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@stratosphere.co.jp>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 24675f06f4fd..4fd52181b6ce 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;