systemd-networkd: Use IFA_F_NOPREFIXROUTE with IPv6 addresses

The IFA_F_NOPREFIXROUTE flag prevents the kernel from creating new onlink
prefixes when a DHCPv6 IPv6 address with a prefix length is set from user
space. IPv6 routing will follow the onlink status from Router Advertisment
Prefix Information options or any manually set route, which is the correct
thing to do.

As this flag has a larger value than what fits into an unsigned char, update
the flag attribute to an uint32_t and set it with an IFA_FLAGS attribute
when writing netlink messages to the kernel.

4 files changed, 25 insertions, 5 deletions

diff --git a/src/network/networkd-address.c b/src/network/networkd-address.c
index 255ff77022..85acc49945 100644
--- a/src/network/networkd-address.c
+++ b/src/network/networkd-address.c
@@ -209,10 +209,18 @@ int address_update(Address *address, Link *link,
         if (r < 0)
                 return log_error_errno(r, "Could not set prefixlen: %m");
 
-        r = sd_rtnl_message_addr_set_flags(req, IFA_F_PERMANENT);
+        address->flags |= IFA_F_PERMANENT;
+
+        r = sd_rtnl_message_addr_set_flags(req, address->flags & 0xff);
         if (r < 0)
                 return log_error_errno(r, "Could not set flags: %m");
 
+        if (address->flags & ~0xff) {
+                r = sd_rtnl_message_append_u32(req, IFA_FLAGS, address->flags);
+                if (r < 0)
+                        return log_error_errno(r, "Could not set extended flags: %m");
+        }
+
         r = sd_rtnl_message_addr_set_scope(req, address->scope);
         if (r < 0)
                 return log_error_errno(r, "Could not set scope: %m");
@@ -335,10 +343,18 @@ int address_configure(Address *address, Link *link,
         if (r < 0)
                 return log_error_errno(r, "Could not set prefixlen: %m");
 
-        r = sd_rtnl_message_addr_set_flags(req, IFA_F_PERMANENT);
+        address->flags |= IFA_F_PERMANENT;
+
+        r = sd_rtnl_message_addr_set_flags(req, (address->flags & 0xff));
         if (r < 0)
                 return log_error_errno(r, "Could not set flags: %m");
 
+        if (address->flags & ~0xff) {
+                r = sd_rtnl_message_append_u32(req, IFA_FLAGS, address->flags);
+                if (r < 0)
+                        return log_error_errno(r, "Could not set extended flags: %m");
+        }
+
         r = sd_rtnl_message_addr_set_scope(req, address->scope);
         if (r < 0)
                 return log_error_errno(r, "Could not set scope: %m");
diff --git a/src/network/networkd-dhcp6.c b/src/network/networkd-dhcp6.c
index bcfad4c03f..283a7d6992 100644
--- a/src/network/networkd-dhcp6.c
+++ b/src/network/networkd-dhcp6.c
@@ -65,7 +65,9 @@ static int dhcp6_address_update(Link *link, struct in6_addr *ip6_addr,
 
         addr->family = AF_INET6;
         memcpy(&addr->in_addr.in6, ip6_addr, sizeof(*ip6_addr));
-        addr->prefixlen = prefixlen;
+
+        addr->flags = IFA_F_NOPREFIXROUTE;
+        addr->prefixlen = 64;
 
         addr->cinfo.ifa_prefered = lifetime_preferred;
         addr->cinfo.ifa_valid = lifetime_valid;
diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 842ca1ce6e..437c59843e 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -1831,6 +1831,7 @@ int link_rtnl_process_address(sd_rtnl *rtnl, sd_rtnl_message *message, void *use
         Link *link = NULL;
         uint16_t type;
         _cleanup_address_free_ Address *address = NULL;
+        unsigned char flags;
         Address *existing;
         char buf[INET6_ADDRSTRLEN], valid_buf[FORMAT_TIMESPAN_MAX];
         const char *valid_str = NULL;
@@ -1894,11 +1895,12 @@ int link_rtnl_process_address(sd_rtnl *rtnl, sd_rtnl_message *message, void *use
                 return 0;
         }
 
-        r = sd_rtnl_message_addr_get_flags(message, &address->flags);
+        r = sd_rtnl_message_addr_get_flags(message, &flags);
         if (r < 0) {
                 log_link_warning(link, "rtnl: received address with invalid flags, ignoring");
                 return 0;
         }
+        address->flags = flags;
 
         switch (address->family) {
         case AF_INET:
diff --git a/src/network/networkd.h b/src/network/networkd.h
index 8bdc2bed82..c26d64e383 100644
--- a/src/network/networkd.h
+++ b/src/network/networkd.h
@@ -173,7 +173,7 @@ struct Address {
         int family;
         unsigned char prefixlen;
         unsigned char scope;
-        unsigned char flags;
+        uint32_t flags;
         char *label;
 
         struct in_addr broadcast;