drm/vmwgfx: Validate command header size against SVGA_CMD_MAX_DATASIZE

This data originates from userspace and is used in buffer offset
calculations which could potentially overflow causing an out-of-bounds
access.

Fixes: 8ce75f8 ("drm/vmwgfx: Update device includes for DX device functionality")
Reported-by: Rohit Keshri <rkeshri@redhat.com>
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Reviewed-by: Maaz Mombasawala <maaz.mombasawala@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patch.msgid.link/20251021190128.13014-1-ian.forbes@broadcom.com

Author: en4bz

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -3668,6 +3668,11 @@ static int vmw_cmd_check(struct vmw_private *dev_priv,
 
 
 	cmd_id = header->id;
+	if (header->size > SVGA_CMD_MAX_DATASIZE) {
+		VMW_DEBUG_USER("SVGA3D command: %d is too big.\n",
+			       cmd_id + SVGA_3D_CMD_BASE);
+		return -E2BIG;
+	}
 	*size = header->size + sizeof(SVGA3dCmdHeader);
 
 	cmd_id -= SVGA_3D_CMD_BASE;