From 898e9a87dfc1b74d9459cc7079f7df66bc2ca07c Mon Sep 17 00:00:00 2001
From: Michael Kerrisk <mtk.manpages@gmail.com>
Date: Tue, 14 Dec 2004 18:25:46 +0000
Subject: [PATCH] Hello Joey,

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=205736

[[
This example contains the following line:

    if ((p = realloc (p, size)) == NULL)
       return NULL;

This is a very ill written code, since realloc returning
NULL do not deallocate the original memory block. Such a
statement has a potential to become significant memory
hole. I suggest to correct this example since:

1. It may trick naive programmers to write bad code
2. It may lead skeptic observers to the believe
   the whole Linux is written in a similar style.


Regards Jan Kuznik
]]

This guy is right on the money!

I've changed that example, so that the above code has been replaced by:

    char *np;

    ...


    if ((np = realloc (p, size)) == NULL) {
        free(p);
        return NULL;
    } else {
        p = np;
    }

Cheers,

Michael
---
 man3/printf.3 | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/man3/printf.3 b/man3/printf.3
index a5daac871..f96630a37 100644
--- a/man3/printf.3
+++ b/man3/printf.3
@@ -756,14 +756,17 @@ To allocate a sufficiently large string and print into it
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
+
 char *
 make_message(const char *fmt, ...) {
    /* Guess we need no more than 100 bytes. */
    int n, size = 100;
-   char *p;
+   char *p, *np;
    va_list ap;
+
    if ((p = malloc (size)) == NULL)
       return NULL;
+   
    while (1) {
       /* Try to print in the allocated space. */
       va_start(ap, fmt);
@@ -777,8 +780,12 @@ make_message(const char *fmt, ...) {
          size = n+1; /* precisely what is needed */
       else           /* glibc 2.0 */
          size *= 2;  /* twice the old size */
-      if ((p = realloc (p, size)) == NULL)
+      if ((np = realloc (p, size)) == NULL) {
+         free(p);
          return NULL;
+      } else {
+         p = np;
+      }
    }
 }
 .fi