From 805bdc60879e0f5ca2054e74b6eeab255de76fbd Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Fri, 24 Aug 2018 05:18:20 -0400
Subject: [PATCH] add an extra sanity check for unallocated metadata

---
 malloc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/malloc.c b/malloc.c
index 3263371..8de5d76 100644
--- a/malloc.c
+++ b/malloc.c
@@ -276,6 +276,10 @@ static void *get_slab(struct size_class *c, size_t slab_size, struct slab_metada
 static struct slab_metadata *get_metadata(struct size_class *c, size_t slab_size, void *p) {
     size_t offset = (char *)p - (char *)c->class_region_start;
     size_t index = offset / slab_size;
+    // still caught without this check either as a read access violation or "double free"
+    if (index >= c->metadata_allocated) {
+        fatal_error("invalid free within a slab yet to be used");
+    }
     return c->slab_info + index;
 }