netdev - [PATCH v3 1/3] packet: make aligned size of struct tpacket{2,3}

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Date:	Mon, 16 Dec 2013 17:12:03 +0900
From:	Atzm Watanabe <atzm@...atosphere.co.jp>
To:	netdev@...r.kernel.org
Cc:	"Stephen Hemminger" <stephen@...workplumber.org>,
	"Ben Hutchings" <bhutchings@...arflare.com>,
	"David Miller" <davem@...emloft.net>,
	"Daniel Borkmann" <dborkman@...hat.com>,
	"David Laight" <David.Laight@...LAB.COM>
Subject: [PATCH v3 1/3] packet: make aligned size of struct tpacket{2,3}_hdr clear

struct tpacket{2,3}_hdr is aligned to a multiple of TPACKET_ALIGNMENT.
We may add members to them until current aligned size without forcing
userspace to call getsockopt(..., PACKET_HDRLEN, ...).

Signed-off-by: Atzm Watanabe <atzm@...atosphere.co.jp>
---
 net/packet/af_packet.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 9d70f13..1c8b982 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1812,6 +1812,13 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	struct timespec ts;
 	__u32 ts_status;
 
+	/* struct tpacket{2,3}_hdr is aligned to a multiple of TPACKET_ALIGNMENT.
+	 * We may add members to them until current aligned size without forcing
+	 * userspace to call getsockopt(..., PACKET_HDRLEN, ...).
+	 */
+	BUILD_BUG_ON(TPACKET_ALIGN(sizeof(*h.h2)) != 32);
+	BUILD_BUG_ON(TPACKET_ALIGN(sizeof(*h.h3)) != 48);
+
 	if (skb->pkt_type == PACKET_LOOPBACK)
 		goto drop;
 
-- 
1.8.1.5

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