From 95002535b32ca05b4fa03a49afa211c4271bea1d Mon Sep 17 00:00:00 2001
From: Jo-Philipp Wich <jo@mein.io>
Date: Wed, 16 Feb 2022 17:58:42 +0100
Subject: [PATCH] getifaddr.c: prefer non-reserved over reserved addresses in
 `getifaddr()`

When iterating interface addresses obtained via `getifaddrs()`, don't
stop at the first found IPv4 address but continue checking all IPv4
addresses and prefer to use a non-reserved one in case an interface
has both reserved (private) and non-reserved (public) addresses
assigned.

After this fix, miniupnpd on OpenWrt is able to properly detect the
external IP address of an external interface with both a private
RFC1918 and a public IP assigned regardless of whether `getifaddrs()`
happens to return the private or the public IPv4 address first.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
---
 miniupnpd/getifaddr.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/miniupnpd/getifaddr.c b/miniupnpd/getifaddr.c
index 7c09064..67ec235 100644
--- a/miniupnpd/getifaddr.c
+++ b/miniupnpd/getifaddr.c
@@ -101,6 +101,7 @@ getifaddr(const char * ifname, char * buf, int len,
 	/* Works for all address families (both ip v4 and ip v6) */
 	struct ifaddrs * ifap;
 	struct ifaddrs * ife;
+	struct ifaddrs * candidate = NULL;
 
 	if(!ifname || ifname[0]=='\0')
 		return -1;
@@ -119,14 +120,10 @@ getifaddr(const char * ifname, char * buf, int len,
 		switch(ife->ifa_addr->sa_family)
 		{
 		case AF_INET:
-			if(buf)
-			{
-				inet_ntop(ife->ifa_addr->sa_family,
-				          &((struct sockaddr_in *)ife->ifa_addr)->sin_addr,
-				          buf, len);
-			}
-			if(addr) *addr = ((struct sockaddr_in *)ife->ifa_addr)->sin_addr;
-			if(mask) *mask = ((struct sockaddr_in *)ife->ifa_netmask)->sin_addr;
+			if(!candidate ||
+			   (addr_is_reserved(&((struct sockaddr_in *)candidate->ifa_addr)->sin_addr) &&
+			    !addr_is_reserved(&((struct sockaddr_in *)ife->ifa_addr)->sin_addr)))
+				candidate = ife;
 			break;
 /*
 		case AF_INET6:
@@ -136,6 +133,17 @@ getifaddr(const char * ifname, char * buf, int len,
 */
 		}
 	}
+	if(candidate)
+	{
+		if(buf)
+		{
+			inet_ntop(candidate->ifa_addr->sa_family,
+			          &((struct sockaddr_in *)candidate->ifa_addr)->sin_addr,
+			          buf, len);
+		}
+		if(addr) *addr = ((struct sockaddr_in *)candidate->ifa_addr)->sin_addr;
+		if(mask) *mask = ((struct sockaddr_in *)candidate->ifa_netmask)->sin_addr;
+	}
 	freeifaddrs(ifap);
 #endif
 	return 0;