From 43df37dbc66707afbf8a93cc9f6430b31be3931e Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Fri, 3 Feb 2017 18:20:49 -0500 Subject: [PATCH 1/1] macvtap: read vnet_hdr_size once [ Upstream commit 837585a5375c38d40361cfe64e6fd11e1addb936 ] 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 Suggested-by: Eric Dumazet Acked-by: Eric Dumazet Signed-off-by: David S. Miller [bwh: BAckported to 3.2: - Use ACCESS_ONCE() instead of READ_ONCE() - Adjust context] Signed-off-by: Ben Hutchings --- drivers/net/macvtap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c index 2fcdedefce42..1c3db94e4237 100644 --- a/drivers/net/macvtap.c +++ b/drivers/net/macvtap.c @@ -687,7 +687,7 @@ 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 = ACCESS_ONCE(q->vnet_hdr_sz); err = -EINVAL; if (len < vnet_hdr_len) @@ -817,7 +817,7 @@ 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 = ACCESS_ONCE(q->vnet_hdr_sz); if ((len -= vnet_hdr_len) < 0) return -EINVAL; -- 2.39.2