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. #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; }
