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Date: Thu, 21 Feb 2013 11:50:27 -0500
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] write strcasestr
On Thu, Feb 21, 2013 at 10:40:38AM -0500, Strake wrote:
> >From 6a228eaf8bc2b3830c56bd2c8caa2ffa44245531 Mon Sep 17 00:00:00 2001
> From: Strake <strake888@...il.com>
> Date: Thu, 21 Feb 2013 10:41:09 -0500
> Subject: [PATCH] write strcasestr
>
> ---
> src/string/strcasestr.c | 36 ++++++++++++++++++++++++++++++++----
> 1 file changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/src/string/strcasestr.c b/src/string/strcasestr.c
> index f1cb0e8..c67c606 100644
> --- a/src/string/strcasestr.c
> +++ b/src/string/strcasestr.c
> @@ -1,7 +1,35 @@
> +#include <stdlib.h>
> #include <string.h>
> +#include <wchar.h>
> +#include <stdio.h>
>
> -char *strcasestr(const char *h, const char *n)
> -{
> - //FIXME!
> - return strstr(h, n);
> +static void mbstolower (char *s) {
> + mbstate_t mbst;
> + wchar_t wx;
> +
> + while (*s) {
> + memset (&mbst, 0, sizeof (mbstate_t));
> + if (mbrtowc (&wx, s, MB_CUR_MAX, &mbst) < 0) break;
The return value of mbrtowc is unsigned so it can never be < 0.
> + wx = towlower (wx);
> + memset (&mbst, 0, sizeof (mbstate_t));
> + s += wcrtomb (s, wx, &mbst);
> + }
> +}
> +
> +char *strcasestr (const char *s, const char *t) {
> + char *x, *y, *z;
> +
> + x = strdup (s); if (!x) return 0;
> + y = strdup (t); if (!y) return 0;
This function does not have a way to report failure, so it cannot
fail; therefore, allocating storage is not an option. Returning zero
means the needle is not present in the haystack, not that the
implementation ran out of resources to look for it.
For a concrete example of where false negatives would be a security
problem, see Busybox's use of the function.
> + z = strstr (x, y);
> + if (z) s += z - x; else s = 0;
This logic is also incorrect. It assumes the length of the lowercase
characters is the same as the length of the corresponding uppercase
ones; this is in general false. Actually, this means your algorithm
has another serious security flaw: it may overrun the allocated
buffer when performing the case conversion.
Rich
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