In a multi-peer scenario there are a number of situations when a specific peer needs to be looked up.
We may want to lookup a peer by: 1. its ID 2. its VPN destination IP 3. its transport IP/port couple
For each of the above, there is a specific routing table referencing all peers for fast look up.
Case 2. is a bit special in the sense that an outgoing packet may not be sent to the peer VPN IP directly, but rather to a network behind it. For this reason we first perform a nexthop lookup in the system routing table and then we use the retrieved nexthop as peer search key.
Signed-off-by: Antonio Quartulli antonio@openvpn.net --- drivers/net/ovpn/peer.c | 272 ++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 264 insertions(+), 8 deletions(-)
diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c index 73ef509faab9701192a45ffe78a46dbbbeab01c2..c7dc9032c2b55fd42befc1f3e7a0eca893a96576 100644 --- a/drivers/net/ovpn/peer.c +++ b/drivers/net/ovpn/peer.c @@ -10,6 +10,7 @@ #include <linux/skbuff.h> #include <linux/list.h> #include <linux/hashtable.h> +#include <net/ip6_route.h>
#include "ovpnstruct.h" #include "bind.h" @@ -125,6 +126,94 @@ static bool ovpn_peer_skb_to_sockaddr(struct sk_buff *skb, return true; }
+/** + * ovpn_nexthop_from_skb4 - retrieve IPv4 nexthop for outgoing skb + * @skb: the outgoing packet + * + * Return: the IPv4 of the nexthop + */ +static __be32 ovpn_nexthop_from_skb4(struct sk_buff *skb) +{ + const struct rtable *rt = skb_rtable(skb); + + if (rt && rt->rt_uses_gateway) + return rt->rt_gw4; + + return ip_hdr(skb)->daddr; +} + +/** + * ovpn_nexthop_from_skb6 - retrieve IPv6 nexthop for outgoing skb + * @skb: the outgoing packet + * + * Return: the IPv6 of the nexthop + */ +static struct in6_addr ovpn_nexthop_from_skb6(struct sk_buff *skb) +{ + const struct rt6_info *rt = skb_rt6_info(skb); + + if (!rt || !(rt->rt6i_flags & RTF_GATEWAY)) + return ipv6_hdr(skb)->daddr; + + return rt->rt6i_gateway; +} + +#define ovpn_get_hash_head(_tbl, _key, _key_len) ({ \ + typeof(_tbl) *__tbl = &(_tbl); \ + (&(*__tbl)[jhash(_key, _key_len, 0) % HASH_SIZE(*__tbl)]); }) \ + +/** + * ovpn_peer_get_by_vpn_addr4 - retrieve peer by its VPN IPv4 address + * @ovpn: the openvpn instance to search + * @addr: VPN IPv4 to use as search key + * + * Refcounter is not increased for the returned peer. + * + * Return: the peer if found or NULL otherwise + */ +static struct ovpn_peer *ovpn_peer_get_by_vpn_addr4(struct ovpn_struct *ovpn, + __be32 addr) +{ + struct hlist_nulls_head *nhead; + struct hlist_nulls_node *ntmp; + struct ovpn_peer *tmp; + + nhead = ovpn_get_hash_head(ovpn->peers->by_vpn_addr, &addr, + sizeof(addr)); + + hlist_nulls_for_each_entry_rcu(tmp, ntmp, nhead, hash_entry_addr4) + if (addr == tmp->vpn_addrs.ipv4.s_addr) + return tmp; + + return NULL; +} + +/** + * ovpn_peer_get_by_vpn_addr6 - retrieve peer by its VPN IPv6 address + * @ovpn: the openvpn instance to search + * @addr: VPN IPv6 to use as search key + * + * Refcounter is not increased for the returned peer. + * + * Return: the peer if found or NULL otherwise + */ +static struct ovpn_peer *ovpn_peer_get_by_vpn_addr6(struct ovpn_struct *ovpn, + struct in6_addr *addr) +{ + struct hlist_nulls_head *nhead; + struct hlist_nulls_node *ntmp; + struct ovpn_peer *tmp; + + nhead = ovpn_get_hash_head(ovpn->peers->by_vpn_addr, addr, + sizeof(*addr)); + + hlist_nulls_for_each_entry_rcu(tmp, ntmp, nhead, hash_entry_addr6) + if (ipv6_addr_equal(addr, &tmp->vpn_addrs.ipv6)) + return tmp; + + return NULL; +} + /** * ovpn_peer_transp_match - check if sockaddr and peer binding match * @peer: the peer to get the binding from @@ -202,14 +291,44 @@ ovpn_peer_get_by_transp_addr_p2p(struct ovpn_struct *ovpn, struct ovpn_peer *ovpn_peer_get_by_transp_addr(struct ovpn_struct *ovpn, struct sk_buff *skb) { - struct ovpn_peer *peer = NULL; + struct ovpn_peer *tmp, *peer = NULL; struct sockaddr_storage ss = { 0 }; + struct hlist_nulls_head *nhead; + struct hlist_nulls_node *ntmp; + size_t sa_len;
if (unlikely(!ovpn_peer_skb_to_sockaddr(skb, &ss))) return NULL;
if (ovpn->mode == OVPN_MODE_P2P) - peer = ovpn_peer_get_by_transp_addr_p2p(ovpn, &ss); + return ovpn_peer_get_by_transp_addr_p2p(ovpn, &ss); + + switch (ss.ss_family) { + case AF_INET: + sa_len = sizeof(struct sockaddr_in); + break; + case AF_INET6: + sa_len = sizeof(struct sockaddr_in6); + break; + default: + return NULL; + } + + nhead = ovpn_get_hash_head(ovpn->peers->by_transp_addr, &ss, sa_len); + + rcu_read_lock(); + hlist_nulls_for_each_entry_rcu(tmp, ntmp, nhead, + hash_entry_transp_addr) { + if (!ovpn_peer_transp_match(tmp, &ss)) + continue; + + if (!ovpn_peer_hold(tmp)) + continue; + + peer = tmp; + break; + } + rcu_read_unlock();
return peer; } @@ -244,10 +363,27 @@ static struct ovpn_peer *ovpn_peer_get_by_id_p2p(struct ovpn_struct *ovpn, */ struct ovpn_peer *ovpn_peer_get_by_id(struct ovpn_struct *ovpn, u32 peer_id) { - struct ovpn_peer *peer = NULL; + struct ovpn_peer *tmp, *peer = NULL; + struct hlist_head *head;
if (ovpn->mode == OVPN_MODE_P2P) - peer = ovpn_peer_get_by_id_p2p(ovpn, peer_id); + return ovpn_peer_get_by_id_p2p(ovpn, peer_id); + + head = ovpn_get_hash_head(ovpn->peers->by_id, &peer_id, + sizeof(peer_id)); + + rcu_read_lock(); + hlist_for_each_entry_rcu(tmp, head, hash_entry_id) { + if (tmp->id != peer_id) + continue; + + if (!ovpn_peer_hold(tmp)) + continue; + + peer = tmp; + break; + } + rcu_read_unlock();
return peer; } @@ -269,6 +405,8 @@ struct ovpn_peer *ovpn_peer_get_by_dst(struct ovpn_struct *ovpn, struct sk_buff *skb) { struct ovpn_peer *peer = NULL; + struct in6_addr addr6; + __be32 addr4;
/* in P2P mode, no matter the destination, packets are always sent to * the single peer listening on the other side @@ -279,11 +417,109 @@ struct ovpn_peer *ovpn_peer_get_by_dst(struct ovpn_struct *ovpn, if (unlikely(peer && !ovpn_peer_hold(peer))) peer = NULL; rcu_read_unlock(); + return peer; }
+ rcu_read_lock(); + switch (skb_protocol_to_family(skb)) { + case AF_INET: + addr4 = ovpn_nexthop_from_skb4(skb); + peer = ovpn_peer_get_by_vpn_addr4(ovpn, addr4); + break; + case AF_INET6: + addr6 = ovpn_nexthop_from_skb6(skb); + peer = ovpn_peer_get_by_vpn_addr6(ovpn, &addr6); + break; + } + + if (unlikely(peer && !ovpn_peer_hold(peer))) + peer = NULL; + rcu_read_unlock(); + return peer; }
+/** + * ovpn_nexthop_from_rt4 - look up the IPv4 nexthop for the given destination + * @ovpn: the private data representing the current VPN session + * @dest: the destination to be looked up + * + * Looks up in the IPv4 system routing table the IP of the nexthop to be used + * to reach the destination passed as argument. If no nexthop can be found, the + * destination itself is returned as it probably has to be used as nexthop. + * + * Return: the IP of the next hop if found or dest itself otherwise + */ +static __be32 ovpn_nexthop_from_rt4(struct ovpn_struct *ovpn, __be32 dest) +{ + struct rtable *rt; + struct flowi4 fl = { + .daddr = dest + }; + + rt = ip_route_output_flow(dev_net(ovpn->dev), &fl, NULL); + if (IS_ERR(rt)) { + net_dbg_ratelimited("%s: no route to host %pI4\n", __func__, + &dest); + /* if we end up here this packet is probably going to be + * thrown away later + */ + return dest; + } + + if (!rt->rt_uses_gateway) + goto out; + + dest = rt->rt_gw4; +out: + ip_rt_put(rt); + return dest; +} + +/** + * ovpn_nexthop_from_rt6 - look up the IPv6 nexthop for the given destination + * @ovpn: the private data representing the current VPN session + * @dest: the destination to be looked up + * + * Looks up in the IPv6 system routing table the IP of the nexthop to be used + * to reach the destination passed as argument. If no nexthop can be found, the + * destination itself is returned as it probably has to be used as nexthop. + * + * Return: the IP of the next hop if found or dest itself otherwise + */ +static struct in6_addr ovpn_nexthop_from_rt6(struct ovpn_struct *ovpn, + struct in6_addr dest) +{ +#if IS_ENABLED(CONFIG_IPV6) + struct dst_entry *entry; + struct rt6_info *rt; + struct flowi6 fl = { + .daddr = dest, + }; + + entry = ipv6_stub->ipv6_dst_lookup_flow(dev_net(ovpn->dev), NULL, &fl, + NULL); + if (IS_ERR(entry)) { + net_dbg_ratelimited("%s: no route to host %pI6c\n", __func__, + &dest); + /* if we end up here this packet is probably going to be + * thrown away later + */ + return dest; + } + + rt = dst_rt6_info(entry); + + if (!(rt->rt6i_flags & RTF_GATEWAY)) + goto out; + + dest = rt->rt6i_gateway; +out: + dst_release((struct dst_entry *)rt); +#endif + return dest; +} + /** * ovpn_peer_check_by_src - check that skb source is routed via peer * @ovpn: the openvpn instance to search @@ -296,6 +532,8 @@ bool ovpn_peer_check_by_src(struct ovpn_struct *ovpn, struct sk_buff *skb, struct ovpn_peer *peer) { bool match = false; + struct in6_addr addr6; + __be32 addr4;
if (ovpn->mode == OVPN_MODE_P2P) { /* in P2P mode, no matter the destination, packets are always @@ -304,15 +542,33 @@ bool ovpn_peer_check_by_src(struct ovpn_struct *ovpn, struct sk_buff *skb, rcu_read_lock(); match = (peer == rcu_dereference(ovpn->peer)); rcu_read_unlock(); + return match; + } + + /* This function performs a reverse path check, therefore we now + * lookup the nexthop we would use if we wanted to route a packet + * to the source IP. If the nexthop matches the sender we know the + * latter is valid and we allow the packet to come in + */ + + switch (skb_protocol_to_family(skb)) { + case AF_INET: + addr4 = ovpn_nexthop_from_rt4(ovpn, ip_hdr(skb)->saddr); + rcu_read_lock(); + match = (peer == ovpn_peer_get_by_vpn_addr4(ovpn, addr4)); + rcu_read_unlock(); + break; + case AF_INET6: + addr6 = ovpn_nexthop_from_rt6(ovpn, ipv6_hdr(skb)->saddr); + rcu_read_lock(); + match = (peer == ovpn_peer_get_by_vpn_addr6(ovpn, &addr6)); + rcu_read_unlock(); + break; }
return match; }
-#define ovpn_get_hash_head(_tbl, _key, _key_len) ({ \ - typeof(_tbl) *__tbl = &(_tbl); \ - (&(*__tbl)[jhash(_key, _key_len, 0) % HASH_SIZE(*__tbl)]); }) \ - /** * ovpn_peer_add_mp - add peer to related tables in a MP instance * @ovpn: the instance to add the peer to