| From | Ben Hutchings <> | Date | Fri, 10 Mar 2017 11:46:10 +0000 | Subject | [PATCH 3.2 192/199] macvtap: read vnet_hdr_size once |
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3.2.87-rc1 review patch. If anyone has any objections, please let me know.
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From: Willem de Bruijn <willemb@google.com>
[ 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 <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> [bwh: BAckported to 3.2: - Use ACCESS_ONCE() instead of READ_ONCE() - Adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- drivers/net/macvtap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/net/macvtap.c +++ b/drivers/net/macvtap.c @@ -687,7 +687,7 @@ static ssize_t macvtap_get_user(struct 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 m 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;
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