Commit 837585a5 authored Feb 03, 2017 by Willem de Bruijn Committed by David S. Miller Feb 06, 2017

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>

parent e1edab87

drivers/net/macvtap.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -681,7 +681,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue q, struct msghdr m,
		size_t linear;

		if (q->flags & IFF_VNET_HDR) {
		vnet_hdr_len = q->vnet_hdr_sz;
		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);

		err = -EINVAL;
		if (len < vnet_hdr_len)
		@@ -820,7 +820,7 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,

		if (q->flags & IFF_VNET_HDR) {
		struct virtio_net_hdr vnet_hdr;
		vnet_hdr_len = q->vnet_hdr_sz;
		vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
		if (iov_iter_count(iter) < vnet_hdr_len)
		return -EINVAL;