Re: [RFC 2/2] Make misuse of get_pathname() buffers detectable by valgrind

From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: Nov 16, 2011, 14:18 UTC
Message-ID: <CACsJy8BK3zvxA5mpC+3UvYMe20X6iFWJ7JL+VH6fr-Xstw2usg@mail.gmail.com>
In-Reply-To: <1317097687-11098-3-git-send-email-mhagger@alum.mit.edu>

On Tue, Sep 27, 2011 at 11:28 AM, Michael Haggerty <mhagger@alum.mit.edu> wrote:

Show 18 quoted lines

> +#ifdef VALGRIND
> +       static char *pathname_array[PATHNAME_BUFFER_COUNT];
> +       index = (index + 1) & (PATHNAME_BUFFER_COUNT - 1);
> +       if (pathname_array[index]) {
> +               /*
> +                * In a correct program, this will have no effect, but
> +                * *if* somebody erroneously uses this buffer after it
> +                * has been freed, it gives more of a chance that the
> +                * error will be detected even if valgrind is not
> +                * running:
> +                */
> +               strcpy(pathname_array[index], buggy_path);
> +
> +               free(pathname_array[index]);
> +       }
> +       pathname_array[index] = xmalloc(PATH_MAX);
> +       return pathname_array[index];
> +#else

Not sure if it works (just read man pages, haven't tried anything) I'm thinking to use mmap() with MAP_ANONYMOUS instead of xmalloc(), then mprotect() instead of free() to remove read access from that area. Any access after that should be caught. Leaking may not be severe for git_path(), hopefully.

-- 
Duy