[subset] Check instruction offsets in glyph to ensure they are in bounds.

src/hb-ot-glyf-table.hh

@@ -433,9 +433,23 @@ struct glyf
       else
       {
         unsigned int instruction_length_offset = start_offset + GlyphHeader::static_size + 2 * num_contours;
+	if (unlikely (instruction_length_offset + 2 > end_offset))
+	{
+	  DEBUG_MSG(SUBSET, nullptr, "Glyph size is too short, missing field instructionLength.");
+	  return false;
+	}
+
         const HBUINT16 &instruction_length = StructAtOffset<HBUINT16> (glyf_table, instruction_length_offset);
-        *instruction_start = instruction_length_offset + 2;
-        *instruction_end = *instruction_start + (uint16_t) instruction_length;
+	unsigned int start = instruction_length_offset + 2;
+	unsigned int end = start + (uint16_t) instruction_length;
+	if (unlikely (end > end_offset)) // Out of bounds of the current glyph
+	{
+	  DEBUG_MSG(SUBSET, nullptr, "The instructions array overruns the glyph's boundaries.");
+	  return false;
+	}
+
+	*instruction_start = start;
+        *instruction_end = end;
       }
       return true;
     }

test/api/test-subset-glyf.c

@@ -171,6 +171,36 @@ test_subset_glyf_strip_hints_composite (void)
   hb_face_destroy (face_components);
 }
 
+static void
+test_subset_glyf_strip_hints_invalid (void)
+{
+  hb_face_t *face = hb_subset_test_open_font ("fonts/oom-ccc61c92d589f895174cdef6ff2e3b20e9999a1a");
+
+  hb_set_t *codepoints = hb_set_create();
+  const hb_codepoint_t text[] =
+      {
+        'A', 'B', 'C', 'D', 'E', 'X', 'Y', 'Z', '1', '2',
+        '3', '@', '_', '%', '&', ')', '*', '$', '!'
+      };
+  int i;
+  for (i = 0; i < sizeof (text) / sizeof (hb_codepoint_t); i++)
+  {
+    hb_set_add (codepoints, text[i]);
+    // hb_set_add (codepoints_drop_hints, text[i]);
+  }
+
+  hb_subset_input_t *input = hb_subset_test_create_input (codepoints);
+  *hb_subset_input_drop_hints(input) = true;
+  hb_set_destroy (codepoints);
+
+  hb_face_t *face_subset = hb_subset_test_create_subset (face, input);
+  g_assert (face_subset);
+  g_assert (face_subset == hb_face_get_empty ());
+
+  hb_face_destroy (face_subset);
+  hb_face_destroy (face);
+}
+
 // TODO(grieger): test for long loca generation.
 
 int
@@ -182,6 +212,7 @@ main (int argc, char **argv)
   hb_test_add (test_subset_glyf);
   hb_test_add (test_subset_glyf_strip_hints_simple);
   hb_test_add (test_subset_glyf_strip_hints_composite);
+  hb_test_add (test_subset_glyf_strip_hints_invalid);
   hb_test_add (test_subset_glyf_with_components);
 
   return hb_test_run();