ipv6 addrconf: add accept_dad sysctl to control DAD operation.

- If 0, disable DAD.
- If 1, perform DAD (default).
- If >1, perform DAD and disable IPv6 operation if DAD for MAC-based
  link-local address has been failed (RFC4862 5.4.5).

We do not follow RFC4862 by default.  Refer to the netdev thread entitled
"Linux IPv6 DAD not full conform to RFC 4862 ?"
	http://www.spinics.net/lists/netdev/msg52027.htmlSigned-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

Documentation/networking/ip-sysctl.txt

@@ -1029,6 +1029,13 @@ disable_ipv6 - BOOLEAN
 	Disable IPv6 operation.
 	Default: FALSE (enable IPv6 operation)
 
+accept_dad - INTEGER
+	Whether to accept DAD (Duplicate Address Detection).
+	0: Disable DAD
+	1: Enable DAD (default)
+	2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
+	   link-local address has been found.
+
 icmp/*:
 ratelimit - INTEGER
 	Limit the maximal rates for sending ICMPv6 packets.

include/linux/ipv6.h

@@ -164,6 +164,7 @@ struct ipv6_devconf {
 	__s32		mc_forwarding;
 #endif
 	__s32		disable_ipv6;
+	__s32		accept_dad;
 	void		*sysctl;
 };
 
@@ -196,6 +197,7 @@ enum {
 	DEVCONF_ACCEPT_SOURCE_ROUTE,
 	DEVCONF_MC_FORWARDING,
 	DEVCONF_DISABLE_IPV6,
+	DEVCONF_ACCEPT_DAD,
 	DEVCONF_MAX
 };
 

net/ipv6/addrconf.c

@@ -119,6 +119,7 @@ static void ipv6_regen_rndid(unsigned long data);
 static int desync_factor = MAX_DESYNC_FACTOR * HZ;
 #endif
 
+static int ipv6_generate_eui64(u8 *eui, struct net_device *dev);
 static int ipv6_count_addresses(struct inet6_dev *idev);
 
 /*
@@ -184,6 +185,7 @@ struct ipv6_devconf ipv6_devconf __read_mostly = {
 	.proxy_ndp		= 0,
 	.accept_source_route	= 0,	/* we do not accept RH0 by default. */
 	.disable_ipv6		= 0,
+	.accept_dad		= 1,
 };
 
 static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
@@ -217,6 +219,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
 	.proxy_ndp		= 0,
 	.accept_source_route	= 0,	/* we do not accept RH0 by default. */
 	.disable_ipv6		= 0,
+	.accept_dad		= 1,
 };
 
 /* IPv6 Wildcard Address and Loopback Address defined by RFC2553 */
@@ -380,6 +383,9 @@ static struct inet6_dev * ipv6_add_dev(struct net_device *dev)
 	 */
 	in6_dev_hold(ndev);
 
+	if (dev->flags & (IFF_NOARP | IFF_LOOPBACK))
+		ndev->cnf.accept_dad = -1;
+
 #if defined(CONFIG_IPV6_SIT) || defined(CONFIG_IPV6_SIT_MODULE)
 	if (dev->type == ARPHRD_SIT && (dev->priv_flags & IFF_ISATAP)) {
 		printk(KERN_INFO
@@ -1421,6 +1427,20 @@ static void addrconf_dad_stop(struct inet6_ifaddr *ifp)
 
 void addrconf_dad_failure(struct inet6_ifaddr *ifp)
 {
+	struct inet6_dev *idev = ifp->idev;
+	if (idev->cnf.accept_dad > 1 && !idev->cnf.disable_ipv6) {
+		struct in6_addr addr;
+
+		addr.s6_addr32[0] = htonl(0xfe800000);
+		addr.s6_addr32[1] = 0;
+
+		if (!ipv6_generate_eui64(addr.s6_addr + 8, idev->dev) &&
+		    ipv6_addr_equal(&ifp->addr, &addr)) {
+			/* DAD failed for link-local based on MAC address */
+			idev->cnf.disable_ipv6 = 1;
+		}
+	}
+
 	if (net_ratelimit())
 		printk(KERN_INFO "%s: duplicate address detected!\n", ifp->idev->dev->name);
 	addrconf_dad_stop(ifp);
@@ -2753,6 +2773,7 @@ static void addrconf_dad_start(struct inet6_ifaddr *ifp, u32 flags)
 	spin_lock_bh(&ifp->lock);
 
 	if (dev->flags&(IFF_NOARP|IFF_LOOPBACK) ||
+	    idev->cnf.accept_dad < 1 ||
 	    !(ifp->flags&IFA_F_TENTATIVE) ||
 	    ifp->flags & IFA_F_NODAD) {
 		ifp->flags &= ~(IFA_F_TENTATIVE|IFA_F_OPTIMISTIC);
@@ -2800,6 +2821,11 @@ static void addrconf_dad_timer(unsigned long data)
 		read_unlock_bh(&idev->lock);
 		goto out;
 	}
+	if (idev->cnf.accept_dad > 1 && idev->cnf.disable_ipv6) {
+		read_unlock_bh(&idev->lock);
+		addrconf_dad_failure(ifp);
+		return;
+	}
 	spin_lock_bh(&ifp->lock);
 	if (ifp->probes == 0) {
 		/*
@@ -3660,6 +3686,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	array[DEVCONF_MC_FORWARDING] = cnf->mc_forwarding;
 #endif
 	array[DEVCONF_DISABLE_IPV6] = cnf->disable_ipv6;
+	array[DEVCONF_ACCEPT_DAD] = cnf->accept_dad;
 }
 
 static inline size_t inet6_if_nlmsg_size(void)
@@ -4226,6 +4253,14 @@ static struct addrconf_sysctl_table
 			.mode		=	0644,
 			.proc_handler	=	&proc_dointvec,
 		},
+		{
+			.ctl_name	=	CTL_UNNUMBERED,
+			.procname	=	"accept_dad",
+			.data		=	&ipv6_devconf.accept_dad,
+			.maxlen		=	sizeof(int),
+			.mode		=	0644,
+			.proc_handler	=	&proc_dointvec,
+		},
 		{
 			.ctl_name	=	0,	/* sentinel */
 		}