Re: [Intel-gfx] [PATCH v2] drm/i915: Fix invalid access to ACPI _DSM objects

[Takashi Iwai]

On Wed, 07 Apr 2021 18:34:46 +0200,
Ville Syrjälä wrote:
> 
> On Fri, Apr 02, 2021 at 10:23:17AM +0200, Takashi Iwai wrote:
> > intel_dsm_platform_mux_info() tries to parse the ACPI package data
> > from _DSM for the debug information, but it assumes the fixed format
> > without checking what values are stored in the elements actually.
> > When an unexpected value is returned from BIOS, it may lead to GPF or
> > NULL dereference, as reported recently.
> > 
> > Add the checks of the contents in the returned values and skip the
> > values for invalid cases.
> > 
> > v1->v2: Check the info contents before dereferencing, too
> > 
> > BugLink: http://bugzilla.opensuse.org/show_bug.cgi?id=1184074
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > ---
> >  drivers/gpu/drm/i915/display/intel_acpi.c | 22 ++++++++++++++++++++--
> >  1 file changed, 20 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_acpi.c b/drivers/gpu/drm/i915/display/intel_acpi.c
> > index e21fb14d5e07..833d0c1be4f1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_acpi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_acpi.c
> > @@ -84,13 +84,31 @@ static void intel_dsm_platform_mux_info(acpi_handle dhandle)
> >  		return;
> >  	}
> >  
> > +	if (!pkg->package.count) {
> > +		DRM_DEBUG_DRIVER("no connection in _DSM\n");
> > +		return;
> > +	}
> > +
> >  	connector_count = &pkg->package.elements[0];
> >  	DRM_DEBUG_DRIVER("MUX info connectors: %lld\n",
> >  		  (unsigned long long)connector_count->integer.value);
> >  	for (i = 1; i < pkg->package.count; i++) {
> >  		union acpi_object *obj = &pkg->package.elements[i];
> > -		union acpi_object *connector_id = &obj->package.elements[0];
> > -		union acpi_object *info = &obj->package.elements[1];
> > +		union acpi_object *connector_id;
> > +		union acpi_object *info;
> > +
> > +		if (obj->type != ACPI_TYPE_PACKAGE || obj->package.count < 2) {
> > +			DRM_DEBUG_DRIVER("Invalid object for MUX #%d\n", i);
> > +			continue;
> > +		}
> > +
> > +		connector_id = &obj->package.elements[0];
> 
> You don't want to check connector_id->type as well?

I added only the minimal checks that may lead to Oops.


Takashi

> 
> > +		info = &obj->package.elements[1];
> > +		if (info->type != ACPI_TYPE_BUFFER || info->buffer.length < 4) {
> > +			DRM_DEBUG_DRIVER("Invalid info for MUX obj #%d\n", i);
> > +			continue;
> > +		}
> > +
> >  		DRM_DEBUG_DRIVER("Connector id: 0x%016llx\n",
> >  			  (unsigned long long)connector_id->integer.value);
> >  		DRM_DEBUG_DRIVER("  port id: %s\n",
> > -- 
> > 2.26.2
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ville Syrjälä
> Intel
>