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 <[email protected]> Suggested-by: Eric Dumazet <[email protected]> Acked-by: Eric Dumazet <[email protected]> Signed-off-by: David S. Miller <[email protected]>
redbrain17 · Feb 7, 2017 · 837585a · 837585a
1 parent e1edab8
commit 837585a
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
@@ -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;