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Date: Sun, 28 Aug 2016 11:08:16 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] fix strdupa evaulating expression twice
On Sun, Aug 28, 2016 at 10:59:26AM +0000, Noam Meltzer wrote:
>
> From bf23b7b8fd39eaca6a05173eaf543e1bce3319ab Mon Sep 17 00:00:00 2001
> From: Noam Meltzer <tsnoam@...il.com>
> Date: Sun, 28 Aug 2016 13:53:24 +0300
> Subject: [PATCH] fix strdupa evaulating expression twice
>
> calling strdupa with va_arg as its expression caused unexpected
> behaviour. now the expression is evaulated only once.
> ---
> include/string.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/string.h b/include/string.h
> index ff9badb..976faaf 100644
> --- a/include/string.h
> +++ b/include/string.h
> @@ -85,7 +85,10 @@ size_t strlcpy (char *, const char *, size_t);
> #endif
>
> #ifdef _GNU_SOURCE
> -#define strdupa(x) strcpy(alloca(strlen(x)+1),x)
> +#define strdupa(x) (__extension__ ({ \
> + const char *__xval = x; \
> + strcpy(alloca(strlen(__xval)+1),__xval); \
> + }))
> int strverscmp (const char *, const char *);
> int strcasecmp_l (const char *, const char *, locale_t);
> int strncasecmp_l (const char *, const char *, size_t, locale_t);
The intent of the form as written is to be actual C (modulo use of
alloca) rather than "GNU C". Aside from that, strdupa is essentially
always-unsafe and should probably be removed or at least made into a
warning...
Rich
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