#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/tcp.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <net/inetpeer.h>
#include <net/tcp.h>

int sysctl_tcp_fastopen __read_mostly = TFO_CLIENT_ENABLE;

struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;

static DEFINE_SPINLOCK(tcp_fastopen_ctx_lock);

void tcp_fastopen_init_key_once(bool publish)
{
        static u8 key[TCP_FASTOPEN_KEY_LENGTH];

        /* tcp_fastopen_reset_cipher publishes the new context
         * atomically, so we allow this race happening here.
         *
         * All call sites of tcp_fastopen_cookie_gen also check
         * for a valid cookie, so this is an acceptable risk.
         */
        if (net_get_random_once(key, sizeof(key)) && publish)
                tcp_fastopen_reset_cipher(key, sizeof(key));
}

static void tcp_fastopen_ctx_free(struct rcu_head *head)
{
        struct tcp_fastopen_context *ctx =
            container_of(head, struct tcp_fastopen_context, rcu);
        crypto_free_cipher(ctx->tfm);
        kfree(ctx);
}

int tcp_fastopen_reset_cipher(void *key, unsigned int len)
{
        int err;
        struct tcp_fastopen_context *ctx, *octx;

        ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;
        ctx->tfm = crypto_alloc_cipher("aes", 0, 0);

        if (IS_ERR(ctx->tfm)) {
                err = PTR_ERR(ctx->tfm);
error:          kfree(ctx);
                pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
                return err;
        }
        err = crypto_cipher_setkey(ctx->tfm, key, len);
        if (err) {
                pr_err("TCP: TFO cipher key error: %d\n", err);
                crypto_free_cipher(ctx->tfm);
                goto error;
        }
        memcpy(ctx->key, key, len);

        spin_lock(&tcp_fastopen_ctx_lock);

        octx = rcu_dereference_protected(tcp_fastopen_ctx,
                                lockdep_is_held(&tcp_fastopen_ctx_lock));
        rcu_assign_pointer(tcp_fastopen_ctx, ctx);
        spin_unlock(&tcp_fastopen_ctx_lock);

        if (octx)
                call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
        return err;
}

static bool __tcp_fastopen_cookie_gen(const void *path,
                                      struct tcp_fastopen_cookie *foc)
{
        struct tcp_fastopen_context *ctx;
        bool ok = false;

        tcp_fastopen_init_key_once(true);

        rcu_read_lock();
        ctx = rcu_dereference(tcp_fastopen_ctx);
        if (ctx) {
                crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
                foc->len = TCP_FASTOPEN_COOKIE_SIZE;
                ok = true;
        }
        rcu_read_unlock();
        return ok;
}

/* Generate the fastopen cookie by doing aes128 encryption on both
 * the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
 * addresses. For the longer IPv6 addresses use CBC-MAC.
 *
 * XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
 */
static bool tcp_fastopen_cookie_gen(struct request_sock *req,
                                    struct sk_buff *syn,
                                    struct tcp_fastopen_cookie *foc)
{
        if (req->rsk_ops->family == AF_INET) {
                const struct iphdr *iph = ip_hdr(syn);

                __be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
                return __tcp_fastopen_cookie_gen(path, foc);
        }

#if IS_ENABLED(CONFIG_IPV6)
        if (req->rsk_ops->family == AF_INET6) {
                const struct ipv6hdr *ip6h = ipv6_hdr(syn);
                struct tcp_fastopen_cookie tmp;

                if (__tcp_fastopen_cookie_gen(&ip6h->saddr, &tmp)) {
                        struct in6_addr *buf = (struct in6_addr *) tmp.val;
                        int i;

                        for (i = 0; i < 4; i++)
                                buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
                        return __tcp_fastopen_cookie_gen(buf, foc);
                }
        }
#endif
        return false;
}

static bool tcp_fastopen_create_child(struct sock *sk,
                                      struct sk_buff *skb,
                                      struct dst_entry *dst,
                                      struct request_sock *req)
{
        struct tcp_sock *tp;
        struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
        struct sock *child;

        req->num_retrans = 0;
        req->num_timeout = 0;
        req->sk = NULL;

        child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
        if (child == NULL)
                return false;

        spin_lock(&queue->fastopenq->lock);
        queue->fastopenq->qlen++;
        spin_unlock(&queue->fastopenq->lock);

        /* Initialize the child socket. Have to fix some values to take
         * into account the child is a Fast Open socket and is created
         * only out of the bits carried in the SYN packet.
         */
        tp = tcp_sk(child);

        tp->fastopen_rsk = req;
        /* Do a hold on the listner sk so that if the listener is being
         * closed, the child that has been accepted can live on and still
         * access listen_lock.
         */
        sock_hold(sk);
        tcp_rsk(req)->listener = sk;

        /* RFC1323: The window in SYN & SYN/ACK segments is never
         * scaled. So correct it appropriately.
         */
        tp->snd_wnd = ntohs(tcp_hdr(skb)->window);

        /* Activate the retrans timer so that SYNACK can be retransmitted.
         * The request socket is not added to the SYN table of the parent
         * because it's been added to the accept queue directly.
         */
        inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
                                  TCP_TIMEOUT_INIT, TCP_RTO_MAX);

        /* Add the child socket directly into the accept queue */
        inet_csk_reqsk_queue_add(sk, req, child);

        /* Now finish processing the fastopen child socket. */
        inet_csk(child)->icsk_af_ops->rebuild_header(child);
        tcp_init_congestion_control(child);
        tcp_mtup_init(child);
        tcp_init_metrics(child);
        tcp_init_buffer_space(child);

        /* Queue the data carried in the SYN packet. We need to first
         * bump skb's refcnt because the caller will attempt to free it.
         *
         * XXX (TFO) - we honor a zero-payload TFO request for now,
         * (any reason not to?) but no need to queue the skb since
         * there is no data. How about SYN+FIN?
         */
        if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1) {
                skb = skb_get(skb);
                skb_dst_drop(skb);
                __skb_pull(skb, tcp_hdr(skb)->doff * 4);
                skb_set_owner_r(skb, child);
                __skb_queue_tail(&child->sk_receive_queue, skb);
                tp->syn_data_acked = 1;
        }
        tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
        sk->sk_data_ready(sk);
        bh_unlock_sock(child);
        sock_put(child);
        WARN_ON(req->sk == NULL);
        return true;
}
EXPORT_SYMBOL(tcp_fastopen_create_child);

static bool tcp_fastopen_queue_check(struct sock *sk)
{
        struct fastopen_queue *fastopenq;

        /* Make sure the listener has enabled fastopen, and we don't
         * exceed the max # of pending TFO requests allowed before trying
         * to validating the cookie in order to avoid burning CPU cycles
         * unnecessarily.
         *
         * XXX (TFO) - The implication of checking the max_qlen before
         * processing a cookie request is that clients can't differentiate
         * between qlen overflow causing Fast Open to be disabled
         * temporarily vs a server not supporting Fast Open at all.
         */
        fastopenq = inet_csk(sk)->icsk_accept_queue.fastopenq;
        if (fastopenq == NULL || fastopenq->max_qlen == 0)
                return false;

        if (fastopenq->qlen >= fastopenq->max_qlen) {
                struct request_sock *req1;
                spin_lock(&fastopenq->lock);
                req1 = fastopenq->rskq_rst_head;
                if ((req1 == NULL) || time_after(req1->expires, jiffies)) {
                        spin_unlock(&fastopenq->lock);
                        NET_INC_STATS_BH(sock_net(sk),
                                         LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
                        return false;
                }
                fastopenq->rskq_rst_head = req1->dl_next;
                fastopenq->qlen--;
                spin_unlock(&fastopenq->lock);
                reqsk_free(req1);
        }
        return true;
}

/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
 * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
 * cookie request (foc->len == 0).
 */
bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
                      struct request_sock *req,
                      struct tcp_fastopen_cookie *foc,
                      struct dst_entry *dst)
{
        struct tcp_fastopen_cookie valid_foc = { .len = -1 };
        bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;

        if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
              (syn_data || foc->len >= 0) &&
              tcp_fastopen_queue_check(sk))) {
                foc->len = -1;
                return false;
        }

        if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
                goto fastopen;

        if (tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&
            foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
            foc->len == valid_foc.len &&
            !memcmp(foc->val, valid_foc.val, foc->len)) {
                /* Cookie is valid. Create a (full) child socket to accept
                 * the data in SYN before returning a SYN-ACK to ack the
                 * data. If we fail to create the socket, fall back and
                 * ack the ISN only but includes the same cookie.
                 *
                 * Note: Data-less SYN with valid cookie is allowed to send
                 * data in SYN_RECV state.
                 */
fastopen:
                if (tcp_fastopen_create_child(sk, skb, dst, req)) {
                        foc->len = -1;
                        NET_INC_STATS_BH(sock_net(sk),
                                         LINUX_MIB_TCPFASTOPENPASSIVE);
                        return true;
                }
        }

        NET_INC_STATS_BH(sock_net(sk), foc->len ?
                         LINUX_MIB_TCPFASTOPENPASSIVEFAIL :
                         LINUX_MIB_TCPFASTOPENCOOKIEREQD);
        *foc = valid_foc;
        return false;
}
EXPORT_SYMBOL(tcp_try_fastopen);