fou: Support binding FoU socket

An FoU socket is currently bound to the wildcard-address. While this
works fine, there are several use-cases where the use of the
wildcard-address is not desirable. For example, I use FoU on some
multi-homed servers and would like to use FoU on only one of the
interfaces.

This commit adds support for binding FoU sockets to a given source
address/interface, as well as connecting the socket to a given
destination address/port. udp_tunnel already provides the required
infrastructure, so most of the code added is for exposing and setting
the different attributes (local address, peer address, etc.).

The lookups performed when we add, delete or get an FoU-socket has also
been updated to compare all the attributes a user can set. Since the
comparison now involves several elements, I have added a separate
comparison-function instead of open-coding.

In order to test the code and ensure that the new comparison code works
correctly, I started by creating a wildcard socket bound to port 1234 on
my machine. I then tried to create a non-wildcarded socket bound to the
same port, as well as fetching and deleting the socket (including source
address, peer address or interface index in the netlink request).  Both
the create, fetch and delete request failed. Deleting/fetching the
socket was only successful when my netlink request attributes matched
those used to create the socket.

I then repeated the tests, but with a socket bound to a local ip
address, a socket bound to a local address + interface, and a bound
socket that was also «connected» to a peer. Add only worked when no
socket with the matching source address/interface (or wildcard) existed,
while fetch/delete was only successful when all attributes matched.

In addition to testing that the new code work, I also checked that the
current behavior is kept. If none of the new attributes are provided,
then an FoU-socket is configured as before (i.e., wildcarded).  If any
of the new attributes are provided, the FoU-socket is configured as
expected.

v1->v2:
* Fixed building with IPv6 disabled (kbuild).
* Fixed a return type warning and make the ugly comparison function more
readable (kbuild).
* Describe more in detail what has been tested (thanks David Miller).
* Make peer port required if peer address is specified.

Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/fou.h

@@ -16,6 +16,12 @@ enum {
 	FOU_ATTR_IPPROTO,			/* u8 */
 	FOU_ATTR_TYPE,				/* u8 */
 	FOU_ATTR_REMCSUM_NOPARTIAL,		/* flag */
+	FOU_ATTR_LOCAL_V4,			/* u32 */
+	FOU_ATTR_LOCAL_V6,			/* in6_addr */
+	FOU_ATTR_PEER_V4,			/* u32 */
+	FOU_ATTR_PEER_V6,			/* in6_addr */
+	FOU_ATTR_PEER_PORT,			/* u16 */
+	FOU_ATTR_IFINDEX,			/* s32 */
 
 	__FOU_ATTR_MAX,
 };

net/ipv4/fou.c

@@ -499,15 +499,45 @@ out_unlock:
 	return err;
 }
 
-static int fou_add_to_port_list(struct net *net, struct fou *fou)
+static bool fou_cfg_cmp(struct fou *fou, struct fou_cfg *cfg)
+{
+	struct sock *sk = fou->sock->sk;
+	struct udp_port_cfg *udp_cfg = &cfg->udp_config;
+
+	if (fou->family != udp_cfg->family ||
+	    fou->port != udp_cfg->local_udp_port ||
+	    sk->sk_dport != udp_cfg->peer_udp_port ||
+	    sk->sk_bound_dev_if != udp_cfg->bind_ifindex)
+		return false;
+
+	if (fou->family == AF_INET) {
+		if (sk->sk_rcv_saddr != udp_cfg->local_ip.s_addr ||
+		    sk->sk_daddr != udp_cfg->peer_ip.s_addr)
+			return false;
+		else
+			return true;
+#if IS_ENABLED(CONFIG_IPV6)
+	} else {
+		if (ipv6_addr_cmp(&sk->sk_v6_rcv_saddr, &udp_cfg->local_ip6) ||
+		    ipv6_addr_cmp(&sk->sk_v6_daddr, &udp_cfg->peer_ip6))
+			return false;
+		else
+			return true;
+#endif
+	}
+
+	return false;
+}
+
+static int fou_add_to_port_list(struct net *net, struct fou *fou,
+				struct fou_cfg *cfg)
 {
 	struct fou_net *fn = net_generic(net, fou_net_id);
 	struct fou *fout;
 
 	mutex_lock(&fn->fou_lock);
 	list_for_each_entry(fout, &fn->fou_list, list) {
-		if (fou->port == fout->port &&
+		if (fou_cfg_cmp(fout, cfg)) {
-		    fou->family == fout->family) {
 			mutex_unlock(&fn->fou_lock);
 			return -EALREADY;
 		}
@@ -585,7 +615,7 @@ static int fou_create(struct net *net, struct fou_cfg *cfg,
 
 	sk->sk_allocation = GFP_ATOMIC;
 
-	err = fou_add_to_port_list(net, fou);
+	err = fou_add_to_port_list(net, fou, cfg);
 	if (err)
 		goto error;
 
@@ -605,14 +635,12 @@ error:
 static int fou_destroy(struct net *net, struct fou_cfg *cfg)
 {
 	struct fou_net *fn = net_generic(net, fou_net_id);
-	__be16 port = cfg->udp_config.local_udp_port;
-	u8 family = cfg->udp_config.family;
 	int err = -EINVAL;
 	struct fou *fou;
 
 	mutex_lock(&fn->fou_lock);
 	list_for_each_entry(fou, &fn->fou_list, list) {
-		if (fou->port == port && fou->family == family) {
+		if (fou_cfg_cmp(fou, cfg)) {
 			fou_release(fou);
 			err = 0;
 			break;
@@ -626,16 +654,27 @@ static int fou_destroy(struct net *net, struct fou_cfg *cfg)
 static struct genl_family fou_nl_family;
 
 static const struct nla_policy fou_nl_policy[FOU_ATTR_MAX + 1] = {
-	[FOU_ATTR_PORT] = { .type = NLA_U16, },
+	[FOU_ATTR_PORT]			= { .type = NLA_U16, },
-	[FOU_ATTR_AF] = { .type = NLA_U8, },
+	[FOU_ATTR_AF]			= { .type = NLA_U8, },
-	[FOU_ATTR_IPPROTO] = { .type = NLA_U8, },
+	[FOU_ATTR_IPPROTO]		= { .type = NLA_U8, },
-	[FOU_ATTR_TYPE] = { .type = NLA_U8, },
+	[FOU_ATTR_TYPE]			= { .type = NLA_U8, },
-	[FOU_ATTR_REMCSUM_NOPARTIAL] = { .type = NLA_FLAG, },
+	[FOU_ATTR_REMCSUM_NOPARTIAL]	= { .type = NLA_FLAG, },
+	[FOU_ATTR_LOCAL_V4]		= { .type = NLA_U32, },
+	[FOU_ATTR_PEER_V4]		= { .type = NLA_U32, },
+	[FOU_ATTR_LOCAL_V6]		= { .type = sizeof(struct in6_addr), },
+	[FOU_ATTR_PEER_V6]		= { .type = sizeof(struct in6_addr), },
+	[FOU_ATTR_PEER_PORT]		= { .type = NLA_U16, },
+	[FOU_ATTR_IFINDEX]		= { .type = NLA_S32, },
 };
 
 static int parse_nl_config(struct genl_info *info,
 			   struct fou_cfg *cfg)
 {
+	bool has_local = false, has_peer = false;
+	struct nlattr *attr;
+	int ifindex;
+	__be16 port;
+
 	memset(cfg, 0, sizeof(*cfg));
 
 	cfg->udp_config.family = AF_INET;
@@ -657,8 +696,7 @@ static int parse_nl_config(struct genl_info *info,
 	}
 
 	if (info->attrs[FOU_ATTR_PORT]) {
-		__be16 port = nla_get_be16(info->attrs[FOU_ATTR_PORT]);
+		port = nla_get_be16(info->attrs[FOU_ATTR_PORT]);
-
 		cfg->udp_config.local_udp_port = port;
 	}
 
@@ -671,6 +709,52 @@ static int parse_nl_config(struct genl_info *info,
 	if (info->attrs[FOU_ATTR_REMCSUM_NOPARTIAL])
 		cfg->flags |= FOU_F_REMCSUM_NOPARTIAL;
 
+	if (cfg->udp_config.family == AF_INET) {
+		if (info->attrs[FOU_ATTR_LOCAL_V4]) {
+			attr = info->attrs[FOU_ATTR_LOCAL_V4];
+			cfg->udp_config.local_ip.s_addr = nla_get_in_addr(attr);
+			has_local = true;
+		}
+
+		if (info->attrs[FOU_ATTR_PEER_V4]) {
+			attr = info->attrs[FOU_ATTR_PEER_V4];
+			cfg->udp_config.peer_ip.s_addr = nla_get_in_addr(attr);
+			has_peer = true;
+		}
+#if IS_ENABLED(CONFIG_IPV6)
+	} else {
+		if (info->attrs[FOU_ATTR_LOCAL_V6]) {
+			attr = info->attrs[FOU_ATTR_LOCAL_V6];
+			cfg->udp_config.local_ip6 = nla_get_in6_addr(attr);
+			has_local = true;
+		}
+
+		if (info->attrs[FOU_ATTR_PEER_V6]) {
+			attr = info->attrs[FOU_ATTR_PEER_V6];
+			cfg->udp_config.peer_ip6 = nla_get_in6_addr(attr);
+			has_peer = true;
+		}
+#endif
+	}
+
+	if (has_peer) {
+		if (info->attrs[FOU_ATTR_PEER_PORT]) {
+			port = nla_get_be16(info->attrs[FOU_ATTR_PEER_PORT]);
+			cfg->udp_config.peer_udp_port = port;
+		} else {
+			return -EINVAL;
+		}
+	}
+
+	if (info->attrs[FOU_ATTR_IFINDEX]) {
+		if (!has_local)
+			return -EINVAL;
+
+		ifindex = nla_get_s32(info->attrs[FOU_ATTR_IFINDEX]);
+
+		cfg->udp_config.bind_ifindex = ifindex;
+	}
+
 	return 0;
 }
 
@@ -702,15 +786,37 @@ static int fou_nl_cmd_rm_port(struct sk_buff *skb, struct genl_info *info)
 
 static int fou_fill_info(struct fou *fou, struct sk_buff *msg)
 {
+	struct sock *sk = fou->sock->sk;
+
 	if (nla_put_u8(msg, FOU_ATTR_AF, fou->sock->sk->sk_family) ||
 	    nla_put_be16(msg, FOU_ATTR_PORT, fou->port) ||
+	    nla_put_be16(msg, FOU_ATTR_PEER_PORT, sk->sk_dport) ||
 	    nla_put_u8(msg, FOU_ATTR_IPPROTO, fou->protocol) ||
-	    nla_put_u8(msg, FOU_ATTR_TYPE, fou->type))
+	    nla_put_u8(msg, FOU_ATTR_TYPE, fou->type) ||
+	    nla_put_s32(msg, FOU_ATTR_IFINDEX, sk->sk_bound_dev_if))
 		return -1;
 
 	if (fou->flags & FOU_F_REMCSUM_NOPARTIAL)
 		if (nla_put_flag(msg, FOU_ATTR_REMCSUM_NOPARTIAL))
 			return -1;
+
+	if (fou->sock->sk->sk_family == AF_INET) {
+		if (nla_put_in_addr(msg, FOU_ATTR_LOCAL_V4, sk->sk_rcv_saddr))
+			return -1;
+
+		if (nla_put_in_addr(msg, FOU_ATTR_PEER_V4, sk->sk_daddr))
+			return -1;
+#if IS_ENABLED(CONFIG_IPV6)
+	} else {
+		if (nla_put_in6_addr(msg, FOU_ATTR_LOCAL_V6,
+				     &sk->sk_v6_rcv_saddr))
+			return -1;
+
+		if (nla_put_in6_addr(msg, FOU_ATTR_PEER_V6, &sk->sk_v6_daddr))
+			return -1;
+#endif
+	}
+
 	return 0;
 }
 
@@ -763,7 +869,7 @@ static int fou_nl_cmd_get_port(struct sk_buff *skb, struct genl_info *info)
 	ret = -ESRCH;
 	mutex_lock(&fn->fou_lock);
 	list_for_each_entry(fout, &fn->fou_list, list) {
-		if (port == fout->port && family == fout->family) {
+		if (fou_cfg_cmp(fout, &cfg)) {
 			ret = fou_dump_info(fout, info->snd_portid,
 					    info->snd_seq, 0, msg,
 					    info->genlhdr->cmd);