full-disclosure - C99 Security Alert-Old-New-Who-Cares :)

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Message-ID: <200305301541.h4UFfce6006210@turing-police.cc.vt.edu>
From: Valdis.Kletnieks at vt.edu (Valdis.Kletnieks@...edu)
Subject: C99 Security Alert-Old-New-Who-Cares :) - (: 

On Fri, 30 May 2003 04:05:32 -0000, "democow ...." <democow8086@...mail.com>  said:

> char * strcpy(char * dest,const char *src)
> {
>         char *tmp = dest;
> 
>       [1]  while ((*dest++ = *src++) != '\0')
>                 /* nothing */;
>         return tmp;
> }

Kernighan & Ritchie, "The C Programming Language", had this in the first
edition - and correctly noted that this can be further optimized to:

             while (*dest++ = *src++);

eliminating a comparison to '\0'.  So not only is it insecure, but it's
inefficient, unless you have a *really* good optimizing compiler that can
tell that the comparison to null can be optimized away.  And yes, you
need a *good* optimizer that can see that comparing to a null byte is
a special case (for instance, you can't optimize   != '\n'  the same way).

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