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net: Align IFLA_STATS64 attributes properly on architectures that need it.

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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@davemloft.net>
This commit is contained in:
David S. Miller 2016-04-19 14:30:10 -04:00
parent b67d1df5ad
commit 18402843bf
2 changed files with 20 additions and 0 deletions
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1
include/uapi/linux/if_link.h
View File

@ -155,6 +155,7 @@ enum {
IFLA_PROTO_DOWN,
IFLA_GSO_MAX_SEGS,
IFLA_GSO_MAX_SIZE,
IFLA_PAD,
__IFLA_MAX
};

19
net/core/rtnetlink.c
View File

@ -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)