// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */

#include "queueing.h"
#include "timers.h"
#include "device.h"
#include "peer.h"
#include "socket.h"
#include "messages.h"
#include "cookie.h"

#include <linux/uio.h>
#include <linux/inetdevice.h>
#include <linux/socket.h>
#include <net/ip_tunnels.h>
#include <net/udp.h>
#include <net/sock.h>

static void wg_packet_send_handshake_initiation(struct wg_peer *peer)
{
        struct message_handshake_initiation packet;

        if (!wg_birthdate_has_expired(atomic64_read(&peer->last_sent_handshake),
                                      REKEY_TIMEOUT))
                return; /* This function is rate limited. */

        atomic64_set(&peer->last_sent_handshake, ktime_get_coarse_boottime_ns());
        net_dbg_ratelimited("%s: Sending handshake initiation to peer %llu (%pISpfsc)\n",
                            peer->device->dev->name, peer->internal_id,
                            &peer->endpoint.addr);

        if (wg_noise_handshake_create_initiation(&packet, &peer->handshake)) {
                wg_cookie_add_mac_to_packet(&packet, sizeof(packet), peer);
                wg_timers_any_authenticated_packet_traversal(peer);
                wg_timers_any_authenticated_packet_sent(peer);
                atomic64_set(&peer->last_sent_handshake,
                             ktime_get_coarse_boottime_ns());
                wg_socket_send_buffer_to_peer(peer, &packet, sizeof(packet),
                                              HANDSHAKE_DSCP);
                wg_timers_handshake_initiated(peer);
        }
}

void wg_packet_handshake_send_worker(struct work_struct *work)
{
        struct wg_peer *peer = container_of(work, struct wg_peer,
                                            transmit_handshake_work);

        wg_packet_send_handshake_initiation(peer);
        wg_peer_put(peer);
}

void wg_packet_send_queued_handshake_initiation(struct wg_peer *peer,
                                                bool is_retry)
{
        if (!is_retry)
                peer->timer_handshake_attempts = 0;

        rcu_read_lock_bh();
        /* We check last_sent_handshake here in addition to the actual function
         * we're queueing up, so that we don't queue things if not strictly
         * necessary:
         */
        if (!wg_birthdate_has_expired(atomic64_read(&peer->last_sent_handshake),
                                      REKEY_TIMEOUT) ||
                        unlikely(READ_ONCE(peer->is_dead)))
                goto out;

        wg_peer_get(peer);
        /* Queues up calling packet_send_queued_handshakes(peer), where we do a
         * peer_put(peer) after:
         */
        if (!queue_work(peer->device->handshake_send_wq,
                        &peer->transmit_handshake_work))
                /* If the work was already queued, we want to drop the
                 * extra reference:
                 */
                wg_peer_put(peer);
out:
        rcu_read_unlock_bh();
}

void wg_packet_send_handshake_response(struct wg_peer *peer)
{
        struct message_handshake_response packet;

        atomic64_set(&peer->last_sent_handshake, ktime_get_coarse_boottime_ns());
        net_dbg_ratelimited("%s: Sending handshake response to peer %llu (%pISpfsc)\n",
                            peer->device->dev->name, peer->internal_id,
                            &peer->endpoint.addr);

        if (wg_noise_handshake_create_response(&packet, &peer->handshake)) {
                wg_cookie_add_mac_to_packet(&packet, sizeof(packet), peer);
                if (wg_noise_handshake_begin_session(&peer->handshake,
                                                     &peer->keypairs)) {
                        wg_timers_session_derived(peer);
                        wg_timers_any_authenticated_packet_traversal(peer);
                        wg_timers_any_authenticated_packet_sent(peer);
                        atomic64_set(&peer->last_sent_handshake,
                                     ktime_get_coarse_boottime_ns());
                        wg_socket_send_buffer_to_peer(peer, &packet,
                                                      sizeof(packet),
                                                      HANDSHAKE_DSCP);
                }
        }
}

void wg_packet_send_handshake_cookie(struct wg_device *wg,
                                     struct sk_buff *initiating_skb,
                                     __le32 sender_index)
{
        struct message_handshake_cookie packet;

        net_dbg_skb_ratelimited("%s: Sending cookie response for denied handshake message for %pISpfsc\n",
                                wg->dev->name, initiating_skb);
        wg_cookie_message_create(&packet, initiating_skb, sender_index,
                                 &wg->cookie_checker);
        wg_socket_send_buffer_as_reply_to_skb(wg, initiating_skb, &packet,
                                              sizeof(packet));
}

static void keep_key_fresh(struct wg_peer *peer)
{
        struct noise_keypair *keypair;
        bool send;

        rcu_read_lock_bh();
        keypair = rcu_dereference_bh(peer->keypairs.current_keypair);
        send = keypair && READ_ONCE(keypair->sending.is_valid) &&
               (atomic64_read(&keypair->sending_counter) > REKEY_AFTER_MESSAGES ||
                (keypair->i_am_the_initiator &&
                 wg_birthdate_has_expired(keypair->sending.birthdate, REKEY_AFTER_TIME)));
        rcu_read_unlock_bh();

        if (unlikely(send))
                wg_packet_send_queued_handshake_initiation(peer, false);
}

static unsigned int calculate_skb_padding(struct sk_buff *skb)
{
        unsigned int padded_size, last_unit = skb->len;

        if (unlikely(!PACKET_CB(skb)->mtu))
                return ALIGN(last_unit, MESSAGE_PADDING_MULTIPLE) - last_unit;

        /* We do this modulo business with the MTU, just in case the networking
         * layer gives us a packet that's bigger than the MTU. In that case, we
         * wouldn't want the final subtraction to overflow in the case of the
         * padded_size being clamped. Fortunately, that's very rarely the case,
         * so we optimize for that not happening.
         */
        if (unlikely(last_unit > PACKET_CB(skb)->mtu))
                last_unit %= PACKET_CB(skb)->mtu;

        padded_size = min(PACKET_CB(skb)->mtu,
                          ALIGN(last_unit, MESSAGE_PADDING_MULTIPLE));
        return padded_size - last_unit;
}

static bool encrypt_packet(struct sk_buff *skb, struct noise_keypair *keypair)
{
        unsigned int padding_len, plaintext_len, trailer_len;
        struct scatterlist sg[MAX_SKB_FRAGS + 8];
        struct message_data *header;
        struct sk_buff *trailer;
        int num_frags;

        /* Force hash calculation before encryption so that flow analysis is
         * consistent over the inner packet.
         */
        skb_get_hash(skb);

        /* Calculate lengths. */
        padding_len = calculate_skb_padding(skb);
        trailer_len = padding_len + noise_encrypted_len(0);
        plaintext_len = skb->len + padding_len;

        /* Expand data section to have room for padding and auth tag. */
        num_frags = skb_cow_data(skb, trailer_len, &trailer);
        if (unlikely(num_frags < 0 || num_frags > ARRAY_SIZE(sg)))
                return false;

        /* Set the padding to zeros, and make sure it and the auth tag are part
         * of the skb.
         */
        memset(skb_tail_pointer(trailer), 0, padding_len);

        /* Expand head section to have room for our header and the network
         * stack's headers.
         */
        if (unlikely(skb_cow_head(skb, DATA_PACKET_HEAD_ROOM) < 0))
                return false;

        /* Finalize checksum calculation for the inner packet, if required. */
        if (unlikely(skb->ip_summed == CHECKSUM_PARTIAL &&
                     skb_checksum_help(skb)))
                return false;

        /* Only after checksumming can we safely add on the padding at the end
         * and the header.
         */
        skb_set_inner_network_header(skb, 0);
        header = (struct message_data *)skb_push(skb, sizeof(*header));
        header->header.type = cpu_to_le32(MESSAGE_DATA);
        header->key_idx = keypair->remote_index;
        header->counter = cpu_to_le64(PACKET_CB(skb)->nonce);
        pskb_put(skb, trailer, trailer_len);

        /* Now we can encrypt the scattergather segments */
        sg_init_table(sg, num_frags);
        if (skb_to_sgvec(skb, sg, sizeof(struct message_data),
                         noise_encrypted_len(plaintext_len)) <= 0)
                return false;
        return chacha20poly1305_encrypt_sg_inplace(sg, plaintext_len, NULL, 0,
                                                   PACKET_CB(skb)->nonce,
                                                   keypair->sending.key);
}

void wg_packet_send_keepalive(struct wg_peer *peer)
{
        struct sk_buff *skb;

        if (skb_queue_empty_lockless(&peer->staged_packet_queue)) {
                skb = alloc_skb(DATA_PACKET_HEAD_ROOM + MESSAGE_MINIMUM_LENGTH,
                                GFP_ATOMIC);
                if (unlikely(!skb))
                        return;
                skb_reserve(skb, DATA_PACKET_HEAD_ROOM);
                skb->dev = peer->device->dev;
                PACKET_CB(skb)->mtu = skb->dev->mtu;
                skb_queue_tail(&peer->staged_packet_queue, skb);
                net_dbg_ratelimited("%s: Sending keepalive packet to peer %llu (%pISpfsc)\n",
                                    peer->device->dev->name, peer->internal_id,
                                    &peer->endpoint.addr);
        }

        wg_packet_send_staged_packets(peer);
}

static void wg_packet_create_data_done(struct wg_peer *peer, struct sk_buff *first)
{
        struct sk_buff *skb, *next;
        bool is_keepalive, data_sent = false;

        wg_timers_any_authenticated_packet_traversal(peer);
        wg_timers_any_authenticated_packet_sent(peer);
        skb_list_walk_safe(first, skb, next) {
                is_keepalive = skb->len == message_data_len(0);
                if (likely(!wg_socket_send_skb_to_peer(peer, skb,
                                PACKET_CB(skb)->ds) && !is_keepalive))
                        data_sent = true;
        }

        if (likely(data_sent))
                wg_timers_data_sent(peer);

        keep_key_fresh(peer);
}

void wg_packet_tx_worker(struct work_struct *work)
{
        struct wg_peer *peer = container_of(work, struct wg_peer, transmit_packet_work);
        struct noise_keypair *keypair;
        enum packet_state state;
        struct sk_buff *first;

        while ((first = wg_prev_queue_peek(&peer->tx_queue)) != NULL &&
               (state = atomic_read_acquire(&PACKET_CB(first)->state)) !=
                       PACKET_STATE_UNCRYPTED) {
                wg_prev_queue_drop_peeked(&peer->tx_queue);
                keypair = PACKET_CB(first)->keypair;

                if (likely(state == PACKET_STATE_CRYPTED))
                        wg_packet_create_data_done(peer, first);
                else
                        kfree_skb_list(first);

                wg_noise_keypair_put(keypair, false);
                wg_peer_put(peer);
                if (need_resched())
                        cond_resched();
        }
}

void wg_packet_encrypt_worker(struct work_struct *work)
{
        struct crypt_queue *queue = container_of(work, struct multicore_worker,
                                                 work)->ptr;
        struct sk_buff *first, *skb, *next;

        while ((first = ptr_ring_consume_bh(&queue->ring)) != NULL) {
                enum packet_state state = PACKET_STATE_CRYPTED;

                skb_list_walk_safe(first, skb, next) {
                        if (likely(encrypt_packet(skb,
                                        PACKET_CB(first)->keypair))) {
                                wg_reset_packet(skb, true);
                        } else {
                                state = PACKET_STATE_DEAD;
                                break;
                        }
                }
                wg_queue_enqueue_per_peer_tx(first, state);
                if (need_resched())
                        cond_resched();
        }
}

static void wg_packet_create_data(struct wg_peer *peer, struct sk_buff *first)
{
        struct wg_device *wg = peer->device;
        int ret = -EINVAL;

        rcu_read_lock_bh();
        if (unlikely(READ_ONCE(peer->is_dead)))
                goto err;

        ret = wg_queue_enqueue_per_device_and_peer(&wg->encrypt_queue, &peer->tx_queue, first,
                                                   wg->packet_crypt_wq);
        if (unlikely(ret == -EPIPE))
                wg_queue_enqueue_per_peer_tx(first, PACKET_STATE_DEAD);
err:
        rcu_read_unlock_bh();
        if (likely(!ret || ret == -EPIPE))
                return;
        wg_noise_keypair_put(PACKET_CB(first)->keypair, false);
        wg_peer_put(peer);
        kfree_skb_list(first);
}

void wg_packet_purge_staged_packets(struct wg_peer *peer)
{
        spin_lock_bh(&peer->staged_packet_queue.lock);
        DEV_STATS_ADD(peer->device->dev, tx_dropped,
                      peer->staged_packet_queue.qlen);
        __skb_queue_purge(&peer->staged_packet_queue);
        spin_unlock_bh(&peer->staged_packet_queue.lock);
}

void wg_packet_send_staged_packets(struct wg_peer *peer)
{
        struct noise_keypair *keypair;
        struct sk_buff_head packets;
        struct sk_buff *skb;

        /* Steal the current queue into our local one. */
        __skb_queue_head_init(&packets);
        spin_lock_bh(&peer->staged_packet_queue.lock);
        skb_queue_splice_init(&peer->staged_packet_queue, &packets);
        spin_unlock_bh(&peer->staged_packet_queue.lock);
        if (unlikely(skb_queue_empty(&packets)))
                return;

        /* First we make sure we have a valid reference to a valid key. */
        rcu_read_lock_bh();
        keypair = wg_noise_keypair_get(
                rcu_dereference_bh(peer->keypairs.current_keypair));
        rcu_read_unlock_bh();
        if (unlikely(!keypair))
                goto out_nokey;
        if (unlikely(!READ_ONCE(keypair->sending.is_valid)))
                goto out_nokey;
        if (unlikely(wg_birthdate_has_expired(keypair->sending.birthdate,
                                              REJECT_AFTER_TIME)))
                goto out_invalid;

        /* After we know we have a somewhat valid key, we now try to assign
         * nonces to all of the packets in the queue. If we can't assign nonces
         * for all of them, we just consider it a failure and wait for the next
         * handshake.
         */
        skb_queue_walk(&packets, skb) {
                /* 0 for no outer TOS: no leak. TODO: at some later point, we
                 * might consider using flowi->tos as outer instead.
                 */
                PACKET_CB(skb)->ds = ip_tunnel_ecn_encap(0, ip_hdr(skb), skb);
                PACKET_CB(skb)->nonce =
                                atomic64_inc_return(&keypair->sending_counter) - 1;
                if (unlikely(PACKET_CB(skb)->nonce >= REJECT_AFTER_MESSAGES))
                        goto out_invalid;
        }

        packets.prev->next = NULL;
        wg_peer_get(keypair->entry.peer);
        PACKET_CB(packets.next)->keypair = keypair;
        wg_packet_create_data(peer, packets.next);
        return;

out_invalid:
        WRITE_ONCE(keypair->sending.is_valid, false);
out_nokey:
        wg_noise_keypair_put(keypair, false);

        /* We orphan the packets if we're waiting on a handshake, so that they
         * don't block a socket's pool.
         */
        skb_queue_walk(&packets, skb)
                skb_orphan(skb);
        /* Then we put them back on the top of the queue. We're not too
         * concerned about accidentally getting things a little out of order if
         * packets are being added really fast, because this queue is for before
         * packets can even be sent and it's small anyway.
         */
        spin_lock_bh(&peer->staged_packet_queue.lock);
        skb_queue_splice(&packets, &peer->staged_packet_queue);
        spin_unlock_bh(&peer->staged_packet_queue.lock);

        /* If we're exiting because there's something wrong with the key, it
         * means we should initiate a new handshake.
         */
        wg_packet_send_queued_handshake_initiation(peer, false);
}