all: allow configuring default-routes as manual, static routes

Up until now, a default-route (with prefix length zero) could not
be configured directly. The user could only set ipv4.gateway,
ipv4.never-default, ipv4.route-metric and ipv4.route-table to influence
the setting of the default-route (respectively for IPv6).

That is a problematic limitation. For one, whether a route has prefix
length zero or non-zero does not make a fundamental difference. Also,
it makes it impossible to configure all the routing attributes that one can
configure otherwise for static routes. For example, the default-route could
not be configured as "onlink", could not have a special MTU, nor could it be
placed in a dedicated routing table.

Fix that by lifting the restriction. Note that "ipv4.never-default" does
not apply to /0 manual routes. Likewise, the previous manners of
configuring default-routes ("ipv4.gateway") don't conflict with manual
default-routes.

Server-side this all the pieces are already in place to accept a default-route
as static routes. This was done by earlier commits like 5c299454b49b
('core: rework tracking of gateway/default-route in ip-config').

A long time ago, NMIPRoute would assert that the prefix length is
positive. That was relaxed by commit a2e93f2de4ac ('libnm: allow zero
prefix length for NMIPRoute'), already before 1.0.0. Using libnm from
before 1.0.0 would result in assertion failures.

Note that the default-route-metric-penalty based on connectivity
checking applies to all /0 routes, even these static routes. Be they
added due to DHCP, "ipv4.gateway", "ipv4.routes" or "wireguard.peer-routes".
I wonder whether doing that unconditionally is desirable, and maybe
there should be a way to opt-out/opt-in for the entire profile or even
per-routes.

https://bugzilla.redhat.com/show_bug.cgi?id=1714438

1 files changed, 20 insertions, 10 deletions

diff --git a/libnm-core/nm-keyfile.c b/libnm-core/nm-keyfile.c
index b0c7a13478..9b032c4cd8 100644
--- a/libnm-core/nm-keyfile.c
+++ b/libnm-core/nm-keyfile.c
@@ -248,15 +248,16 @@ static gpointer
 build_route (KeyfileReaderInfo *info,
              const char *property_name,
              int family,
-             const char *dest_str, guint32 plen,
-             const char *gateway_str, const char *metric_str)
+             const char *dest_str,
+             guint32 plen,
+             const char *gateway_str,
+             const char *metric_str)
 {
 	NMIPRoute *route;
 	guint32 u32;
 	gint64 metric = -1;
 	GError *error = NULL;
 
-	g_return_val_if_fail (plen, NULL);
 	g_return_val_if_fail (dest_str, NULL);
 
 	/* Next hop */
@@ -294,7 +295,10 @@ build_route (KeyfileReaderInfo *info,
 		metric = u32;
 	}
 
-	route = nm_ip_route_new (family, dest_str, plen, gateway_str,
+	route = nm_ip_route_new (family,
+	                         dest_str,
+	                         plen,
+	                         gateway_str,
 	                         metric,
 	                         &error);
 	if (!route) {
@@ -517,8 +521,7 @@ read_one_ip_address_or_route (KeyfileReaderInfo *info,
 
 	/* parse plen, fallback to defaults */
 	if (plen_str) {
-		if (   !get_one_int (info, property_name, plen_str, ipv6 ? 128 : 32, &plen)
-		    || (route && plen == 0)) {
+		if (!get_one_int (info, property_name, plen_str, ipv6 ? 128 : 32, &plen)) {
 			plen = DEFAULT_PREFIX (route, ipv6);
 			if (   info->error
 			    || !handle_warn (info, property_name, NM_KEYFILE_WARN_SEVERITY_WARN,
@@ -536,12 +539,19 @@ read_one_ip_address_or_route (KeyfileReaderInfo *info,
 
 	/* build the appropriate data structure for NetworkManager settings */
 	if (route) {
-		result = build_route (info, property_name,
+		result = build_route (info,
+		                      property_name,
 		                      ipv6 ? AF_INET6 : AF_INET,
-		                      address_str, plen, gateway_str, metric_str);
+		                      address_str,
+		                      plen,
+		                      gateway_str,
+		                      metric_str);
 	} else {
-		result = build_address (info, ipv6 ? AF_INET6 : AF_INET,
-		                        address_str, plen, property_name);
+		result = build_address (info,
+		                        ipv6 ? AF_INET6 : AF_INET,
+		                        address_str,
+		                        plen,
+		                        property_name);
 		if (!result)
 			return NULL;
 		if (gateway_str)