From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next v5] rtnetlink: add new RTM_GETSTATS message to dump link stats Date: Tue, 19 Apr 2016 14:31:34 -0400 (EDT) Message-ID: <20160419.143134.2014460805657420897.davem@davemloft.net> References: <20160418.234137.26692086759328024.davem@davemloft.net> <1461040324.10638.159.camel@edumazet-glaptop3.roam.corp.google.com> <20160419.010316.1863885429013017239.davem@davemloft.net> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: roopa@cumulusnetworks.com, netdev@vger.kernel.org, jhs@mojatatu.com, tgraf@suug.ch, nicolas.dichtel@6wind.com To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:36575 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754830AbcDSSbg (ORCPT ); Tue, 19 Apr 2016 14:31:36 -0400 In-Reply-To: <20160419.010316.1863885429013017239.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: From: David Miller Date: Tue, 19 Apr 2016 01:03:16 -0400 (EDT) > From: Eric Dumazet > Date: Mon, 18 Apr 2016 21:32:04 -0700 > >> On Mon, 2016-04-18 at 23:41 -0400, David Miller wrote: >>> >>> + /* Add a zero length NOP attribute so that the nla_data() >>> + * of the IFLA_STATS64 will be 64-bit aligned. >>> + */ >>> +#ifndef HAVE_EFFICIENT_UNALIGNED_ACCESS >>> + attr = nla_reserve(skb, IFLA_PAD, 0); >>> + if (!attr) >>> + return -EMSGSIZE; >>> +#endif >> >> You must do this only if current skb->data alignment is not correct. > > I'll put an assertion there if it makes you happy. :-) Actually, you are right, as usual. Here is the final patch I'm about to push out, thanks a lot Eric. Roopa, please adjust your GETSTATS patch as needed (I think you need to adjust the SELinux table entry as well) and we can integrate that too. ==================== [PATCH] net: Align IFLA_STATS64 attributes properly on architectures that need it. Since the nlattr header is 4 bytes in size, it can cause the netlink attribute payload to not be 8-byte aligned. This is particularly troublesome for IFLA_STATS64 which contains 64-bit statistic values. Solve this by creating a dummy IFLA_PAD attribute which has a payload which is zero bytes in size. When HAVE_EFFICIENT_UNALIGNED_ACCESS is false, we insert an IFLA_PAD attribute into the netlink response when necessary such that the IFLA_STATS64 payload will be properly aligned. With help and suggestions from Eric Dumazet. Signed-off-by: David S. Miller --- include/uapi/linux/if_link.h | 1 + net/core/rtnetlink.c | 19 +++++++++++++++++++ 2 files changed, 20 insertions(+) diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h index bb3a90b..5ffdcb3 100644 --- a/include/uapi/linux/if_link.h +++ b/include/uapi/linux/if_link.h @@ -155,6 +155,7 @@ enum { IFLA_PROTO_DOWN, IFLA_GSO_MAX_SEGS, IFLA_GSO_MAX_SIZE, + IFLA_PAD, __IFLA_MAX }; diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index a7a3d34..198ca2c 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -878,6 +878,9 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev, + nla_total_size(IFNAMSIZ) /* IFLA_QDISC */ + nla_total_size(sizeof(struct rtnl_link_ifmap)) + nla_total_size(sizeof(struct rtnl_link_stats)) +#ifndef HAVE_EFFICIENT_UNALIGNED_ACCESS + + nla_total_size(0) /* IFLA_PAD */ +#endif + nla_total_size(sizeof(struct rtnl_link_stats64)) + nla_total_size(MAX_ADDR_LEN) /* IFLA_ADDRESS */ + nla_total_size(MAX_ADDR_LEN) /* IFLA_BROADCAST */ @@ -1052,6 +1055,22 @@ static noinline_for_stack int rtnl_fill_stats(struct sk_buff *skb, struct rtnl_link_stats64 *sp; struct nlattr *attr; +#ifndef HAVE_EFFICIENT_UNALIGNED_ACCESS + /* IF necessary, add a zero length NOP attribute so that the + * nla_data() of the IFLA_STATS64 will be 64-bit aligned. + * + * The nlattr header is 4 bytes in size, that's why we test + * if the skb->data _is_ aligned. This NOP attribute, plus + * nlattr header for IFLA_STATS64, will make nla_data() 8-byte + * aligned. + */ + if (IS_ALIGNED((unsigned long)skb->data, 8)) { + attr = nla_reserve(skb, IFLA_PAD, 0); + if (!attr) + return -EMSGSIZE; + } +#endif + attr = nla_reserve(skb, IFLA_STATS64, sizeof(struct rtnl_link_stats64)); if (!attr) -- 2.4.1