回覆: [PATCH] drm/dp_mst: Avoid NULL pointer dereference

[Lin, Wayne]

[AMD Public Use]



> -----原始郵件-----
> 寄件者: Lyude Paul <lyude at redhat.com>
> 寄件日期: Saturday, January 4, 2020 4:35 AM
> 收件者: Lin, Wayne <Wayne.Lin at amd.com>; dri-
> devel at lists.freedesktop.org; amd-gfx at lists.freedesktop.org
> 副本: Kazlauskas, Nicholas <Nicholas.Kazlauskas at amd.com>; Wentland,
> Harry <Harry.Wentland at amd.com>; Lipski, Mikita <Mikita.Lipski at amd.com>;
> Zuo, Jerry <Jerry.Zuo at amd.com>; stable at vger.kernel.org
> 主旨: Re: [PATCH] drm/dp_mst: Avoid NULL pointer dereference
> 
> Back from the holidays!
> 
> Reviewed-by: Lyude Paul <lyude at redhat.com>
> 
> Do you need me to push this to drm-misc?
> 
Thanks for your time!
And yes, please help to push this to drm-misc.

> On Thu, 2019-12-26 at 10:31 +0800, Wayne Lin wrote:
> > [Why]
> > Found kernel NULL pointer dereference under the below situation:
> >
> > 	src — HDMI_Monitor   src — HDMI_Monitor
> > e.g.:	    \            =>
> > 	     MSTB — MSTB     (unplug) MSTB — MSTB
> >
> > When display 1 HDMI and 2 DP daisy chain monitors, unplugging the dp
> > cable connected to source causes kernel NULL pointer dereference at
> > drm_dp_mst_atomic_check_bw_limit(). When calculating pbn_limit, if
> > branch is null, accessing "&branch->ports" causes the problem.
> >
> > [How]
> > Judge branch is null or not at the beginning. If it is null, return 0.
> >
> > Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
> > Cc: stable at vger.kernel.org
> > ---
> >  drivers/gpu/drm/drm_dp_mst_topology.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 7d2d31eaf003..a6473e3ab448 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -4707,6 +4707,9 @@ int drm_dp_mst_atomic_check_bw_limit(struct
> > drm_dp_mst_branch *branch,
> >  	struct drm_dp_vcpi_allocation *vcpi;
> >  	int pbn_limit = 0, pbn_used = 0;
> >
> > +	if (!branch)
> > +		return 0;
> > +
> >  	list_for_each_entry(port, &branch->ports, next) {
> >  		if (port->mstb)
> >  			if (drm_dp_mst_atomic_check_bw_limit(port->mstb,
> > mst_state))
> --
> Cheers,
> 	Lyude Paul
--
Best regards,
Wayne Lin