ipv6: addrconf: implement address generation modes

This patch introduces a possibility for userspace to set various (so far
two) modes of generating addresses. This is useful for example for
NetworkManager because it can set the mode to NONE and take care of link
local addresses itself. That allow it to have the interface up,
monitoring carrier but still don't have any addresses on it.

One more use-case by Dan Williams:
<quote>
WWAN devices often have their LL address provided by the firmware of the
device, which sometimes refuses to respond to incorrect LL addresses
when doing DHCPv6 or IPv6 ND.  The kernel cannot generate the correct LL
address for two reasons:

1) WWAN pseudo-ethernet interfaces often construct a fake MAC address,
or read a meaningless MAC address from the firmware.  Thus the EUI64 and
the IPv6LL address the kernel assigns will be wrong.  The real LL
address is often retrieved from the firmware with AT or proprietary
commands.

2) WWAN PPP interfaces receive their LL address from IPV6CP, not from
kernel assignments.  Only after IPV6CP has completed do we know the LL
address of the PPP interface and its peer.  But the kernel has already
assigned an incorrect LL address to the interface.

So being able to suppress the kernel LL address generation and assign
the one retrieved from the firmware is less complicated and more robust.
</quote>

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/if_inet6.h

@@ -205,6 +205,7 @@ struct inet6_dev {
 	struct timer_list	rs_timer;
 	__u8			rs_probes;
 
+	__u8			addr_gen_mode;
 	unsigned long		tstamp; /* ipv6InterfaceTable update timestamp */
 	struct rcu_head		rcu;
 };

include/uapi/linux/if_link.h

@@ -204,11 +204,17 @@ enum {
 	IFLA_INET6_CACHEINFO,	/* time values and max reasm size */
 	IFLA_INET6_ICMP6STATS,	/* statistics (icmpv6)		*/
 	IFLA_INET6_TOKEN,	/* device token			*/
+	IFLA_INET6_ADDR_GEN_MODE, /* implicit address generator mode */
 	__IFLA_INET6_MAX
 };
 
 #define IFLA_INET6_MAX	(__IFLA_INET6_MAX - 1)
 
+enum in6_addr_gen_mode {
+	IN6_ADDR_GEN_MODE_EUI64,
+	IN6_ADDR_GEN_MODE_NONE,
+};
+
 enum {
 	BRIDGE_MODE_UNSPEC,
 	BRIDGE_MODE_HAIRPIN,

net/ipv6/addrconf.c

@@ -2730,9 +2730,25 @@ static void addrconf_add_linklocal(struct inet6_dev *idev, const struct in6_addr
 	}
 }
 
+static void addrconf_addr_gen(struct inet6_dev *idev, bool prefix_route)
+{
+	if (idev->addr_gen_mode == IN6_ADDR_GEN_MODE_EUI64) {
+		struct in6_addr addr;
+
+		ipv6_addr_set(&addr,  htonl(0xFE800000), 0, 0, 0);
+		/* addrconf_add_linklocal also adds a prefix_route and we
+		 * only need to care about prefix routes if ipv6_generate_eui64
+		 * couldn't generate one.
+		 */
+		if (ipv6_generate_eui64(addr.s6_addr + 8, idev->dev) == 0)
+			addrconf_add_linklocal(idev, &addr);
+		else if (prefix_route)
+			addrconf_prefix_route(&addr, 64, idev->dev, 0, 0);
+	}
+}
+
 static void addrconf_dev_config(struct net_device *dev)
 {
-	struct in6_addr addr;
 	struct inet6_dev *idev;
 
 	ASSERT_RTNL();
@@ -2753,11 +2769,7 @@ static void addrconf_dev_config(struct net_device *dev)
 	if (IS_ERR(idev))
 		return;
 
-	memset(&addr, 0, sizeof(struct in6_addr));
-	addr.s6_addr32[0] = htonl(0xFE800000);
-
-	if (ipv6_generate_eui64(addr.s6_addr + 8, dev) == 0)
-		addrconf_add_linklocal(idev, &addr);
+	addrconf_addr_gen(idev, false);
 }
 
 #if IS_ENABLED(CONFIG_IPV6_SIT)
@@ -2779,11 +2791,7 @@ static void addrconf_sit_config(struct net_device *dev)
 	}
 
 	if (dev->priv_flags & IFF_ISATAP) {
-		struct in6_addr addr;
-
-		ipv6_addr_set(&addr,  htonl(0xFE800000), 0, 0, 0);
-		if (!ipv6_generate_eui64(addr.s6_addr + 8, dev))
-			addrconf_add_linklocal(idev, &addr);
+		addrconf_addr_gen(idev, false);
 		return;
 	}
 
@@ -2798,7 +2806,6 @@ static void addrconf_sit_config(struct net_device *dev)
 static void addrconf_gre_config(struct net_device *dev)
 {
 	struct inet6_dev *idev;
-	struct in6_addr addr;
 
 	ASSERT_RTNL();
 
@@ -2807,11 +2814,7 @@ static void addrconf_gre_config(struct net_device *dev)
 		return;
 	}
 
-	ipv6_addr_set(&addr,  htonl(0xFE800000), 0, 0, 0);
-	if (!ipv6_generate_eui64(addr.s6_addr + 8, dev))
-		addrconf_add_linklocal(idev, &addr);
-	else
-		addrconf_prefix_route(&addr, 64, dev, 0, 0);
+	addrconf_addr_gen(idev, true);
 }
 #endif
 
@@ -4423,6 +4426,10 @@ static int inet6_fill_ifla6_attrs(struct sk_buff *skb, struct inet6_dev *idev)
 	nla = nla_reserve(skb, IFLA_INET6_TOKEN, sizeof(struct in6_addr));
 	if (nla == NULL)
 		goto nla_put_failure;
+
+	if (nla_put_u8(skb, IFLA_INET6_ADDR_GEN_MODE, idev->addr_gen_mode))
+		goto nla_put_failure;
+
 	read_lock_bh(&idev->lock);
 	memcpy(nla_data(nla), idev->token.s6_addr, nla_len(nla));
 	read_unlock_bh(&idev->lock);
@@ -4527,8 +4534,21 @@ static int inet6_set_link_af(struct net_device *dev, const struct nlattr *nla)
 	if (nla_parse_nested(tb, IFLA_INET6_MAX, nla, NULL) < 0)
 		BUG();
 
-	if (tb[IFLA_INET6_TOKEN])
+	if (tb[IFLA_INET6_TOKEN]) {
 		err = inet6_set_iftoken(idev, nla_data(tb[IFLA_INET6_TOKEN]));
+		if (err)
+			return err;
+	}
+
+	if (tb[IFLA_INET6_ADDR_GEN_MODE]) {
+		u8 mode = nla_get_u8(tb[IFLA_INET6_ADDR_GEN_MODE]);
+
+		if (mode != IN6_ADDR_GEN_MODE_EUI64 &&
+		    mode != IN6_ADDR_GEN_MODE_NONE)
+			return -EINVAL;
+		idev->addr_gen_mode = mode;
+		err = 0;
+	}
 
 	return err;
 }