preproc: fix heap memory overflow CVE-2023-31722

paramlen has heap memory of length nparam+1. The value of variable i
may be greater than nparam+1, causing heap memory overflow. Therefore,
i and nparam+1 needs to be determined in the loop.

Fixes: https://bugzilla.nasm.us/show_bug.cgi?id=3392857#c1
Fixes: #83
Signed-off-by: H. Peter Anvin (Intel) <[email protected]>

Author: hongjinghao

asm/preproc.c

@@ -7245,7 +7245,7 @@ static int expand_mmacro(Token * tline)
      */
     nasm_newn(paramlen, nparam+1);
 
-    for (i = 1; (t = params[i]); i++) {
+    for (i = 1; i < nparam+1 && (t = params[i]); i++) {
         bool braced = false;
         int brace = 0;
         int white = 0;

nasmlib/alloc.c

@@ -74,8 +74,10 @@ void *nasm_realloc(void *q, size_t size)
 
 void nasm_free(void *q)
 {
-    if (q)
+    if (q){
         free(q);
+	q = NULL;
+    }
 }
 
 char *nasm_strdup(const char *s)