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Date: Tue, 19 Apr 2016 14:31:34 -0400 (EDT)
From: David Miller <davem@...emloft.net>
To: eric.dumazet@...il.com
Cc: roopa@...ulusnetworks.com, netdev@...r.kernel.org,
jhs@...atatu.com, tgraf@...g.ch, nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next v5] rtnetlink: add new RTM_GETSTATS message to
dump link stats
From: David Miller <davem@...emloft.net>
Date: Tue, 19 Apr 2016 01:03:16 -0400 (EDT)
> From: Eric Dumazet <eric.dumazet@...il.com>
> 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 <davem@...emloft.net>
---
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
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