Merge pull request 'Check whether data is parsable by 'imagecreatefromstring' in jimIcon.' (#7) from wn/tt-rss:jimIcon-imagecreatefromstring into master

Reviewed-on: https://git.tt-rss.org/fox/tt-rss/pulls/7

lib/jimIcon.php

@@ -104,12 +104,12 @@ class jimIcon {
                 }
 
                 // See if we can parse it (might be PNG format here)
-                $i = @imagecreatefromstring($data);
-
-                if ($i) {
+                if (self::has_parsable_image_type($data)) {
+                        if ($i = @imagecreatefromstring($data)) {
                                 imagesavealpha($i, true);
                                 return $i;
                         }
+                }
 
                 // Must be a BMP.  Parse it ourselves.
                 $img = imagecreatetruecolor($e["width"], $e["height"]);
@@ -267,5 +267,12 @@ class jimIcon {
                 }
                 return $img;
         }
+
+        // Checks whether the data is a type parsable by imagecreatefromstring()
+        private function has_parsable_image_type($image_data) {
+                $size = getimagesizefromstring($image_data);
+                return $size && in_array($size[2],
+                        [IMAGETYPE_JPEG, IMAGETYPE_PNG, IMAGETYPE_GIF, IMAGETYPE_BMP, IMAGETYPE_WBMP, IMAGETYPE_WEBP]);
+        }
 }
 ?>