ipv6 addrconf: Implemented enhanced DAD (RFC7527)

Implemented RFC7527 Enhanced DAD.
IPv6 duplicate address detection can fail if there is some temporary
loopback of Ethernet frames. RFC7527 solves this by including a random
nonce in the NS messages used for DAD, and if an NS is received with the
same nonce it is assumed to be a looped back DAD probe and is ignored.
RFC7527 is enabled by default. Can be disabled by setting both of
conf/{all,interface}/enhanced_dad to zero.

Signed-off-by: Erik Nordmark <nordmark@arista.com>
Signed-off-by: Bob Gilligan <gilligan@arista.com>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 3 deletions

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index d8e671457d10..7ebac630d3c6 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -233,6 +233,7 @@ struct ndisc_options *ndisc_parse_options(const struct net_device *dev,
 		case ND_OPT_SOURCE_LL_ADDR:
 		case ND_OPT_TARGET_LL_ADDR:
 		case ND_OPT_MTU:
+		case ND_OPT_NONCE:
 		case ND_OPT_REDIRECT_HDR:
 			if (ndopts->nd_opt_array[nd_opt->nd_opt_type]) {
 				ND_PRINTK(2, warn,
@@ -568,7 +569,8 @@ static void ndisc_send_unsol_na(struct net_device *dev)
 }
 
 void ndisc_send_ns(struct net_device *dev, const struct in6_addr *solicit,
-		   const struct in6_addr *daddr, const struct in6_addr *saddr)
+		   const struct in6_addr *daddr, const struct in6_addr *saddr,
+		   u64 nonce)
 {
 	struct sk_buff *skb;
 	struct in6_addr addr_buf;
@@ -588,6 +590,8 @@ void ndisc_send_ns(struct net_device *dev, const struct in6_addr *solicit,
 	if (inc_opt)
 		optlen += ndisc_opt_addr_space(dev,
 					       NDISC_NEIGHBOUR_SOLICITATION);
+	if (nonce != 0)
+		optlen += 8;
 
 	skb = ndisc_alloc_skb(dev, sizeof(*msg) + optlen);
 	if (!skb)
@@ -605,6 +609,13 @@ void ndisc_send_ns(struct net_device *dev, const struct in6_addr *solicit,
 		ndisc_fill_addr_option(skb, ND_OPT_SOURCE_LL_ADDR,
 				       dev->dev_addr,
 				       NDISC_NEIGHBOUR_SOLICITATION);
+	if (nonce != 0) {
+		u8 *opt = skb_put(skb, 8);
+
+		opt[0] = ND_OPT_NONCE;
+		opt[1] = 8 >> 3;
+		memcpy(opt + 2, &nonce, 6);
+	}
 
 	ndisc_send_skb(skb, daddr, saddr);
 }
@@ -693,12 +704,12 @@ static void ndisc_solicit(struct neighbour *neigh, struct sk_buff *skb)
 				  "%s: trying to ucast probe in NUD_INVALID: %pI6\n",
 				  __func__, target);
 		}
-		ndisc_send_ns(dev, target, target, saddr);
+		ndisc_send_ns(dev, target, target, saddr, 0);
 	} else if ((probes -= NEIGH_VAR(neigh->parms, APP_PROBES)) < 0) {
 		neigh_app_ns(neigh);
 	} else {
 		addrconf_addr_solict_mult(target, &mcaddr);
-		ndisc_send_ns(dev, target, &mcaddr, saddr);
+		ndisc_send_ns(dev, target, &mcaddr, saddr, 0);
 	}
 }
 
@@ -742,6 +753,7 @@ static void ndisc_recv_ns(struct sk_buff *skb)
 	int dad = ipv6_addr_any(saddr);
 	bool inc;
 	int is_router = -1;
+	u64 nonce = 0;
 
 	if (skb->len < sizeof(struct nd_msg)) {
 		ND_PRINTK(2, warn, "NS: packet too short\n");
@@ -786,6 +798,8 @@ static void ndisc_recv_ns(struct sk_buff *skb)
 			return;
 		}
 	}
+	if (ndopts.nd_opts_nonce)
+		memcpy(&nonce, (u8 *)(ndopts.nd_opts_nonce + 1), 6);
 
 	inc = ipv6_addr_is_multicast(daddr);
 
@@ -794,6 +808,15 @@ static void ndisc_recv_ns(struct sk_buff *skb)
 have_ifp:
 		if (ifp->flags & (IFA_F_TENTATIVE|IFA_F_OPTIMISTIC)) {
 			if (dad) {
+				if (nonce != 0 && ifp->dad_nonce == nonce) {
+					u8 *np = (u8 *)&nonce;
+					/* Matching nonce if looped back */
+					ND_PRINTK(2, notice,
+						  "%s: IPv6 DAD loopback for address %pI6c nonce %pM ignored\n",
+						  ifp->idev->dev->name,
+						  &ifp->addr, np);
+					goto out;
+				}
 				/*
 				 * We are colliding with another node
 				 * who is doing DAD