net: WireGuard secure network tunnel

WireGuard is a layer 3 secure networking tunnel made specifically for
the kernel, that aims to be much simpler and easier to audit than IPsec.
Extensive documentation and description of the protocol and
considerations, along with formal proofs of the cryptography, are
available at:

  * https://www.wireguard.com/
  * https://www.wireguard.com/papers/wireguard.pdf

This commit implements WireGuard as a simple network device driver,
accessible in the usual RTNL way used by virtual network drivers. It
makes use of the udp_tunnel APIs, GRO, GSO, NAPI, and the usual set of
networking subsystem APIs. It has a somewhat novel multicore queueing
system designed for maximum throughput and minimal latency of encryption
operations, but it is implemented modestly using workqueues and NAPI.
Configuration is done via generic Netlink, and following a review from
the Netlink maintainer a year ago, several high profile userspace tools
have already implemented the API.

This commit also comes with several different tests, both in-kernel
tests and out-of-kernel tests based on network namespaces, taking profit
of the fact that sockets used by WireGuard intentionally stay in the
namespace the WireGuard interface was originally created, exactly like
the semantics of userspace tun devices. See wireguard.com/netns/ for
pictures and examples.

The source code is fairly short, but rather than combining everything
into a single file, WireGuard is developed as cleanly separable files,
making auditing and comprehension easier. Things are laid out as
follows:

  * noise.[ch], cookie.[ch], messages.h: These implement the bulk of the
    cryptographic aspects of the protocol, and are mostly data-only in
    nature, taking in buffers of bytes and spitting out buffers of
    bytes. They also handle reference counting for their various shared
    pieces of data, like keys and key lists.

  * ratelimiter.[ch]: Used as an integral part of cookie.[ch] for
    ratelimiting certain types of cryptographic operations in accordance
    with particular WireGuard semantics.

  * allowedips.[ch], peerlookup.[ch]: The main lookup structures of
    WireGuard, the former being trie-like with particular semantics, an
    integral part of the design of the protocol, and the latter just
    being nice helper functions around the various hashtables we use.

  * device.[ch]: Implementation of functions for the netdevice and for
    rtnl, responsible for maintaining the life of a given interface and
    wiring it up to the rest of WireGuard.

  * peer.[ch]: Each interface has a list of peers, with helper functions
    available here for creation, destruction, and reference counting.

  * socket.[ch]: Implementation of functions related to udp_socket and
    the general set of kernel socket APIs, for sending and receiving
    ciphertext UDP packets, and taking care of WireGuard-specific sticky
    socket routing semantics for the automatic roaming.

  * netlink.[ch]: Userspace API entry point for configuring WireGuard
    peers and devices. The API has been implemented by several userspace
    tools and network management utility, and the WireGuard project
    distributes the basic wg(8) tool.

  * queueing.[ch]: Shared function on the rx and tx path for handling
    the various queues used in the multicore algorithms.

  * send.c: Handles encrypting outgoing packets in parallel on
    multiple cores, before sending them in order on a single core, via
    workqueues and ring buffers. Also handles sending handshake and cookie
    messages as part of the protocol, in parallel.

  * receive.c: Handles decrypting incoming packets in parallel on
    multiple cores, before passing them off in order to be ingested via
    the rest of the networking subsystem with GRO via the typical NAPI
    poll function. Also handles receiving handshake and cookie messages
    as part of the protocol, in parallel.

  * timers.[ch]: Uses the timer wheel to implement protocol particular
    event timeouts, and gives a set of very simple event-driven entry
    point functions for callers.

  * main.c, version.h: Initialization and deinitialization of the module.

  * selftest/*.h: Runtime unit tests for some of the most security
    sensitive functions.

  * tools/testing/selftests/wireguard/netns.sh: Aforementioned testing
    script using network namespaces.

This commit aims to be as self-contained as possible, implementing
WireGuard as a standalone module not needing much special handling or
coordination from the network subsystem. I expect for future
optimizations to the network stack to positively improve WireGuard, and
vice-versa, but for the time being, this exists as intentionally
standalone.

We introduce a menu option for CONFIG_WIREGUARD, as well as providing a
verbose debug log and self-tests via CONFIG_WIREGUARD_DEBUG.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: David Miller <davem@davemloft.net>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 240 insertions, 0 deletions

diff --git a/drivers/net/wireguard/peer.c b/drivers/net/wireguard/peer.c
new file mode 100644
index 000000000000..071eedf33f5a
--- /dev/null
+++ b/drivers/net/wireguard/peer.c
@@ -0,0 +1,240 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#include "peer.h"
+#include "device.h"
+#include "queueing.h"
+#include "timers.h"
+#include "peerlookup.h"
+#include "noise.h"
+
+#include <linux/kref.h>
+#include <linux/lockdep.h>
+#include <linux/rcupdate.h>
+#include <linux/list.h>
+
+static atomic64_t peer_counter = ATOMIC64_INIT(0);
+
+struct wg_peer *wg_peer_create(struct wg_device *wg,
+			       const u8 public_key[NOISE_PUBLIC_KEY_LEN],
+			       const u8 preshared_key[NOISE_SYMMETRIC_KEY_LEN])
+{
+	struct wg_peer *peer;
+	int ret = -ENOMEM;
+
+	lockdep_assert_held(&wg->device_update_lock);
+
+	if (wg->num_peers >= MAX_PEERS_PER_DEVICE)
+		return ERR_PTR(ret);
+
+	peer = kzalloc(sizeof(*peer), GFP_KERNEL);
+	if (unlikely(!peer))
+		return ERR_PTR(ret);
+	peer->device = wg;
+
+	if (!wg_noise_handshake_init(&peer->handshake, &wg->static_identity,
+				     public_key, preshared_key, peer)) {
+		ret = -EKEYREJECTED;
+		goto err_1;
+	}
+	if (dst_cache_init(&peer->endpoint_cache, GFP_KERNEL))
+		goto err_1;
+	if (wg_packet_queue_init(&peer->tx_queue, wg_packet_tx_worker, false,
+				 MAX_QUEUED_PACKETS))
+		goto err_2;
+	if (wg_packet_queue_init(&peer->rx_queue, NULL, false,
+				 MAX_QUEUED_PACKETS))
+		goto err_3;
+
+	peer->internal_id = atomic64_inc_return(&peer_counter);
+	peer->serial_work_cpu = nr_cpumask_bits;
+	wg_cookie_init(&peer->latest_cookie);
+	wg_timers_init(peer);
+	wg_cookie_checker_precompute_peer_keys(peer);
+	spin_lock_init(&peer->keypairs.keypair_update_lock);
+	INIT_WORK(&peer->transmit_handshake_work,
+		  wg_packet_handshake_send_worker);
+	rwlock_init(&peer->endpoint_lock);
+	kref_init(&peer->refcount);
+	skb_queue_head_init(&peer->staged_packet_queue);
+	wg_noise_reset_last_sent_handshake(&peer->last_sent_handshake);
+	set_bit(NAPI_STATE_NO_BUSY_POLL, &peer->napi.state);
+	netif_napi_add(wg->dev, &peer->napi, wg_packet_rx_poll,
+		       NAPI_POLL_WEIGHT);
+	napi_enable(&peer->napi);
+	list_add_tail(&peer->peer_list, &wg->peer_list);
+	INIT_LIST_HEAD(&peer->allowedips_list);
+	wg_pubkey_hashtable_add(wg->peer_hashtable, peer);
+	++wg->num_peers;
+	pr_debug("%s: Peer %llu created\n", wg->dev->name, peer->internal_id);
+	return peer;
+
+err_3:
+	wg_packet_queue_free(&peer->tx_queue, false);
+err_2:
+	dst_cache_destroy(&peer->endpoint_cache);
+err_1:
+	kfree(peer);
+	return ERR_PTR(ret);
+}
+
+struct wg_peer *wg_peer_get_maybe_zero(struct wg_peer *peer)
+{
+	RCU_LOCKDEP_WARN(!rcu_read_lock_bh_held(),
+			 "Taking peer reference without holding the RCU read lock");
+	if (unlikely(!peer || !kref_get_unless_zero(&peer->refcount)))
+		return NULL;
+	return peer;
+}
+
+static void peer_make_dead(struct wg_peer *peer)
+{
+	/* Remove from configuration-time lookup structures. */
+	list_del_init(&peer->peer_list);
+	wg_allowedips_remove_by_peer(&peer->device->peer_allowedips, peer,
+				     &peer->device->device_update_lock);
+	wg_pubkey_hashtable_remove(peer->device->peer_hashtable, peer);
+
+	/* Mark as dead, so that we don't allow jumping contexts after. */
+	WRITE_ONCE(peer->is_dead, true);
+
+	/* The caller must now synchronize_rcu() for this to take effect. */
+}
+
+static void peer_remove_after_dead(struct wg_peer *peer)
+{
+	WARN_ON(!peer->is_dead);
+
+	/* No more keypairs can be created for this peer, since is_dead protects
+	 * add_new_keypair, so we can now destroy existing ones.
+	 */
+	wg_noise_keypairs_clear(&peer->keypairs);
+
+	/* Destroy all ongoing timers that were in-flight at the beginning of
+	 * this function.
+	 */
+	wg_timers_stop(peer);
+
+	/* The transition between packet encryption/decryption queues isn't
+	 * guarded by is_dead, but each reference's life is strictly bounded by
+	 * two generations: once for parallel crypto and once for serial
+	 * ingestion, so we can simply flush twice, and be sure that we no
+	 * longer have references inside these queues.
+	 */
+
+	/* a) For encrypt/decrypt. */
+	flush_workqueue(peer->device->packet_crypt_wq);
+	/* b.1) For send (but not receive, since that's napi). */
+	flush_workqueue(peer->device->packet_crypt_wq);
+	/* b.2.1) For receive (but not send, since that's wq). */
+	napi_disable(&peer->napi);
+	/* b.2.1) It's now safe to remove the napi struct, which must be done
+	 * here from process context.
+	 */
+	netif_napi_del(&peer->napi);
+
+	/* Ensure any workstructs we own (like transmit_handshake_work or
+	 * clear_peer_work) no longer are in use.
+	 */
+	flush_workqueue(peer->device->handshake_send_wq);
+
+	/* After the above flushes, a peer might still be active in a few
+	 * different contexts: 1) from xmit(), before hitting is_dead and
+	 * returning, 2) from wg_packet_consume_data(), before hitting is_dead
+	 * and returning, 3) from wg_receive_handshake_packet() after a point
+	 * where it has processed an incoming handshake packet, but where
+	 * all calls to pass it off to timers fails because of is_dead. We won't
+	 * have new references in (1) eventually, because we're removed from
+	 * allowedips; we won't have new references in (2) eventually, because
+	 * wg_index_hashtable_lookup will always return NULL, since we removed
+	 * all existing keypairs and no more can be created; we won't have new
+	 * references in (3) eventually, because we're removed from the pubkey
+	 * hash table, which allows for a maximum of one handshake response,
+	 * via the still-uncleared index hashtable entry, but not more than one,
+	 * and in wg_cookie_message_consume, the lookup eventually gets a peer
+	 * with a refcount of zero, so no new reference is taken.
+	 */
+
+	--peer->device->num_peers;
+	wg_peer_put(peer);
+}
+
+/* We have a separate "remove" function make sure that all active places where
+ * a peer is currently operating will eventually come to an end and not pass
+ * their reference onto another context.
+ */
+void wg_peer_remove(struct wg_peer *peer)
+{
+	if (unlikely(!peer))
+		return;
+	lockdep_assert_held(&peer->device->device_update_lock);
+
+	peer_make_dead(peer);
+	synchronize_rcu();
+	peer_remove_after_dead(peer);
+}
+
+void wg_peer_remove_all(struct wg_device *wg)
+{
+	struct wg_peer *peer, *temp;
+	LIST_HEAD(dead_peers);
+
+	lockdep_assert_held(&wg->device_update_lock);
+
+	/* Avoid having to traverse individually for each one. */
+	wg_allowedips_free(&wg->peer_allowedips, &wg->device_update_lock);
+
+	list_for_each_entry_safe(peer, temp, &wg->peer_list, peer_list) {
+		peer_make_dead(peer);
+		list_add_tail(&peer->peer_list, &dead_peers);
+	}
+	synchronize_rcu();
+	list_for_each_entry_safe(peer, temp, &dead_peers, peer_list)
+		peer_remove_after_dead(peer);
+}
+
+static void rcu_release(struct rcu_head *rcu)
+{
+	struct wg_peer *peer = container_of(rcu, struct wg_peer, rcu);
+
+	dst_cache_destroy(&peer->endpoint_cache);
+	wg_packet_queue_free(&peer->rx_queue, false);
+	wg_packet_queue_free(&peer->tx_queue, false);
+
+	/* The final zeroing takes care of clearing any remaining handshake key
+	 * material and other potentially sensitive information.
+	 */
+	kzfree(peer);
+}
+
+static void kref_release(struct kref *refcount)
+{
+	struct wg_peer *peer = container_of(refcount, struct wg_peer, refcount);
+
+	pr_debug("%s: Peer %llu (%pISpfsc) destroyed\n",
+		 peer->device->dev->name, peer->internal_id,
+		 &peer->endpoint.addr);
+
+	/* Remove ourself from dynamic runtime lookup structures, now that the
+	 * last reference is gone.
+	 */
+	wg_index_hashtable_remove(peer->device->index_hashtable,
+				  &peer->handshake.entry);
+
+	/* Remove any lingering packets that didn't have a chance to be
+	 * transmitted.
+	 */
+	wg_packet_purge_staged_packets(peer);
+
+	/* Free the memory used. */
+	call_rcu(&peer->rcu, rcu_release);
+}
+
+void wg_peer_put(struct wg_peer *peer)
+{
+	if (unlikely(!peer))
+		return;
+	kref_put(&peer->refcount, kref_release);
+}