Re: [PATCH] HID: hid-lg4ff: Fix uninit-value set_autocenter_default

[Phong Tran]

On 11/18/19 4:43 PM, Benjamin Tissoires wrote:
> On Tue, Nov 5, 2019 at 3:18 PM Phong Tran <tranmanphong@xxxxxxxxx> wrote:
> > syzbot found a problem using of uinit pointer in
> > lg4ff_set_autocenter_default().
> >
> > Reported-by: syzbot+1234691fec1b8ceba8b1@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > Tested by syzbot:
> >
> > https://groups.google.com/d/msg/syzkaller-bugs/ApnMLW6sfKE/Qq0bIHGEAQAJ
>
> This seems weird to me:
>
> the syzbot link above is about `hid_get_drvdata(hid)`, and, as I read
> it, the possibility that hid might not have an initialized value.

In the dashboard [1] shows
BUG: KMSAN: uninit-value in dev_get_drvdata include/linux/device.h:1388 
[inline]
BUG: KMSAN: uninit-value in hid_get_drvdata include/linux/hid.h:628 [inline]
BUG: KMSAN: uninit-value in lg4ff_set_autocenter_default+0x23a/0xa20 
drivers/hid/hid-lg4ff.c:477
base on that I did the initialization the pointer in the patch.

> Here you are changing the initialized values of value, entry and
> drv_data, all 3 are never used before their first assignment.
>
> I have a feeling this particular syzbot check has already been fixed
> upstream by d9d4b1e46d95 "HID: Fix assumption that devices have
> inputs".

I think the commit d9d4b1 fixed this report [2] by syzbot.

[1] https://syzkaller.appspot.com/bug?extid=1234691fec1b8ceba8b1
[2] https://syzkaller.appspot.com/bug?extid=403741a091bf41d4ae79

regards,
Phong.
> Cheers,
> Benjamin
>
> > Signed-off-by: Phong Tran <tranmanphong@xxxxxxxxx>
> > ---
> >   drivers/hid/hid-lg4ff.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hid/hid-lg4ff.c b/drivers/hid/hid-lg4ff.c
> > index 5e6a0cef2a06..44dfd08b0c32 100644
> > --- a/drivers/hid/hid-lg4ff.c
> > +++ b/drivers/hid/hid-lg4ff.c
> > @@ -468,10 +468,10 @@ static int lg4ff_play(struct input_dev *dev, void *data, struct ff_effect *effec
> >   static void lg4ff_set_autocenter_default(struct input_dev *dev, u16 magnitude)
> >   {
> >          struct hid_device *hid = input_get_drvdata(dev);
> > -       s32 *value;
> > +       s32 *value = NULL;
> >          u32 expand_a, expand_b;
> > -       struct lg4ff_device_entry *entry;
> > -       struct lg_drv_data *drv_data;
> > +       struct lg4ff_device_entry *entry = NULL;
> > +       struct lg_drv_data *drv_data = NULL;
> >          unsigned long flags;
> >
> >          drv_data = hid_get_drvdata(hid);
> > --
> > 2.20.1