linux-kernel - Re: [PATCH] netlink: don't copy over empty attribute data

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Message-Id: <20141026.220350.2098346782596904995.davem@davemloft.net>
Date:	Sun, 26 Oct 2014 22:03:50 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sasha.levin@...cle.com
Cc:	a.ryabinin@...sung.com, pablo@...filter.org, mschmidt@...hat.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] netlink: don't copy over empty attribute data

From: Sasha Levin <sasha.levin@...cle.com>
Date: Sun, 26 Oct 2014 19:32:42 -0400

> How so? GCC states clearly that you should *never* pass a NULL
> pointer there:
> 
> "The pointers passed to memmove (and similar functions in <string.h>) must
> be non-null even when nbytes==0" (https://gcc.gnu.org/gcc-4.9/porting_to.html).
> 
> Even if it doesn't dereference it, it can break somehow in a subtle way. Leaving
> the kernel code assuming that gcc (or any other compiler) would always behave
> the same in a situation that shouldn't occur.

Show me a legal way in which one could legally dereference the pointer
when length is zero, and I'll entertain this patch.
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