vxlan: check valid combinations of address scopes

* Multicast addresses are never valid as local address
* Link-local IPv6 unicast addresses may only be used as remote when the
  local address is link-local as well
* Don't allow link-local IPv6 local/remote addresses without interface

We also store in the flags field if link-local addresses are used for the
follow-up patches that actually make VXLAN over link-local IPv6 work.
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -2907,11 +2907,35 @@ static int vxlan_config_validate(struct net *src_net, struct vxlan_config *conf,
 	if (conf->saddr.sa.sa_family != conf->remote_ip.sa.sa_family)
 		return -EINVAL;
 
+	if (vxlan_addr_multicast(&conf->saddr))
+		return -EINVAL;
+
 	if (conf->saddr.sa.sa_family == AF_INET6) {
 		if (!IS_ENABLED(CONFIG_IPV6))
 			return -EPFNOSUPPORT;
 		use_ipv6 = true;
 		conf->flags |= VXLAN_F_IPV6;
+
+		if (!(conf->flags & VXLAN_F_COLLECT_METADATA)) {
+			int local_type =
+				ipv6_addr_type(&conf->saddr.sin6.sin6_addr);
+			int remote_type =
+				ipv6_addr_type(&conf->remote_ip.sin6.sin6_addr);
+
+			if (local_type & IPV6_ADDR_LINKLOCAL) {
+				if (!(remote_type & IPV6_ADDR_LINKLOCAL) &&
+				    (remote_type != IPV6_ADDR_ANY))
+					return -EINVAL;
+
+				conf->flags |= VXLAN_F_IPV6_LINKLOCAL;
+			} else {
+				if (remote_type ==
+				    (IPV6_ADDR_UNICAST | IPV6_ADDR_LINKLOCAL))
+					return -EINVAL;
+
+				conf->flags &= ~VXLAN_F_IPV6_LINKLOCAL;
+			}
+		}
 	}
 
 	if (conf->label && !use_ipv6)
@@ -2937,6 +2961,11 @@ static int vxlan_config_validate(struct net *src_net, struct vxlan_config *conf,
 		if (vxlan_addr_multicast(&conf->remote_ip))
 			return -EINVAL;
 
+#if IS_ENABLED(CONFIG_IPV6)
+		if (conf->flags & VXLAN_F_IPV6_LINKLOCAL)
+			return -EINVAL;
+#endif
+
 		*lower = NULL;
 	}
 

include/net/vxlan.h

@@ -258,6 +258,7 @@ struct vxlan_dev {
 #define VXLAN_F_REMCSUM_NOPARTIAL	0x1000
 #define VXLAN_F_COLLECT_METADATA	0x2000
 #define VXLAN_F_GPE			0x4000
+#define VXLAN_F_IPV6_LINKLOCAL		0x8000
 
 /* Flags that are used in the receive path. These flags must match in
  * order for a socket to be shareable
@@ -272,6 +273,7 @@ struct vxlan_dev {
 /* Flags that can be set together with VXLAN_F_GPE. */
 #define VXLAN_F_ALLOWED_GPE		(VXLAN_F_GPE |			\
 					 VXLAN_F_IPV6 |			\
+					 VXLAN_F_IPV6_LINKLOCAL |	\
 					 VXLAN_F_UDP_ZERO_CSUM_TX |	\
 					 VXLAN_F_UDP_ZERO_CSUM6_TX |	\
 					 VXLAN_F_UDP_ZERO_CSUM6_RX |	\