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

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Date:	Mon, 16 Dec 2013 10:16:48 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Daniel Borkmann" <dborkman@...hat.com>,
	"Atzm Watanabe" <atzm@...atosphere.co.jp>
Cc:	<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

> > +		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).

	David



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