drm/hyperv: validate resolution_count and fix WIN8 fallback

A SYNTHVID_RESOLUTION_RESPONSE with resolution_count > 64 walks past
the supported_resolution[SYNTHVID_MAX_RESOLUTION_COUNT] array in the
parse loop. Bound resolution_count against the array size, folded
into the existing zero-check.

When the WIN10 resolution probe fails, the caller in
hyperv_connect_vsp() left hv->screen_*_max / preferred_* unpopulated,
which sets mode_config.max_width / max_height to 0 and makes
drm_internal_framebuffer_create() reject every userspace framebuffer
with -EINVAL. The pre-WIN10 branch had the same gap for
preferred_width / preferred_height. Use a single post-probe fallback
guarded by screen_width_max == 0 so both paths converge on the WIN8
defaults.

Signed-off-by: Berkant Koc <me@berkoc.com>
Assisted-by: Claude:claude-opus-4-7 berkoc-pipeline
Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic video device")
Cc: stable@vger.kernel.org # 5.14+
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Link: https://patch.msgid.link/6945b22419c7d404b4954a113de2ac9c900dba93.1779542874.git.me@berkoc.com

diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
index 051ecc52683217dcfb801187eec9c5ac90fc3313..c3d0ff229e3d030291266a69a59e791c23f17430 100644 (file)
--- a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
@@ -391,8 +391,11 @@ static int hyperv_get_supported_resolution(struct hv_device *hdev)
                return -ETIMEDOUT;
        }
 
-       if (msg->resolution_resp.resolution_count == 0) {
-               drm_err(dev, "No supported resolutions\n");
+       if (msg->resolution_resp.resolution_count == 0 ||
+           msg->resolution_resp.resolution_count >
+           SYNTHVID_MAX_RESOLUTION_COUNT) {
+               drm_err(dev, "Invalid resolution count: %d\n",
+                       msg->resolution_resp.resolution_count);
                return -ENODEV;
        }
 
@@ -508,9 +511,13 @@ int hyperv_connect_vsp(struct hv_device *hdev)
                ret = hyperv_get_supported_resolution(hdev);
                if (ret)
                        drm_err(dev, "Failed to get supported resolution from host, use default\n");
-       } else {
+       }
+
+       if (!hv->screen_width_max) {
                hv->screen_width_max = SYNTHVID_WIDTH_WIN8;
                hv->screen_height_max = SYNTHVID_HEIGHT_WIN8;
+               hv->preferred_width = SYNTHVID_WIDTH_WIN8;
+               hv->preferred_height = SYNTHVID_HEIGHT_WIN8;
        }
 
        hv->mmio_megabytes = hdev->channel->offermsg.offer.mmio_megabytes;