Re: [PATCH] drivers: tty: vt: vt.c: fix NULL dereference crash

From: Hassan Shahbazi
Date: Sat Mar 13 2021 - 04:13:34 EST


On Fri, Mar 12, 2021 at 09:33:37AM +0100, Greg KH wrote:
> On Sun, Mar 07, 2021 at 12:56:43PM +0200, Hassan Shahbazi wrote:
> > Fix a NULL deference crash on hiding the cursor.
> >
> > Reported by: syzbot
> > https://syzkaller.appspot.com/bug?id=defb47bf56e1c14d5687280c7bb91ce7b608b94b
> >
> > Signed-off-by: Hassan Shahbazi <h.shahbazi.git@xxxxxxxxx>
> > ---
> > drivers/tty/vt/vt.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> > index 284b07224c55..8c3e83c81341 100644
> > --- a/drivers/tty/vt/vt.c
> > +++ b/drivers/tty/vt/vt.c
> > @@ -904,7 +904,9 @@ static void hide_cursor(struct vc_data *vc)
> > if (vc_is_sel(vc))
> > clear_selection();
> >
> > - vc->vc_sw->con_cursor(vc, CM_ERASE);
> > + if (vc->vc_sw)
> > + vc->vc_sw->con_cursor(vc, CM_ERASE);
> > +
> > hide_softcursor(vc);
> > }
> >
> > --
> > 2.26.2
> >
>
> Are you sure this actually fixes the problem? How did you test it? Did
> syzbot test this?
>
> I had a few reports of this patch _not_ solving the problem, so getting
> confirmation of this would be good.
>
> thanks,
>
> greg k-h

Unfortunately, it seems the patch has not fixed the bug. I drop this
patch and will continue working on a newer one.

Thanks for the feedback,
Hassan Shahbazi