0-syzkaller #0 > > >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > >> Google 01/01/2011 > > >> Call Trace: > > >> __dump_stack lib/dump_stack.c:77 [inline] > > >> dump_stack+0xef/0x16e lib/dump_stack.c:118 > > >> print_address_description.constprop.0+0x36/0x50 mm/kasan/report.c:374 > > >> __kasan_report.cold+0x1a/0x33 mm/kasan/report.c:506 > > >> kasan_report+0xe/0x20 mm/kasan/common.c:638 > > >> __mutex_lock_common kernel/locking/mutex.c:1043 [inline] > > >> __mutex_lock+0x124d/0x1360 kernel/locking/mutex.c:1106 > > >> usbvision_v4l2_open+0x77/0x340 > > >> drivers/media/usb/usbvision/usbvision-video.c:314 > > >> v4l2_open+0x20f/0x3d0 drivers/media/v4l2-core/v4l2-dev.c:423 > > >> chrdev_open+0x219/0x5c0 fs/char_dev.c:414 > > >> do_dentry_open+0x494/0x1120 fs/open.c:797 > > >> do_last fs/namei.c:3412 [inline] > > >> path_openat+0x142b/0x4030 fs/namei.c:3529 > > >> do_filp_open+0x1a1/0x280 fs/namei.c:3559 > > >> do_sys_open+0x3c0/0x580 fs/open.c:1097 > > >> do_syscall_64+0xb7/0x5b0 arch/x86/entry/common.c:294 > > >> entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > > > This looks like a race in v4l2_open(): The function drops the > > > videodev_lock mutex before calling the video driver's open routine, and > > > the device can be unregistered during the short time between. > > > > > This patch tries to make the race much more likely to happen, for > > > testing and verification. > > > > > Andrey, will syzbot run the same test with this patch, even though it > > > says it doesn't have a reproducer? > > > > > Alan Stern > > > > > #syz test: https://github.com/google/kasan.git 1f22d15c > > > > This crash does not have a reproducer. I cannot test it. > > Let's try the same patch with a different bug report -- one that has a > reproducer. I assume that syzbot gets the bug identity from the > email's From: line (which has been updated acoordingly) rather than the > Subject: line. Did you get a response for this test? I see the test attempt on the dashboard (the patch failed to build), but I didn't get an email with the result. > > #syz test: https://github.com/google/kasan.git 1f22d15c > > Index: usb-devel/drivers/media/usb/usbvision/usbvision-video.c > =================================================================== > --- usb-devel.orig/drivers/media/usb/usbvision/usbvision-video.c > +++ usb-devel/drivers/media/usb/usbvision/usbvision-video.c > @@ -1585,6 +1585,7 @@ static void usbvision_disconnect(struct > wake_up_interruptible(&usbvision->wait_frame); > wake_up_interruptible(&usbvision->wait_stream); > } else { > + msleep(100); > usbvision_release(usbvision); > } > > Index: usb-devel/drivers/media/v4l2-core/v4l2-dev.c > =================================================================== > --- usb-devel.orig/drivers/media/v4l2-core/v4l2-dev.c > +++ usb-devel/drivers/media/v4l2-core/v4l2-dev.c > @@ -419,9 +419,10 @@ static int v4l2_open(struct inode *inode > video_get(vdev); > mutex_unlock(&videodev_lock); > if (vdev->fops->open) { > - if (video_is_registered(vdev)) > + if (video_is_registered(vdev)) { > + msleep(200); > ret = vdev->fops->open(filp); > - else > + } else > ret = -ENODEV; > } > >
