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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Wed, 6 Nov 2019 13:11:09 +0100
Message-ID: <CAAeHK+zzio=k6aN8rX2meYk1bWiE_TvyzovRkGXm01fbCc_nwA@mail.gmail.com>
Subject: Re: [PATCH] usb: appledisplay: fix use-after-free in bl_get_brightness
To:     Phong Tran <tranmanphong@gmail.com>
Cc:     syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com, 2pi@mok.nu,
        alex.theissen@me.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        linux-kernel-mentees@lists.linuxfoundation.org
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On Wed, Nov 6, 2019 at 1:10 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> On Wed, Nov 6, 2019 at 12:37 AM Phong Tran <tranmanphong@gmail.com> wrote:
> >
> > In context of USB disconnect, the delaywork trigger and calling
> > appledisplay_bl_get_brightness() and the msgdata was freed.
> >
> > add the checking return value of usb_control_msg() and only update the
> > data while the retval is valid.
> >
> > Reported-by: syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com
> > Reported-and-tested-by:
> > syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com
> >
> > https://groups.google.com/d/msg/syzkaller-bugs/dRmkh2UYusY/l2a6Mg3FAQAJ
>
> Hi Phong,
>
> FYI, when testing patches with the usb-fuzzer instance, you need to
> provide the same kernel commit id as the one where the bug was
> triggered. Please see here for details:

https://github.com/google/syzkaller/blob/master/docs/syzbot.md#usb-bugs

>
> >
> > Signed-off-by: Phong Tran <tranmanphong@gmail.com>
> > ---
> >  drivers/usb/misc/appledisplay.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c
> > index ac92725458b5..3e3dfa5a3954 100644
> > --- a/drivers/usb/misc/appledisplay.c
> > +++ b/drivers/usb/misc/appledisplay.c
> > @@ -164,7 +164,8 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd)
> >                 0,
> >                 pdata->msgdata, 2,
> >                 ACD_USB_TIMEOUT);
> > -       brightness = pdata->msgdata[1];
> > +       if (retval >= 0)
> > +               brightness = pdata->msgdata[1];
> >         mutex_unlock(&pdata->sysfslock);
> >
> >         if (retval < 0)
> > --
> > 2.20.1
> >