macvtap: read vnet_hdr_size once
authorWillem de Bruijn <willemb@google.com>
Fri, 3 Feb 2017 23:20:49 +0000 (18:20 -0500)
committerDavid S. Miller <davem@davemloft.net>
Tue, 7 Feb 2017 03:41:27 +0000 (22:41 -0500)
commit837585a5375c38d40361cfe64e6fd11e1addb936
tree9acf1060c120551d70a9b31fc8075bf1d834eb98
parente1edab87faf6ca30cd137e0795bc73aa9a9a22ec
macvtap: read vnet_hdr_size once

When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
Data length is verified to be greater than or equal to expected header
length tun->vnet_hdr_sz before copying.

Macvtap functions read the value once, but unless READ_ONCE is used,
the compiler may ignore this and read multiple times. Enforce a single
read and locally cached value to avoid updates between test and use.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
drivers/net/macvtap.c