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Commit 18402843 authored by David S. Miller's avatar David S. Miller
Browse files

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: default avatarDavid S. Miller <davem@davemloft.net>
parent b67d1df5

include/uapi/linux/if_link.h

+1 −0
Original line number Diff line number Diff line
@@ -155,6 +155,7 @@ enum { 
	IFLA_PROTO_DOWN,

	IFLA_GSO_MAX_SEGS,

	IFLA_GSO_MAX_SIZE,

	IFLA_PAD,

	__IFLA_MAX

};

net/core/rtnetlink.c

+19 −0
Original line number Diff line number Diff line
@@ -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)