net: ipv6: Select proper IPv6 source address for privacy extension

If IPv6 privacy extension is enabled, then we need to select
proper public or temporary IPv6 source address when sending the
packet.

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

include/net/net_if.h

@@ -1114,7 +1114,7 @@ static inline void net_if_ipv6_maddr_leave(struct net_if_mcast_addr *addr)
  * @return Pointer to prefix, NULL if not found.
  */
 struct net_if_ipv6_prefix *net_if_ipv6_prefix_get(struct net_if *iface,
-						  struct in6_addr *addr);
+						  const struct in6_addr *addr);
 
 /**
  * @brief Check if this IPv6 prefix belongs to this interface

subsys/net/ip/net_if.c

@@ -2006,7 +2006,7 @@ bool net_if_ipv6_prefix_rm(struct net_if *iface, struct in6_addr *addr,
 }
 
 struct net_if_ipv6_prefix *net_if_ipv6_prefix_get(struct net_if *iface,
-						  struct in6_addr *addr)
+						  const struct in6_addr *addr)
 {
 	struct net_if_ipv6_prefix *prefix = NULL;
 	struct net_if_ipv6 *ipv6;
@@ -2269,25 +2269,53 @@ static inline bool is_proper_ipv6_address(struct net_if_addr *addr)
 	return false;
 }
 
+static bool use_public_address(bool prefer_public, bool is_temporary)
+{
+	if (IS_ENABLED(CONFIG_NET_IPV6_PE_ENABLE)) {
+		if (!prefer_public && is_temporary) {
+			return false;
+		}
+	}
+
+	return true;
+}
+
 static struct in6_addr *net_if_ipv6_get_best_match(struct net_if *iface,
 						   const struct in6_addr *dst,
+						   u8_t prefix_len,
 						   u8_t *best_so_far)
 {
 	struct net_if_ipv6 *ipv6 = iface->config.ip.ipv6;
+	struct net_if_addr *public_addr = NULL;
 	struct in6_addr *src = NULL;
-	u8_t len;
+	u8_t public_addr_len = 0;
+	struct in6_addr *temp_addr;
+	u8_t len, temp_addr_len;
+	bool ret;
 	int i;
 
 	if (!ipv6) {
 		return NULL;
 	}
 
+	if (IS_ENABLED(CONFIG_NET_IPV6_PE_ENABLE)) {
+		temp_addr = NULL;
+		temp_addr_len = 0;
+	} else {
+		ARG_UNUSED(temp_addr);
+		ARG_UNUSED(temp_addr_len);
+	}
+
 	for (i = 0; i < NET_IF_MAX_IPV6_ADDR; i++) {
 		if (!is_proper_ipv6_address(&ipv6->unicast[i])) {
 			continue;
 		}
 
 		len = get_diff_ipv6(dst, &ipv6->unicast[i].address.in6_addr);
+		if (len >= prefix_len) {
+			len = prefix_len;
+		}
+
 		if (len >= *best_so_far) {
 			/* Mesh local address can only be selected for the same
 			 * subnet.
@@ -2296,11 +2324,39 @@ static struct in6_addr *net_if_ipv6_get_best_match(struct net_if *iface,
 				continue;
 			}
 
+			ret = use_public_address(iface->pe_prefer_public,
+						 ipv6->unicast[i].is_temporary);
+			if (!ret) {
+				temp_addr = &ipv6->unicast[i].address.in6_addr;
+				temp_addr_len = len;
+				continue;
+			}
+
+			if (!ipv6->unicast[i].is_temporary) {
+				public_addr = &ipv6->unicast[i];
+				public_addr_len = len;
+			}
+
 			*best_so_far = len;
 			src = &ipv6->unicast[i].address.in6_addr;
 		}
 	}
 
+	if (IS_ENABLED(CONFIG_NET_IPV6_PE_ENABLE) &&
+	    !iface->pe_prefer_public && temp_addr) {
+		if (temp_addr_len >= *best_so_far) {
+			*best_so_far = temp_addr_len;
+			src = temp_addr;
+		}
+	} else {
+		/* By default prefer always public address if found */
+		if (public_addr &&
+		    !net_ipv6_addr_cmp(&public_addr->address.in6_addr, src)) {
+			src = &public_addr->address.in6_addr;
+			*best_so_far = public_addr_len;
+		}
+	}
+
 	return src;
 }
 
@@ -2312,13 +2368,21 @@ const struct in6_addr *net_if_ipv6_select_src_addr(struct net_if *dst_iface,
 	struct net_if *iface;
 
 	if (!net_ipv6_is_ll_addr(dst) && !net_ipv6_is_addr_mcast(dst)) {
+		struct net_if_ipv6_prefix *prefix;
+		u8_t prefix_len = 128;
+
+		prefix = net_if_ipv6_prefix_get(dst_iface, dst);
+		if (prefix) {
+			prefix_len = prefix->len;
+		}
 
 		for (iface = __net_if_start;
 		     !dst_iface && iface != __net_if_end;
 		     iface++) {
 			struct in6_addr *addr;
 
 			addr = net_if_ipv6_get_best_match(iface, dst,
+							  prefix_len,
 							  &best_match);
 			if (addr) {
 				src = addr;
@@ -2328,6 +2392,7 @@ const struct in6_addr *net_if_ipv6_select_src_addr(struct net_if *dst_iface,
 		/* If caller has supplied interface, then use that */
 		if (dst_iface) {
 			src = net_if_ipv6_get_best_match(dst_iface, dst,
+							 prefix_len,
 							 &best_match);
 		}