[PATCH net-next v3 09/24] ovpn: implement basic TX path (UDP)

Antonio Quartulli
2024-05-06T01:15:43Z

Packets sent over the ovpn interface are processed and transmitted to the
connected peer, if any.

Implementation is UDP only. TCP will be added by a later patch.

Note: no crypto/encapsulation exists yet. packets are just captured and
sent.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
drivers/net/ovpn/io.c | 174 ++++++++++++++++++++++++++-
drivers/net/ovpn/io.h | 2 +
drivers/net/ovpn/main.c | 2 +
drivers/net/ovpn/ovpnstruct.h | 2 +
drivers/net/ovpn/peer.c | 37 ++++++
drivers/net/ovpn/peer.h | 9 ++
drivers/net/ovpn/udp.c | 219 ++++++++++++++++++++++++++++++++++
drivers/net/ovpn/udp.h | 14 +++
8 files changed, 458 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index a420bb45f25f..36cfb95edbf4 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -9,11 +9,13 @@

#include <linux/netdevice.h>
#include <linux/skbuff.h>
+#include <net/gso.h>

#include "io.h"
#include "ovpnstruct.h"
#include "netlink.h"
#include "peer.h"
+#include "udp.h"

int ovpn_struct_init(struct net_device *dev)
{
@@ -28,6 +30,12 @@ int ovpn_struct_init(struct net_device *dev)

spin_lock_init(&ovpn->lock);

+ ovpn->crypto_wq = alloc_workqueue("ovpn-crypto-wq-%s",
+ WQ_CPU_INTENSIVE | WQ_MEM_RECLAIM, 0,
+ dev->name);
+ if (!ovpn->crypto_wq)
+ return -ENOMEM;
+
ovpn->events_wq = alloc_workqueue("ovpn-events-wq-%s", WQ_MEM_RECLAIM,
0, dev->name);
if (!ovpn->events_wq)
@@ -40,11 +48,175 @@ int ovpn_struct_init(struct net_device *dev)
return 0;
}

+static bool ovpn_encrypt_one(struct ovpn_peer *peer, struct sk_buff *skb)
+{
+ return true;
+}
+
+/* Process packets in TX queue in a transport-specific way.
+ *
+ * UDP transport - encrypt and send across the tunnel.
+ */
+void ovpn_encrypt_work(struct work_struct *work)
+{
+ struct sk_buff *skb, *curr, *next;
+ struct ovpn_peer *peer;
+
+ peer = container_of(work, struct ovpn_peer, encrypt_work);
+ while ((skb = ptr_ring_consume_bh(&peer->tx_ring))) {
+ /* this might be a GSO-segmented skb list: process each skb
+ * independently
+ */
+ skb_list_walk_safe(skb, curr, next) {
+ /* if one segment fails encryption, we drop the entire
+ * packet, because it does not really make sense to send
+ * only part of it at this point
+ */
+ if (unlikely(!ovpn_encrypt_one(peer, curr))) {
+ kfree_skb_list(skb);
+ skb = NULL;
+ break;
+ }
+ }
+
+ /* successful encryption */
+ if (likely(skb)) {
+ skb_list_walk_safe(skb, curr, next) {
+ skb_mark_not_on_list(curr);
+
+ switch (peer->sock->sock->sk->sk_protocol) {
+ case IPPROTO_UDP:
+ ovpn_udp_send_skb(peer->ovpn, peer,
+ curr);
+ break;
+ default:
+ /* no transport configured yet */
+ consume_skb(skb);
+ break;
+ }
+ }
+ }
+
+ /* give a chance to be rescheduled if needed */
+ cond_resched();
+ }
+ ovpn_peer_put(peer);
+}
+
+/* send skb to connected peer, if any */
+static void ovpn_queue_skb(struct ovpn_struct *ovpn, struct sk_buff *skb,
+ struct ovpn_peer *peer)
+{
+ int ret;
+
+ if (likely(!peer))
+ /* retrieve peer serving the destination IP of this packet */
+ peer = ovpn_peer_get_by_dst(ovpn, skb);
+ if (unlikely(!peer)) {
+ net_dbg_ratelimited("%s: no peer to send data to\n",
+ ovpn->dev->name);
+ goto drop;
+ }
+
+ ret = ptr_ring_produce_bh(&peer->tx_ring, skb);
+ if (unlikely(ret < 0)) {
+ net_err_ratelimited("%s: cannot queue packet to TX ring\n",
+ peer->ovpn->dev->name);
+ goto drop;
+ }
+
+ if (!queue_work(ovpn->crypto_wq, &peer->encrypt_work))
+ ovpn_peer_put(peer);
+
+ return;
+drop:
+ if (peer)
+ ovpn_peer_put(peer);
+ kfree_skb_list(skb);
+}
+
+/* Return IP protocol version from skb header.
+ * Return 0 if protocol is not IPv4/IPv6 or cannot be read.
+ */
+static __be16 ovpn_ip_check_protocol(struct sk_buff *skb)
+{
+ __be16 proto = 0;
+
+ /* skb could be non-linear, make sure IP header is in non-fragmented
+ * part
+ */
+ if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
+ return 0;
+
+ if (ip_hdr(skb)->version == 4)
+ proto = htons(ETH_P_IP);
+ else if (ip_hdr(skb)->version == 6)
+ proto = htons(ETH_P_IPV6);
+
+ return proto;
+}
+
/* Send user data to the network
*/
netdev_tx_t ovpn_net_xmit(struct sk_buff *skb, struct net_device *dev)
{
+ struct ovpn_struct *ovpn = netdev_priv(dev);
+ struct sk_buff *segments, *tmp, *curr, *next;
+ struct sk_buff_head skb_list;
+ __be16 proto;
+ int ret;
+
+ /* reset netfilter state */
+ nf_reset_ct(skb);
+
+ /* verify IP header size in network packet */
+ proto = ovpn_ip_check_protocol(skb);
+ if (unlikely(!proto || skb->protocol != proto)) {
+ net_err_ratelimited("%s: dropping malformed payload packet\n",
+ dev->name);
+ goto drop;
+ }
+
+ if (skb_is_gso(skb)) {
+ segments = skb_gso_segment(skb, 0);
+ if (IS_ERR(segments)) {
+ ret = PTR_ERR(segments);
+ net_err_ratelimited("%s: cannot segment packet: %d\n",
+ dev->name, ret);
+ goto drop;
+ }
+
+ consume_skb(skb);
+ skb = segments;
+ }
+
+ /* from this moment on, "skb" might be a list */
+
+ __skb_queue_head_init(&skb_list);
+ skb_list_walk_safe(skb, curr, next) {
+ skb_mark_not_on_list(curr);
+
+ tmp = skb_share_check(curr, GFP_ATOMIC);
+ if (unlikely(!tmp)) {
+ kfree_skb_list(next);
+ net_err_ratelimited("%s: skb_share_check failed\n",
+ dev->name);
+ goto drop_list;
+ }
+
+ __skb_queue_tail(&skb_list, tmp);
+ }
+ skb_list.prev->next = NULL;
+
+ ovpn_queue_skb(ovpn, skb_list.next, NULL);
+
+ return NETDEV_TX_OK;
+
+drop_list:
+ skb_queue_walk_safe(&skb_list, curr, next)
+ kfree_skb(curr);
+drop:
skb_tx_error(skb);
- kfree_skb(skb);
+ kfree_skb_list(skb);
return NET_XMIT_DROP;
}
diff --git a/drivers/net/ovpn/io.h b/drivers/net/ovpn/io.h
index 61a2485e16b5..171e87f584b6 100644
--- a/drivers/net/ovpn/io.h
+++ b/drivers/net/ovpn/io.h
@@ -19,4 +19,6 @@
int ovpn_struct_init(struct net_device *dev);
netdev_tx_t ovpn_net_xmit(struct sk_buff *skb, struct net_device *dev);

+void ovpn_encrypt_work(struct work_struct *work);
+
#endif /* _NET_OVPN_OVPN_H_ */
diff --git a/drivers/net/ovpn/main.c b/drivers/net/ovpn/main.c
index dba35ecb236b..9ae9844dd281 100644
--- a/drivers/net/ovpn/main.c
+++ b/drivers/net/ovpn/main.c
@@ -39,7 +39,9 @@ static void ovpn_struct_free(struct net_device *net)
rtnl_unlock();

free_percpu(net->tstats);
+ flush_workqueue(ovpn->crypto_wq);
flush_workqueue(ovpn->events_wq);
+ destroy_workqueue(ovpn->crypto_wq);
destroy_workqueue(ovpn->events_wq);
rcu_barrier();
}
diff --git a/drivers/net/ovpn/ovpnstruct.h b/drivers/net/ovpn/ovpnstruct.h
index b79d4f0474b0..7414c2459fb9 100644
--- a/drivers/net/ovpn/ovpnstruct.h
+++ b/drivers/net/ovpn/ovpnstruct.h
@@ -18,6 +18,7 @@
* @registered: whether dev is still registered with netdev or not
* @mode: device operation mode (i.e. p2p, mp, ..)
* @lock: protect this object
+ * @crypto_wq: used to schedule crypto work that may sleep during TX/RX
* @event_wq: used to schedule generic events that may sleep and that need to be
* performed outside of softirq context
* @peer: in P2P mode, this is the only remote peer
@@ -28,6 +29,7 @@ struct ovpn_struct {
bool registered;
enum ovpn_mode mode;
spinlock_t lock; /* protect writing to the ovpn_struct object */
+ struct workqueue_struct *crypto_wq;
struct workqueue_struct *events_wq;
struct ovpn_peer __rcu *peer;
struct list_head dev_list;
diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index 2948b7320d47..f023f919b75d 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -39,6 +39,8 @@ struct ovpn_peer *ovpn_peer_new(struct ovpn_struct *ovpn, u32 id)
spin_lock_init(&peer->lock);
kref_init(&peer->refcount);

+ INIT_WORK(&peer->encrypt_work, ovpn_encrypt_work);
+
ret = dst_cache_init(&peer->dst_cache, GFP_KERNEL);
if (ret < 0) {
netdev_err(ovpn->dev, "%s: cannot initialize dst cache\n",
@@ -119,6 +121,9 @@ static void ovpn_peer_release_rcu(struct rcu_head *head)

void ovpn_peer_release(struct ovpn_peer *peer)
{
+ if (peer->sock)
+ ovpn_socket_put(peer->sock);
+
call_rcu(&peer->rcu, ovpn_peer_release_rcu);
}

@@ -288,6 +293,38 @@ struct ovpn_peer *ovpn_peer_get_by_id(struct ovpn_struct *ovpn, u32 peer_id)
return peer;
}

+/**
+ * ovpn_peer_get_by_dst - Lookup peer to send skb to
+ * @ovpn: the private data representing the current VPN session
+ * @skb: the skb to extract the destination address from
+ *
+ * This function takes a tunnel packet and looks up the peer to send it to
+ * after encapsulation. The skb is expected to be the in-tunnel packet, without
+ * any OpenVPN related header.
+ *
+ * Assume that the IP header is accessible in the skb data.
+ *
+ * Return: the peer if found or NULL otherwise.
+ */
+struct ovpn_peer *ovpn_peer_get_by_dst(struct ovpn_struct *ovpn,
+ struct sk_buff *skb)
+{
+ struct ovpn_peer *tmp, *peer = NULL;
+
+ /* in P2P mode, no matter the destination, packets are always sent to
+ * the single peer listening on the other side
+ */
+ if (ovpn->mode == OVPN_MODE_P2P) {
+ rcu_read_lock();
+ tmp = rcu_dereference(ovpn->peer);
+ if (likely(tmp && ovpn_peer_hold(tmp)))
+ peer = tmp;
+ rcu_read_unlock();
+ }
+
+ return peer;
+}
+
/**
* ovpn_peer_add_p2p - add per to related tables in a P2P instance
* @ovpn: the instance to add the peer to
diff --git a/drivers/net/ovpn/peer.h b/drivers/net/ovpn/peer.h
index 659df320525c..f915afa260c3 100644
--- a/drivers/net/ovpn/peer.h
+++ b/drivers/net/ovpn/peer.h
@@ -11,6 +11,7 @@
#define _NET_OVPN_OVPNPEER_H_

#include "bind.h"
+#include "socket.h"

#include <linux/ptr_ring.h>
#include <net/dst_cache.h>
@@ -22,9 +23,12 @@
* @id: unique identifier
* @vpn_addrs.ipv4: IPv4 assigned to peer on the tunnel
* @vpn_addrs.ipv6: IPv6 assigned to peer on the tunnel
+ * @encrypt_work: work used to process outgoing packets
+ * @decrypt_work: work used to process incoming packets
* @tx_ring: queue of outgoing poackets to this peer
* @rx_ring: queue of incoming packets from this peer
* @netif_rx_ring: queue of packets to be sent to the netdevice via NAPI
+ * @sock: the socket being used to talk to this peer
* @dst_cache: cache for dst_entry used to send to peer
* @bind: remote peer binding
* @halt: true if ovpn_peer_mark_delete was called
@@ -41,9 +45,12 @@ struct ovpn_peer {
struct in_addr ipv4;
struct in6_addr ipv6;
} vpn_addrs;
+ struct work_struct encrypt_work;
+ struct work_struct decrypt_work;
struct ptr_ring tx_ring;
struct ptr_ring rx_ring;
struct ptr_ring netif_rx_ring;
+ struct ovpn_socket *sock;
struct dst_cache dst_cache;
struct ovpn_bind __rcu *bind;
bool halt;
@@ -148,5 +155,7 @@ struct ovpn_peer *ovpn_peer_get_by_transp_addr(struct ovpn_struct *ovpn,
* Return: a pointer to the peer if found or NULL otherwise
*/
struct ovpn_peer *ovpn_peer_get_by_id(struct ovpn_struct *ovpn, u32 peer_id);
+struct ovpn_peer *ovpn_peer_get_by_dst(struct ovpn_struct *ovpn,
+ struct sk_buff *skb);

#endif /* _NET_OVPN_OVPNPEER_H_ */
diff --git a/drivers/net/ovpn/udp.c b/drivers/net/ovpn/udp.c
index 4b7d96a13df0..f434da76dc0a 100644
--- a/drivers/net/ovpn/udp.c
+++ b/drivers/net/ovpn/udp.c
@@ -7,13 +7,232 @@
*/

#include <linux/netdevice.h>
+#include <linux/inetdevice.h>
#include <linux/socket.h>
+#include <net/addrconf.h>
+#include <net/dst_cache.h>
+#include <net/route.h>
+#include <net/ipv6_stubs.h>
+#include <net/udp_tunnel.h>

#include "ovpnstruct.h"
#include "main.h"
+#include "bind.h"
+#include "io.h"
+#include "peer.h"
#include "socket.h"
#include "udp.h"

+/**
+ * ovpn_udp4_output - send IPv4 packet over udp socket
+ * @ovpn: the openvpn instance
+ * @bind: the binding related to the destination peer
+ * @cache: dst cache
+ * @sk: the socket to send the packet over
+ * @skb: the packet to send
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+static int ovpn_udp4_output(struct ovpn_struct *ovpn, struct ovpn_bind *bind,
+ struct dst_cache *cache, struct sock *sk,
+ struct sk_buff *skb)
+{
+ struct rtable *rt;
+ struct flowi4 fl = {
+ .saddr = bind->local.ipv4.s_addr,
+ .daddr = bind->sa.in4.sin_addr.s_addr,
+ .fl4_sport = inet_sk(sk)->inet_sport,
+ .fl4_dport = bind->sa.in4.sin_port,
+ .flowi4_proto = sk->sk_protocol,
+ .flowi4_mark = sk->sk_mark,
+ };
+ int ret;
+
+ local_bh_disable();
+ rt = dst_cache_get_ip4(cache, &fl.saddr);
+ if (rt)
+ goto transmit;
+
+ if (unlikely(!inet_confirm_addr(sock_net(sk), NULL, 0, fl.saddr,
+ RT_SCOPE_HOST))) {
+ /* we may end up here when the cached address is not usable
+ * anymore. In this case we reset address/cache and perform a
+ * new look up
+ */
+ fl.saddr = 0;
+ bind->local.ipv4.s_addr = 0;
+ dst_cache_reset(cache);
+ }
+
+ rt = ip_route_output_flow(sock_net(sk), &fl, sk);
+ if (IS_ERR(rt) && PTR_ERR(rt) == -EINVAL) {
+ fl.saddr = 0;
+ bind->local.ipv4.s_addr = 0;
+ dst_cache_reset(cache);
+
+ rt = ip_route_output_flow(sock_net(sk), &fl, sk);
+ }
+
+ if (IS_ERR(rt)) {
+ ret = PTR_ERR(rt);
+ net_dbg_ratelimited("%s: no route to host %pISpc: %d\n",
+ ovpn->dev->name, &bind->sa.in4, ret);
+ goto err;
+ }
+ dst_cache_set_ip4(cache, &rt->dst, fl.saddr);
+
+transmit:
+ udp_tunnel_xmit_skb(rt, sk, skb, fl.saddr, fl.daddr, 0,
+ ip4_dst_hoplimit(&rt->dst), 0, fl.fl4_sport,
+ fl.fl4_dport, false, sk->sk_no_check_tx);
+ ret = 0;
+err:
+ local_bh_enable();
+ return ret;
+}
+
+#if IS_ENABLED(CONFIG_IPV6)
+/**
+ * ovpn_udp6_output - send IPv6 packet over udp socket
+ * @ovpn: the openvpn instance
+ * @bind: the binding related to the destination peer
+ * @cache: dst cache
+ * @sk: the socket to send the packet over
+ * @skb: the packet to send
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+static int ovpn_udp6_output(struct ovpn_struct *ovpn, struct ovpn_bind *bind,
+ struct dst_cache *cache, struct sock *sk,
+ struct sk_buff *skb)
+{
+ struct dst_entry *dst;
+ int ret;
+
+ struct flowi6 fl = {
+ .saddr = bind->local.ipv6,
+ .daddr = bind->sa.in6.sin6_addr,
+ .fl6_sport = inet_sk(sk)->inet_sport,
+ .fl6_dport = bind->sa.in6.sin6_port,
+ .flowi6_proto = sk->sk_protocol,
+ .flowi6_mark = sk->sk_mark,
+ .flowi6_oif = bind->sa.in6.sin6_scope_id,
+ };
+
+ local_bh_disable();
+ dst = dst_cache_get_ip6(cache, &fl.saddr);
+ if (dst)
+ goto transmit;
+
+ if (unlikely(!ipv6_chk_addr(sock_net(sk), &fl.saddr, NULL, 0))) {
+ /* we may end up here when the cached address is not usable
+ * anymore. In this case we reset address/cache and perform a
+ * new look up
+ */
+ fl.saddr = in6addr_any;
+ bind->local.ipv6 = in6addr_any;
+ dst_cache_reset(cache);
+ }
+
+ dst = ipv6_stub->ipv6_dst_lookup_flow(sock_net(sk), sk, &fl, NULL);
+ if (IS_ERR(dst)) {
+ ret = PTR_ERR(dst);
+ net_dbg_ratelimited("%s: no route to host %pISpc: %d\n",
+ ovpn->dev->name, &bind->sa.in6, ret);
+ goto err;
+ }
+ dst_cache_set_ip6(cache, dst, &fl.saddr);
+
+transmit:
+ udp_tunnel6_xmit_skb(dst, sk, skb, skb->dev, &fl.saddr, &fl.daddr, 0,
+ ip6_dst_hoplimit(dst), 0, fl.fl6_sport,
+ fl.fl6_dport, udp_get_no_check6_tx(sk));
+ ret = 0;
+err:
+ local_bh_enable();
+ return ret;
+}
+#endif
+
+/**
+ * ovpn_udp_output - transmit skb using udp-tunnel
+ * @ovpn: the openvpn instance
+ * @bind: the binding related to the destination peer
+ * @cache: dst cache
+ * @sk: the socket to send the packet over
+ * @skb: the packet to send
+ *
+ * rcu_read_lock should be held on entry.
+ * On return, the skb is consumed.
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+static int ovpn_udp_output(struct ovpn_struct *ovpn, struct ovpn_bind *bind,
+ struct dst_cache *cache, struct sock *sk,
+ struct sk_buff *skb)
+{
+ int ret;
+
+ /* set sk to null if skb is already orphaned */
+ if (!skb->destructor)
+ skb->sk = NULL;
+
+ /* always permit openvpn-created packets to be (outside) fragmented */
+ skb->ignore_df = 1;
+
+ switch (bind->sa.in4.sin_family) {
+ case AF_INET:
+ ret = ovpn_udp4_output(ovpn, bind, cache, sk, skb);
+ break;
+#if IS_ENABLED(CONFIG_IPV6)
+ case AF_INET6:
+ ret = ovpn_udp6_output(ovpn, bind, cache, sk, skb);
+ break;
+#endif
+ default:
+ ret = -EAFNOSUPPORT;
+ break;
+ }
+
+ return ret;
+}
+
+void ovpn_udp_send_skb(struct ovpn_struct *ovpn, struct ovpn_peer *peer,
+ struct sk_buff *skb)
+{
+ struct ovpn_bind *bind;
+ struct socket *sock;
+ int ret = -1;
+
+ skb->dev = ovpn->dev;
+ /* no checksum performed at this layer */
+ skb->ip_summed = CHECKSUM_NONE;
+
+ /* get socket info */
+ sock = peer->sock->sock;
+ if (unlikely(!sock)) {
+ net_warn_ratelimited("%s: no sock for remote peer\n", __func__);
+ goto out;
+ }
+
+ rcu_read_lock();
+ /* get binding */
+ bind = rcu_dereference(peer->bind);
+ if (unlikely(!bind)) {
+ net_warn_ratelimited("%s: no bind for remote peer\n", __func__);
+ goto out_unlock;
+ }
+
+ /* crypto layer -> transport (UDP) */
+ ret = ovpn_udp_output(ovpn, bind, &peer->dst_cache, sock->sk, skb);
+
+out_unlock:
+ rcu_read_unlock();
+out:
+ if (ret < 0)
+ kfree_skb(skb);
+}
+
int ovpn_udp_socket_attach(struct socket *sock, struct ovpn_struct *ovpn)
{
struct ovpn_socket *old_data;
diff --git a/drivers/net/ovpn/udp.h b/drivers/net/ovpn/udp.h
index 16422a649cb9..f4eb1e63e103 100644
--- a/drivers/net/ovpn/udp.h
+++ b/drivers/net/ovpn/udp.h
@@ -9,7 +9,12 @@
#ifndef _NET_OVPN_UDP_H_
#define _NET_OVPN_UDP_H_

+#include <linux/skbuff.h>
+#include <net/sock.h>
+
+struct ovpn_peer;
struct ovpn_struct;
+struct sk_buff;
struct socket;

/**
@@ -24,4 +29,13 @@ struct socket;
*/
int ovpn_udp_socket_attach(struct socket *sock, struct ovpn_struct *ovpn);

+/**
+ * ovpn_udp_send_skb - prepare skb and send it over via UDP
+ * @ovpn: the openvpn instance
+ * @peer: the destination peer
+ * @skb: the packet to send
+ */
+void ovpn_udp_send_skb(struct ovpn_struct *ovpn, struct ovpn_peer *peer,
+ struct sk_buff *skb);
+
#endif /* _NET_OVPN_UDP_H_ */
--
2.43.2