On 5/21/19 8:15 PM, Vandana BN wrote: > SyzKaller hit the null pointer deref while reading from uninitialized > udev->product in zr364xx_vidioc_querycap(). > ================================================================== > BUG: KASAN: null-ptr-deref in read_word_at_a_time+0xe/0x20 > include/linux/compiler.h:274 > Read of size 1 at addr 0000000000000000 by task v4l_id/5287 > > CPU: 1 PID: 5287 Comm: v4l_id Not tainted 5.1.0-rc3-319004-g43151d6 #6 > 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+0xe8/0x16e lib/dump_stack.c:113 > kasan_report.cold+0x5/0x3c mm/kasan/report.c:321 > read_word_at_a_time+0xe/0x20 include/linux/compiler.h:274 > strscpy+0x8a/0x280 lib/string.c:207 > zr364xx_vidioc_querycap+0xb5/0x210 drivers/media/usb/zr364xx/zr364xx.c:706 > v4l_querycap+0x12b/0x340 drivers/media/v4l2-core/v4l2-ioctl.c:1062 > __video_do_ioctl+0x5bb/0xb40 drivers/media/v4l2-core/v4l2-ioctl.c:2874 > video_usercopy+0x44e/0xf00 drivers/media/v4l2-core/v4l2-ioctl.c:3056 > v4l2_ioctl+0x14e/0x1a0 drivers/media/v4l2-core/v4l2-dev.c:364 > vfs_ioctl fs/ioctl.c:46 [inline] > file_ioctl fs/ioctl.c:509 [inline] > do_vfs_ioctl+0xced/0x12f0 fs/ioctl.c:696 > ksys_ioctl+0xa0/0xc0 fs/ioctl.c:713 > __do_sys_ioctl fs/ioctl.c:720 [inline] > __se_sys_ioctl fs/ioctl.c:718 [inline] > __x64_sys_ioctl+0x74/0xb0 fs/ioctl.c:718 > do_syscall_64+0xcf/0x4f0 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x7f3b56d8b347 > Code: 90 90 90 48 8b 05 f1 fa 2a 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff > ff c3 90 90 90 90 90 90 90 90 90 90 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff > ff 73 01 c3 48 8b 0d c1 fa 2a 00 31 d2 48 29 c2 64 > RSP: 002b:00007ffe005d5d68 EFLAGS: 00000202 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f3b56d8b347 > RDX: 00007ffe005d5d70 RSI: 0000000080685600 RDI: 0000000000000003 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000400884 > R13: 00007ffe005d5ec0 R14: 0000000000000000 R15: 0000000000000000 > ================================================================== > > For this device udev->product is not initialized and accessing it causes a NULL pointer deref. > > The fix is to check for NULL before strscpy() and copy empty string, if > product is NULL > > Reported-by: syzbot+66010012fd4c531a1a96@xxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Vandana BN <bnvandana@xxxxxxxxx> > --- > drivers/media/usb/zr364xx/zr364xx.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/media/usb/zr364xx/zr364xx.c b/drivers/media/usb/zr364xx/zr364xx.c > index 96fee8d5b865..401a1e55dbe1 100644 > --- a/drivers/media/usb/zr364xx/zr364xx.c > +++ b/drivers/media/usb/zr364xx/zr364xx.c > @@ -703,7 +703,10 @@ static int zr364xx_vidioc_querycap(struct file *file, void *priv, > struct zr364xx_camera *cam = video_drvdata(file); > > strscpy(cap->driver, DRIVER_DESC, sizeof(cap->driver)); > - strscpy(cap->card, cam->udev->product, sizeof(cap->card)); > + if (cam->udev->product) > + strscpy(cap->card, cam->udev->product, sizeof(cap->card)); > + else > + strscpy(cap->card, "", sizeof(cap->card)); You can drop the 'else' part since cap->card is already zeroed by the V4L2 core framework. Looks good otherwise! Regards, Hans > strscpy(cap->bus_info, dev_name(&cam->udev->dev), > sizeof(cap->bus_info)); > cap->device_caps = V4L2_CAP_VIDEO_CAPTURE | >
