To: linux-kernel@vger.kernel.org
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From: daw@cs.berkeley.edu (David Wagner)
Newsgroups: isaac.lists.linux-kernel
Subject: Re: [RFC][PATCH] mm: Remove ZERO_SIZE_PTR.
Date: Fri, 26 Feb 2010 18:23:06 +0000 (UTC)
Organization: University of California, Berkeley
Message-ID: <hm93ia$15p$1@taverner.cs.berkeley.edu>
References: <201002260635.o1Q6ZYET040848@www262.sakura.ne.jp> <20100226155618.8D9E.A69D9226@jp.fujitsu.com> <201002260838.o1Q8cfr2068194@www262.sakura.ne.jp>
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Originator: daw@taverner.cs.berkeley.edu (David Wagner)
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Tetsuo Handa  wrote:
>This patch simplifies error checks of both callers/callees from
>
>	((unsigned long)(x) <= (unsigned long) 16)
>
>to
>
>	!(x)

I don't follow.  If you want to avoid integer overflow, the caller
of kmalloc() must check to make sure that the arithmetic operations
it performs do not overflow.  That's true whether or not your patch
is accepted.  An integer overflow in an arithmetic operation can yield
a non-zero value, so checking "!(x)" does not guarantee that there was
no integer overflow involved in the computation of x.
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