Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936449AbdCJMSP (ORCPT ); Fri, 10 Mar 2017 07:18:15 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:45178 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936555AbdCJMSL (ORCPT ); Fri, 10 Mar 2017 07:18:11 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Willem de Bruijn" , "Eric Dumazet" , "David S. Miller" Date: Fri, 10 Mar 2017 11:46:23 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 359/370] macvtap: read vnet_hdr_size once In-Reply-To: X-SA-Exim-Connect-IP: 82.70.136.246 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1587 Lines: 48 3.16.42-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Willem de Bruijn [ 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 3.16: - 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(-) --- a/drivers/net/macvtap.c +++ b/drivers/net/macvtap.c @@ -657,7 +657,7 @@ 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) @@ -793,7 +793,7 @@ 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;