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From:   Benjamin Tissoires <benjamin.tissoires@redhat.com>
Date:   Mon, 25 Nov 2019 16:14:31 +0100
Message-ID: <CAO-hwJ+r+n4Dy+jqSuCk-vApfP-PR4o2oTzt4XWxH5jUQOeFwA@mail.gmail.com>
Subject: Re: [PATCH] HID: hid-lg4ff: Fix uninit-value set_autocenter_default
To:     Phong Tran <tranmanphong@gmail.com>
Cc:     "open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot <syzbot+1234691fec1b8ceba8b1@syzkaller.appspotmail.com>
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On Tue, Nov 19, 2019 at 2:30 PM Phong Tran <tranmanphong@gmail.com> wrote:
>
> On 11/18/19 4:43 PM, Benjamin Tissoires wrote:
> > On Tue, Nov 5, 2019 at 3:18 PM Phong Tran <tranmanphong@gmail.com> wrot=
e:
> >>
> >> syzbot found a problem using of uinit pointer in
> >> lg4ff_set_autocenter_default().
> >>
> >> Reported-by: syzbot+1234691fec1b8ceba8b1@syzkaller.appspotmail.com
> >>
> >> Tested by syzbot:
> >>
> >> https://groups.google.com/d/msg/syzkaller-bugs/ApnMLW6sfKE/Qq0bIHGEAQA=
J
> >
> > 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 [inli=
ne]
> 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=3D1234691fec1b8ceba8b1
> [2] https://syzkaller.appspot.com/bug?extid=3D403741a091bf41d4ae79

As you can see in my long discussion with syzbot today, d9d4b1 also
fixed that one.

https://groups.google.com/forum/#!msg/syzkaller-bugs/ApnMLW6sfKE/Qq0bIHGEAQ=
AJ

Cheers,
Benjamin

>
> regards,
> Phong.
> > Cheers,
> > Benjamin
> >
> >>
> >> Signed-off-by: Phong Tran <tranmanphong@gmail.com>
> >> ---
> >>   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, voi=
d *data, struct ff_effect *effec
> >>   static void lg4ff_set_autocenter_default(struct input_dev *dev, u16 =
magnitude)
> >>   {
> >>          struct hid_device *hid =3D input_get_drvdata(dev);
> >> -       s32 *value;
> >> +       s32 *value =3D NULL;
> >>          u32 expand_a, expand_b;
> >> -       struct lg4ff_device_entry *entry;
> >> -       struct lg_drv_data *drv_data;
> >> +       struct lg4ff_device_entry *entry =3D NULL;
> >> +       struct lg_drv_data *drv_data =3D NULL;
> >>          unsigned long flags;
> >>
> >>          drv_data =3D hid_get_drvdata(hid);
> >> --
> >> 2.20.1
> >>
> >
>