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Date: Fri, 02 Aug 2002 02:29:00 -0000
Message-ID: <20020802092945.24679.qmail@md.dent.med.uni-muenchen.de>
From: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
To: libc-hacker@sources.redhat.com
In-reply-to: <20020802004635.Y20867@sunsite.ms.mff.cuni.cz> (message from
	Jakub Jelinek on Fri, 2 Aug 2002 00:46:35 +0200)
Subject: Re: [PATCH] xdr_array and calloc security fix
References:  <20020802004635.Y20867@sunsite.ms.mff.cuni.cz>
X-SW-Source: 2002-08/txt/msg00013.txt.bz2

Hi,

> +  /* size_t is unsigned so the behavior on overflow is defined.  */
> +  bytes = n * elem_size;
> +  if (bytes / elem_size != n) {
> +    MALLOC_FAILURE_ACTION;
> +    return 0;
> +  }

This is of course correct, but some (long) time ago I've measured that
the cost for the division is quite noticeable, for say, the very
common calloc(1, small_size).

I've given up on being able to do this fast _and_ portably.

Do we already have some system-specific mechanism to detect the rare
overflow case for a 32bit-multiplication without having to perform a
division?

Regards,
Wolfram.