[PATCH ovpn net 4/5] ovpn: reject invalid peer VPN addresses

In MP mode, ovpn uses peer VPN addresses as lookup keys for selecting
the peer that should receive outgoing tunnel packets. The netlink
configuration path currently accepts address values that cannot sensibly
identify a VPN peer, such as multicast, broadcast or loopback addresses.

Reject invalid peer VPN addresses when creating or updating an MP peer.
Keep accepting the unspecified address as the internal unset value,
provided that at least one VPN address family remains configured.

Fixes: 1d36a36f6d53 ("ovpn: implement peer add/get/dump/delete via netlink")
Signed-off-by: Ralf Lici <[email protected]>
---
 drivers/net/ovpn/netlink.c | 50 ++++++++++++++++++++++++++++++--------
 1 file changed, 40 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ovpn/netlink.c b/drivers/net/ovpn/netlink.c
index 43e6c7a29a6f..333e9237e594 100644
--- a/drivers/net/ovpn/netlink.c
+++ b/drivers/net/ovpn/netlink.c
@@ -179,6 +179,39 @@ static sa_family_t ovpn_nl_family_get(struct nlattr *addr4,
 	return AF_UNSPEC;
 }
 
+static int ovpn_nl_peer_check_vpn_addrs(const struct in_addr *addr4,
+					const struct in6_addr *addr6,
+					struct genl_info *info)
+{
+	int addr6_type;
+
+	if (addr4->s_addr == htonl(INADDR_ANY) && ipv6_addr_any(addr6)) {
+		NL_SET_ERR_MSG_MOD(info->extack,
+				   "at least one VPN IP must be configured");
+		return -EINVAL;
+	}
+
+	if (ipv4_is_multicast(addr4->s_addr) || ipv4_is_lbcast(addr4->s_addr) ||
+	    ipv4_is_loopback(addr4->s_addr)) {
+		NL_SET_ERR_MSG_MOD(info->extack,
+				   "VPN IPv4 address must be valid unicast or any");
+		return -EADDRNOTAVAIL;
+	}
+
+	if (!ipv6_addr_any(addr6)) {
+		addr6_type = ipv6_addr_type(addr6);
+
+		if (!(addr6_type & IPV6_ADDR_UNICAST) ||
+		    (addr6_type & (IPV6_ADDR_LOOPBACK | IPV6_ADDR_COMPATv4))) {
+			NL_SET_ERR_MSG_MOD(info->extack,
+					   "VPN IPv6 address must be valid unicast or any");
+			return -EADDRNOTAVAIL;
+		}
+	}
+
+	return 0;
+}
+
 static int ovpn_nl_peer_precheck(struct ovpn_priv *ovpn,
 				 struct genl_info *info,
 				 struct nlattr **attrs)
@@ -381,11 +414,10 @@ int ovpn_nl_peer_new_doit(struct sk_buff *skb, struct genl_info *info)
 			vpn_addr6 =
 				nla_get_in6_addr(attrs[OVPN_A_PEER_VPN_IPV6]);
 
-		if (!vpn_addr4.s_addr && ipv6_addr_any(&vpn_addr6)) {
-			NL_SET_ERR_MSG_FMT_MOD(info->extack,
-					       "VPN IP must be provided in MP mode");
-			return -EINVAL;
-		}
+		ret = ovpn_nl_peer_check_vpn_addrs(&vpn_addr4, &vpn_addr6,
+						   info);
+		if (ret < 0)
+			return ret;
 	}
 
 	peer_id = nla_get_u32(attrs[OVPN_A_PEER_ID]);
@@ -547,12 +579,10 @@ int ovpn_nl_peer_set_doit(struct sk_buff *skb, struct genl_info *info)
 	/* in MP mode VPN IPs are required for selecting the right peer */
 	if (ovpn->mode == OVPN_MODE_MP &&
 	    (attrs[OVPN_A_PEER_VPN_IPV4] || attrs[OVPN_A_PEER_VPN_IPV6])) {
-		if (!vpn_addr4.s_addr && ipv6_addr_any(&vpn_addr6)) {
-			NL_SET_ERR_MSG_FMT_MOD(info->extack,
-					       "MP peer must have at least one valid VPN IP");
-			ret = -EINVAL;
+		ret = ovpn_nl_peer_check_vpn_addrs(&vpn_addr4, &vpn_addr6,
+						   info);
+		if (ret < 0)
 			goto unlock;
-		}
 
 		/* reject peer with conflicting VPN address */
 		if (ovpn_peer_vpn_addr_conflict(ovpn, peer, &vpn_addr4,
-- 
2.55.0