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Tue, 10 Dec 2019 11:48:02 -0800 (PST) Date: Tue, 10 Dec 2019 11:48:02 -0800 In-Reply-To: X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <000000000000441a4205995eca11@google.com> Subject: Re: Re: KASAN: use-after-free Read in usbvision_v4l2_open From: syzbot To: Alan Stern Cc: andreyknvl@google.com, hverkuil@xs4all.nl, jrdr.linux@gmail.com, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-usb@vger.kernel.org, mchehab@kernel.org, rfontana@redhat.com, stern@rowland.harvard.edu, syzkaller-bugs@googlegroups.com, tglx@linutronix.de Content-Type: text/plain; charset="UTF-8"; format=flowed; delsp=yes Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org > 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@syzkaller.appspotmail.com >> ================================================================== >> 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. > 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; > }