netdev - Re: [PATCH v3 2/3] packet: fill the gap of TPACKET

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Date:	Mon, 16 Dec 2013 11:22:35 +0100
From:	Daniel Borkmann <dborkman@...hat.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	Atzm Watanabe <atzm@...atosphere.co.jp>, netdev@...r.kernel.org,
	Stephen Hemminger <stephen@...workplumber.org>,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH v3 2/3] packet: fill the gap of TPACKET_ALIGNMENT with
 zeros

On 12/16/2013 11:16 AM, David Laight wrote:
>>> +		memset(h.h2->tp_padding, 0,
>>> +		       hdrlen - offsetof(struct tpacket2_hdr, tp_padding));
>
> What is wrong with 'sizeof h.h2->tp_padding' ?
> The compiler will probably inline the memset into a couple of word
> sized writes of zero - probably not measurable.
> Not zeroing them might be leaking kernel memory contents (depends
> where the memory came from - might just be stale packet data).

The ring buffer memory we're operating on comes from mmap(2) btw.

> 	David
>
>
>
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