drm/i915: Fix invalid access to ACPI _DSM objects

BugLink: https://bugs.launchpad.net/bugs/1926489
commit b6a37a93c9ac3900987c79b726d0bb3699d8db4e upstream.

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@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210402082317.871-1-tiwai@suse.de
(cherry picked from commit 337d7a1621c7f02af867229990ac67c97da1b53a)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/gpu/drm/i915/display/intel_acpi.c b/drivers/gpu/drm/i915/display/intel_acpi.c
index 3456d33feb46aa52dd5e3095034886766ea5192c..ce8182bd0b55853fb5b3da497734f510b075c556 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_acpi.c
+++ b/drivers/gpu/drm/i915/display/intel_acpi.c
@@ -83,13 +83,31 @@ 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];
+               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",