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, 381 insertions, 0 deletions

diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c
new file mode 100644
index 000000000000..72667d5399c3
--- /dev/null
+++ b/drivers/net/wireguard/allowedips.c
@@ -0,0 +1,381 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#include "allowedips.h"
+#include "peer.h"
+
+static void swap_endian(u8 *dst, const u8 *src, u8 bits)
+{
+	if (bits == 32) {
+		*(u32 *)dst = be32_to_cpu(*(const __be32 *)src);
+	} else if (bits == 128) {
+		((u64 *)dst)[0] = be64_to_cpu(((const __be64 *)src)[0]);
+		((u64 *)dst)[1] = be64_to_cpu(((const __be64 *)src)[1]);
+	}
+}
+
+static void copy_and_assign_cidr(struct allowedips_node *node, const u8 *src,
+				 u8 cidr, u8 bits)
+{
+	node->cidr = cidr;
+	node->bit_at_a = cidr / 8U;
+#ifdef __LITTLE_ENDIAN
+	node->bit_at_a ^= (bits / 8U - 1U) % 8U;
+#endif
+	node->bit_at_b = 7U - (cidr % 8U);
+	node->bitlen = bits;
+	memcpy(node->bits, src, bits / 8U);
+}
+#define CHOOSE_NODE(parent, key) \
+	parent->bit[(key[parent->bit_at_a] >> parent->bit_at_b) & 1]
+
+static void node_free_rcu(struct rcu_head *rcu)
+{
+	kfree(container_of(rcu, struct allowedips_node, rcu));
+}
+
+static void push_rcu(struct allowedips_node **stack,
+		     struct allowedips_node __rcu *p, unsigned int *len)
+{
+	if (rcu_access_pointer(p)) {
+		WARN_ON(IS_ENABLED(DEBUG) && *len >= 128);
+		stack[(*len)++] = rcu_dereference_raw(p);
+	}
+}
+
+static void root_free_rcu(struct rcu_head *rcu)
+{
+	struct allowedips_node *node, *stack[128] = {
+		container_of(rcu, struct allowedips_node, rcu) };
+	unsigned int len = 1;
+
+	while (len > 0 && (node = stack[--len])) {
+		push_rcu(stack, node->bit[0], &len);
+		push_rcu(stack, node->bit[1], &len);
+		kfree(node);
+	}
+}
+
+static void root_remove_peer_lists(struct allowedips_node *root)
+{
+	struct allowedips_node *node, *stack[128] = { root };
+	unsigned int len = 1;
+
+	while (len > 0 && (node = stack[--len])) {
+		push_rcu(stack, node->bit[0], &len);
+		push_rcu(stack, node->bit[1], &len);
+		if (rcu_access_pointer(node->peer))
+			list_del(&node->peer_list);
+	}
+}
+
+static void walk_remove_by_peer(struct allowedips_node __rcu **top,
+				struct wg_peer *peer, struct mutex *lock)
+{
+#define REF(p) rcu_access_pointer(p)
+#define DEREF(p) rcu_dereference_protected(*(p), lockdep_is_held(lock))
+#define PUSH(p) ({                                                             \
+		WARN_ON(IS_ENABLED(DEBUG) && len >= 128);                      \
+		stack[len++] = p;                                              \
+	})
+
+	struct allowedips_node __rcu **stack[128], **nptr;
+	struct allowedips_node *node, *prev;
+	unsigned int len;
+
+	if (unlikely(!peer || !REF(*top)))
+		return;
+
+	for (prev = NULL, len = 0, PUSH(top); len > 0; prev = node) {
+		nptr = stack[len - 1];
+		node = DEREF(nptr);
+		if (!node) {
+			--len;
+			continue;
+		}
+		if (!prev || REF(prev->bit[0]) == node ||
+		    REF(prev->bit[1]) == node) {
+			if (REF(node->bit[0]))
+				PUSH(&node->bit[0]);
+			else if (REF(node->bit[1]))
+				PUSH(&node->bit[1]);
+		} else if (REF(node->bit[0]) == prev) {
+			if (REF(node->bit[1]))
+				PUSH(&node->bit[1]);
+		} else {
+			if (rcu_dereference_protected(node->peer,
+				lockdep_is_held(lock)) == peer) {
+				RCU_INIT_POINTER(node->peer, NULL);
+				list_del_init(&node->peer_list);
+				if (!node->bit[0] || !node->bit[1]) {
+					rcu_assign_pointer(*nptr, DEREF(
+					       &node->bit[!REF(node->bit[0])]));
+					call_rcu(&node->rcu, node_free_rcu);
+					node = DEREF(nptr);
+				}
+			}
+			--len;
+		}
+	}
+
+#undef REF
+#undef DEREF
+#undef PUSH
+}
+
+static unsigned int fls128(u64 a, u64 b)
+{
+	return a ? fls64(a) + 64U : fls64(b);
+}
+
+static u8 common_bits(const struct allowedips_node *node, const u8 *key,
+		      u8 bits)
+{
+	if (bits == 32)
+		return 32U - fls(*(const u32 *)node->bits ^ *(const u32 *)key);
+	else if (bits == 128)
+		return 128U - fls128(
+			*(const u64 *)&node->bits[0] ^ *(const u64 *)&key[0],
+			*(const u64 *)&node->bits[8] ^ *(const u64 *)&key[8]);
+	return 0;
+}
+
+static bool prefix_matches(const struct allowedips_node *node, const u8 *key,
+			   u8 bits)
+{
+	/* This could be much faster if it actually just compared the common
+	 * bits properly, by precomputing a mask bswap(~0 << (32 - cidr)), and
+	 * the rest, but it turns out that common_bits is already super fast on
+	 * modern processors, even taking into account the unfortunate bswap.
+	 * So, we just inline it like this instead.
+	 */
+	return common_bits(node, key, bits) >= node->cidr;
+}
+
+static struct allowedips_node *find_node(struct allowedips_node *trie, u8 bits,
+					 const u8 *key)
+{
+	struct allowedips_node *node = trie, *found = NULL;
+
+	while (node && prefix_matches(node, key, bits)) {
+		if (rcu_access_pointer(node->peer))
+			found = node;
+		if (node->cidr == bits)
+			break;
+		node = rcu_dereference_bh(CHOOSE_NODE(node, key));
+	}
+	return found;
+}
+
+/* Returns a strong reference to a peer */
+static struct wg_peer *lookup(struct allowedips_node __rcu *root, u8 bits,
+			      const void *be_ip)
+{
+	/* Aligned so it can be passed to fls/fls64 */
+	u8 ip[16] __aligned(__alignof(u64));
+	struct allowedips_node *node;
+	struct wg_peer *peer = NULL;
+
+	swap_endian(ip, be_ip, bits);
+
+	rcu_read_lock_bh();
+retry:
+	node = find_node(rcu_dereference_bh(root), bits, ip);
+	if (node) {
+		peer = wg_peer_get_maybe_zero(rcu_dereference_bh(node->peer));
+		if (!peer)
+			goto retry;
+	}
+	rcu_read_unlock_bh();
+	return peer;
+}
+
+static bool node_placement(struct allowedips_node __rcu *trie, const u8 *key,
+			   u8 cidr, u8 bits, struct allowedips_node **rnode,
+			   struct mutex *lock)
+{
+	struct allowedips_node *node = rcu_dereference_protected(trie,
+						lockdep_is_held(lock));
+	struct allowedips_node *parent = NULL;
+	bool exact = false;
+
+	while (node && node->cidr <= cidr && prefix_matches(node, key, bits)) {
+		parent = node;
+		if (parent->cidr == cidr) {
+			exact = true;
+			break;
+		}
+		node = rcu_dereference_protected(CHOOSE_NODE(parent, key),
+						 lockdep_is_held(lock));
+	}
+	*rnode = parent;
+	return exact;
+}
+
+static int add(struct allowedips_node __rcu **trie, u8 bits, const u8 *key,
+	       u8 cidr, struct wg_peer *peer, struct mutex *lock)
+{
+	struct allowedips_node *node, *parent, *down, *newnode;
+
+	if (unlikely(cidr > bits || !peer))
+		return -EINVAL;
+
+	if (!rcu_access_pointer(*trie)) {
+		node = kzalloc(sizeof(*node), GFP_KERNEL);
+		if (unlikely(!node))
+			return -ENOMEM;
+		RCU_INIT_POINTER(node->peer, peer);
+		list_add_tail(&node->peer_list, &peer->allowedips_list);
+		copy_and_assign_cidr(node, key, cidr, bits);
+		rcu_assign_pointer(*trie, node);
+		return 0;
+	}
+	if (node_placement(*trie, key, cidr, bits, &node, lock)) {
+		rcu_assign_pointer(node->peer, peer);
+		list_move_tail(&node->peer_list, &peer->allowedips_list);
+		return 0;
+	}
+
+	newnode = kzalloc(sizeof(*newnode), GFP_KERNEL);
+	if (unlikely(!newnode))
+		return -ENOMEM;
+	RCU_INIT_POINTER(newnode->peer, peer);
+	list_add_tail(&newnode->peer_list, &peer->allowedips_list);
+	copy_and_assign_cidr(newnode, key, cidr, bits);
+
+	if (!node) {
+		down = rcu_dereference_protected(*trie, lockdep_is_held(lock));
+	} else {
+		down = rcu_dereference_protected(CHOOSE_NODE(node, key),
+						 lockdep_is_held(lock));
+		if (!down) {
+			rcu_assign_pointer(CHOOSE_NODE(node, key), newnode);
+			return 0;
+		}
+	}
+	cidr = min(cidr, common_bits(down, key, bits));
+	parent = node;
+
+	if (newnode->cidr == cidr) {
+		rcu_assign_pointer(CHOOSE_NODE(newnode, down->bits), down);
+		if (!parent)
+			rcu_assign_pointer(*trie, newnode);
+		else
+			rcu_assign_pointer(CHOOSE_NODE(parent, newnode->bits),
+					   newnode);
+	} else {
+		node = kzalloc(sizeof(*node), GFP_KERNEL);
+		if (unlikely(!node)) {
+			kfree(newnode);
+			return -ENOMEM;
+		}
+		INIT_LIST_HEAD(&node->peer_list);
+		copy_and_assign_cidr(node, newnode->bits, cidr, bits);
+
+		rcu_assign_pointer(CHOOSE_NODE(node, down->bits), down);
+		rcu_assign_pointer(CHOOSE_NODE(node, newnode->bits), newnode);
+		if (!parent)
+			rcu_assign_pointer(*trie, node);
+		else
+			rcu_assign_pointer(CHOOSE_NODE(parent, node->bits),
+					   node);
+	}
+	return 0;
+}
+
+void wg_allowedips_init(struct allowedips *table)
+{
+	table->root4 = table->root6 = NULL;
+	table->seq = 1;
+}
+
+void wg_allowedips_free(struct allowedips *table, struct mutex *lock)
+{
+	struct allowedips_node __rcu *old4 = table->root4, *old6 = table->root6;
+
+	++table->seq;
+	RCU_INIT_POINTER(table->root4, NULL);
+	RCU_INIT_POINTER(table->root6, NULL);
+	if (rcu_access_pointer(old4)) {
+		struct allowedips_node *node = rcu_dereference_protected(old4,
+							lockdep_is_held(lock));
+
+		root_remove_peer_lists(node);
+		call_rcu(&node->rcu, root_free_rcu);
+	}
+	if (rcu_access_pointer(old6)) {
+		struct allowedips_node *node = rcu_dereference_protected(old6,
+							lockdep_is_held(lock));
+
+		root_remove_peer_lists(node);
+		call_rcu(&node->rcu, root_free_rcu);
+	}
+}
+
+int wg_allowedips_insert_v4(struct allowedips *table, const struct in_addr *ip,
+			    u8 cidr, struct wg_peer *peer, struct mutex *lock)
+{
+	/* Aligned so it can be passed to fls */
+	u8 key[4] __aligned(__alignof(u32));
+
+	++table->seq;
+	swap_endian(key, (const u8 *)ip, 32);
+	return add(&table->root4, 32, key, cidr, peer, lock);
+}
+
+int wg_allowedips_insert_v6(struct allowedips *table, const struct in6_addr *ip,
+			    u8 cidr, struct wg_peer *peer, struct mutex *lock)
+{
+	/* Aligned so it can be passed to fls64 */
+	u8 key[16] __aligned(__alignof(u64));
+
+	++table->seq;
+	swap_endian(key, (const u8 *)ip, 128);
+	return add(&table->root6, 128, key, cidr, peer, lock);
+}
+
+void wg_allowedips_remove_by_peer(struct allowedips *table,
+				  struct wg_peer *peer, struct mutex *lock)
+{
+	++table->seq;
+	walk_remove_by_peer(&table->root4, peer, lock);
+	walk_remove_by_peer(&table->root6, peer, lock);
+}
+
+int wg_allowedips_read_node(struct allowedips_node *node, u8 ip[16], u8 *cidr)
+{
+	const unsigned int cidr_bytes = DIV_ROUND_UP(node->cidr, 8U);
+	swap_endian(ip, node->bits, node->bitlen);
+	memset(ip + cidr_bytes, 0, node->bitlen / 8U - cidr_bytes);
+	if (node->cidr)
+		ip[cidr_bytes - 1U] &= ~0U << (-node->cidr % 8U);
+
+	*cidr = node->cidr;
+	return node->bitlen == 32 ? AF_INET : AF_INET6;
+}
+
+/* Returns a strong reference to a peer */
+struct wg_peer *wg_allowedips_lookup_dst(struct allowedips *table,
+					 struct sk_buff *skb)
+{
+	if (skb->protocol == htons(ETH_P_IP))
+		return lookup(table->root4, 32, &ip_hdr(skb)->daddr);
+	else if (skb->protocol == htons(ETH_P_IPV6))
+		return lookup(table->root6, 128, &ipv6_hdr(skb)->daddr);
+	return NULL;
+}
+
+/* Returns a strong reference to a peer */
+struct wg_peer *wg_allowedips_lookup_src(struct allowedips *table,
+					 struct sk_buff *skb)
+{
+	if (skb->protocol == htons(ETH_P_IP))
+		return lookup(table->root4, 32, &ip_hdr(skb)->saddr);
+	else if (skb->protocol == htons(ETH_P_IPV6))
+		return lookup(table->root6, 128, &ipv6_hdr(skb)->saddr);
+	return NULL;
+}
+
+#include "selftest/allowedips.c"