very cheap double-free checks in malloc

diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index 3c08c41..a4eefda 100644 (file)
--- a/src/malloc/malloc.c
+++ b/src/malloc/malloc.c
@@ -393,6 +393,8 @@ void *realloc(void *p, size_t n)
                char *base = (char *)self - extra;
                size_t oldlen = n0 + extra;
                size_t newlen = n + extra;
+               /* Crash on realloc of freed chunk */
+               if ((uintptr_t)base < mal.brk) *(char *)0=0;
                if (newlen < PAGE_SIZE && (new = malloc(n))) {
                        memcpy(new, p, n-OVERHEAD);
                        free(p);
@@ -454,6 +456,8 @@ void free(void *p)
                size_t extra = self->data[-1];
                char *base = (char *)self - extra;
                size_t len = CHUNK_SIZE(self) + extra;
+               /* Crash on double free */
+               if ((uintptr_t)base < mal.brk) *(char *)0=0;
                __munmap(base, len);
                return;
        }