malloc: Switch global_max_fast to uint8_t

MAX_FAST_SIZE is 160 at most, so a uint8_t is sufficient.  This makes
it harder to use memory corruption, by overwriting global_max_fast
with a large value, to fundamentally alter malloc behavior.

Reviewed-by: DJ Delorie <dj@redhat.com>

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 953183e..2a61c8b 100644 (file)
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1757,7 +1757,7 @@ typedef struct malloc_chunk *mfastbinptr;
 #define set_contiguous(M)      ((M)->flags &= ~NONCONTIGUOUS_BIT)
 
 /* Maximum size of memory handled in fastbins.  */
-static INTERNAL_SIZE_T global_max_fast;
+static uint8_t global_max_fast;
 
 /*
    Set value of max_fast.