network: attempt to trigger kernel IPv6LL address generation

Try to ensure kernel IPv6 link local address generation occurs by
setting the per-if addr_gen_mode sysctl when the link is already up,
instead of the netlink interface (IFLA_INET6_ADDR_GEN_MODE).

The netlink setting is sufficient in cases where the interface is not
yet up when networkd configures an interface - bringing the interface
up will trigger in-kernel address generation.

If the interface is already up, yet the interface has no IPv6LL assigned
setting IFLA_INET6_ADDR_GEN_MODE has no effect.

Writing the addr_gen_mode sysctl is a best effort attempt at triggering
address generation regardless of interface state because it also works
in cases where the interface is already up.

Fixes #22424.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/network/networkd-ipv6ll.c b/src/network/networkd-ipv6ll.c
index 992be2fca6..79cf679daf 100644
--- a/src/network/networkd-ipv6ll.c
+++ b/src/network/networkd-ipv6ll.c
@@ -223,6 +223,16 @@ int link_set_ipv6ll_stable_secret(Link *link) {
         return sysctl_write_ip_property(AF_INET6, link->ifname, "stable_secret", str);
 }
 
+int link_set_ipv6ll_addrgen_mode(Link *link, IPv6LinkLocalAddressGenMode mode) {
+        assert(link);
+        assert(mode >= 0 && mode < _IPV6_LINK_LOCAL_ADDRESS_GEN_MODE_MAX);
+
+        if (mode == link->ipv6ll_address_gen_mode)
+                return 0;
+
+        return sysctl_write_ip_property_uint32(AF_INET6, link->ifname, "addr_gen_mode", mode);
+}
+
 static const char* const ipv6_link_local_address_gen_mode_table[_IPV6_LINK_LOCAL_ADDRESS_GEN_MODE_MAX] = {
         [IPV6_LINK_LOCAL_ADDRESSS_GEN_MODE_EUI64]          = "eui64",
         [IPV6_LINK_LOCAL_ADDRESSS_GEN_MODE_NONE]           = "none",