net: Add new protocol attribute to IP addresses

This patch adds a new protocol attribute to IPv4 and IPv6 addresses.
Inspiration was taken from the protocol attribute of routes. User space
applications like iproute2 can set/get the protocol with the Netlink API.

The attribute is stored as an 8-bit unsigned integer.

The protocol attribute is set by kernel for these categories:

- IPv4 and IPv6 loopback addresses
- IPv6 addresses generated from router announcements
- IPv6 link local addresses

User space may pass custom protocols, not defined by the kernel.

Grouping addresses on their origin is useful in scenarios where you want
to distinguish between addresses based on who added them, e.g. kernel
vs. user space.

Tagging addresses with a string label is an existing feature that could be
used as a solution. Unfortunately the max length of a label is
15 characters, and for compatibility reasons the label must be prefixed
with the name of the device followed by a colon. Since device names also
have a max length of 15 characters, only -1 characters is guaranteed to be
available for any origin tag, which is not that much.

A reference implementation of user space setting and getting protocols
is available for iproute2:

https://github.com/westermo/iproute2/commit/9a6ea18bd79f47f293e5edc7780f315ea42ff540

Signed-off-by: Jacques de Laval <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/linux/inetdevice.h

···
 	__be32			ifa_broadcast;
 	unsigned char		ifa_scope;
 	unsigned char		ifa_prefixlen;
+	unsigned char		ifa_proto;
 	__u32			ifa_flags;
 	char			ifa_label[IFNAMSIZ];
 

include/net/addrconf.h

···
 	const struct in6_addr	*pfx;
 	unsigned int		plen;
 
+	u8			ifa_proto;
+
 	const struct in6_addr	*peer_pfx;
 
 	u32			rt_priority;

include/net/if_inet6.h

···
 
 	bool			tokenized;
 
+	u8			ifa_proto;
+
 	struct rcu_head		rcu;
 	struct in6_addr		peer_addr;
 };

include/uapi/linux/if_addr.h

···
 	IFA_CACHEINFO,
 	IFA_MULTICAST,
 	IFA_FLAGS,
-	IFA_RT_PRIORITY,  /* u32, priority/metric for prefix route */
+	IFA_RT_PRIORITY,	/* u32, priority/metric for prefix route */
 	IFA_TARGET_NETNSID,
+	IFA_PROTO,		/* u8, address protocol */
 	__IFA_MAX,
 };
 
···
 #define IFA_RTA(r)  ((struct rtattr*)(((char*)(r)) + NLMSG_ALIGN(sizeof(struct ifaddrmsg))))
 #define IFA_PAYLOAD(n) NLMSG_PAYLOAD(n,sizeof(struct ifaddrmsg))
 #endif
+
+/* ifa_proto */
+#define IFAPROT_UNSPEC		0
+#define IFAPROT_KERNEL_LO	1	/* loopback */
+#define IFAPROT_KERNEL_RA	2	/* set by kernel from router announcement */
+#define IFAPROT_KERNEL_LL	3	/* link-local set by kernel */
 
 #endif

net/ipv4/devinet.c

···
 	[IFA_FLAGS]		= { .type = NLA_U32 },
 	[IFA_RT_PRIORITY]	= { .type = NLA_U32 },
 	[IFA_TARGET_NETNSID]	= { .type = NLA_S32 },
+	[IFA_PROTO]		= { .type = NLA_U8 },
 };
 
 struct inet_fill_args {
···
 	if (tb[IFA_RT_PRIORITY])
 		ifa->ifa_rt_priority = nla_get_u32(tb[IFA_RT_PRIORITY]);
 
+	if (tb[IFA_PROTO])
+		ifa->ifa_proto = nla_get_u8(tb[IFA_PROTO]);
+
 	if (tb[IFA_CACHEINFO]) {
 		struct ifa_cacheinfo *ci;
 
···
 	       + nla_total_size(4) /* IFA_BROADCAST */
 	       + nla_total_size(IFNAMSIZ) /* IFA_LABEL */
 	       + nla_total_size(4)  /* IFA_FLAGS */
+	       + nla_total_size(1)  /* IFA_PROTO */
 	       + nla_total_size(4)  /* IFA_RT_PRIORITY */
 	       + nla_total_size(sizeof(struct ifa_cacheinfo)); /* IFA_CACHEINFO */
 }
···
 	     nla_put_in_addr(skb, IFA_BROADCAST, ifa->ifa_broadcast)) ||
 	    (ifa->ifa_label[0] &&
 	     nla_put_string(skb, IFA_LABEL, ifa->ifa_label)) ||
+	    (ifa->ifa_proto &&
+	     nla_put_u8(skb, IFA_PROTO, ifa->ifa_proto)) ||
 	    nla_put_u32(skb, IFA_FLAGS, ifa->ifa_flags) ||
 	    (ifa->ifa_rt_priority &&
 	     nla_put_u32(skb, IFA_RT_PRIORITY, ifa->ifa_rt_priority)) ||

net/ipv6/addrconf.c

···
 	ifa->prefix_len = cfg->plen;
 	ifa->rt_priority = cfg->rt_priority;
 	ifa->flags = cfg->ifa_flags;
+	ifa->ifa_proto = cfg->ifa_proto;
 	/* No need to add the TENTATIVE flag for addresses with NODAD */
 	if (!(cfg->ifa_flags & IFA_F_NODAD))
 		ifa->flags |= IFA_F_TENTATIVE;
···
 			.valid_lft = valid_lft,
 			.preferred_lft = prefered_lft,
 			.scope = addr_type & IPV6_ADDR_SCOPE_MASK,
+			.ifa_proto = IFAPROT_KERNEL_RA
 		};
 
 #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
···
 }
 
 static void add_addr(struct inet6_dev *idev, const struct in6_addr *addr,
-		     int plen, int scope)
+		     int plen, int scope, u8 proto)
 {
 	struct inet6_ifaddr *ifp;
 	struct ifa6_config cfg = {
···
 		.ifa_flags = IFA_F_PERMANENT,
 		.valid_lft = INFINITY_LIFE_TIME,
 		.preferred_lft = INFINITY_LIFE_TIME,
-		.scope = scope
+		.scope = scope,
+		.ifa_proto = proto
 	};
 
 	ifp = ipv6_add_addr(idev, &cfg, true, NULL);
···
 	}
 
 	if (addr.s6_addr32[3]) {
-		add_addr(idev, &addr, plen, scope);
+		add_addr(idev, &addr, plen, scope, IFAPROT_UNSPEC);
 		addrconf_prefix_route(&addr, plen, 0, idev->dev, 0, pflags,
 				      GFP_KERNEL);
 		return;
···
 					flag |= IFA_HOST;
 				}
 
-				add_addr(idev, &addr, plen, flag);
+				add_addr(idev, &addr, plen, flag,
+					 IFAPROT_UNSPEC);
 				addrconf_prefix_route(&addr, plen, 0, idev->dev,
 						      0, pflags, GFP_KERNEL);
 			}
···
 		return;
 	}
 
-	add_addr(idev, &in6addr_loopback, 128, IFA_HOST);
+	add_addr(idev, &in6addr_loopback, 128, IFA_HOST, IFAPROT_KERNEL_LO);
 }
 
 void addrconf_add_linklocal(struct inet6_dev *idev,
···
 		.ifa_flags = flags | IFA_F_PERMANENT,
 		.valid_lft = INFINITY_LIFE_TIME,
 		.preferred_lft = INFINITY_LIFE_TIME,
-		.scope = IFA_LINK
+		.scope = IFA_LINK,
+		.ifa_proto = IFAPROT_KERNEL_LL
 	};
 	struct inet6_ifaddr *ifp;
 
···
 	[IFA_FLAGS]		= { .len = sizeof(u32) },
 	[IFA_RT_PRIORITY]	= { .len = sizeof(u32) },
 	[IFA_TARGET_NETNSID]	= { .type = NLA_S32 },
+	[IFA_PROTO]		= { .type = NLA_U8 },
 };
 
 static int
···
 	ifp->tstamp = jiffies;
 	ifp->valid_lft = cfg->valid_lft;
 	ifp->prefered_lft = cfg->preferred_lft;
+	ifp->ifa_proto = cfg->ifa_proto;
 
 	if (cfg->rt_priority && cfg->rt_priority != ifp->rt_priority)
 		ifp->rt_priority = cfg->rt_priority;
···
 	cfg.plen = ifm->ifa_prefixlen;
 	if (tb[IFA_RT_PRIORITY])
 		cfg.rt_priority = nla_get_u32(tb[IFA_RT_PRIORITY]);
+
+	if (tb[IFA_PROTO])
+		cfg.ifa_proto = nla_get_u8(tb[IFA_PROTO]);
 
 	cfg.valid_lft = INFINITY_LIFE_TIME;
 	cfg.preferred_lft = INFINITY_LIFE_TIME;
···
 	       + nla_total_size(16) /* IFA_ADDRESS */
 	       + nla_total_size(sizeof(struct ifa_cacheinfo))
 	       + nla_total_size(4)  /* IFA_FLAGS */
+	       + nla_total_size(1)  /* IFA_PROTO */
 	       + nla_total_size(4)  /* IFA_RT_PRIORITY */;
 }
 
···
 		goto error;
 
 	if (nla_put_u32(skb, IFA_FLAGS, ifa->flags) < 0)
+		goto error;
+
+	if (ifa->ifa_proto &&
+	    nla_put_u8(skb, IFA_PROTO, ifa->ifa_proto))
 		goto error;
 
 	nlmsg_end(skb, nlh);