1 files changed, 148 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b5c23756965a..97e48d60c4e8 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5877,3 +5877,151 @@ discard:
         return 0;
 }
 EXPORT_SYMBOL(tcp_rcv_state_process);
+
+static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
+{
+        struct inet_request_sock *ireq = inet_rsk(req);
+
+        if (family == AF_INET)
+                LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("drop open request from %pI4/%u\n"),
+                               &ireq->ir_rmt_addr, port);
+        else
+                LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("drop open request from %pI6/%u\n"),
+                               &ireq->ir_v6_rmt_addr, port);
+}
+
+int tcp_conn_request(struct request_sock_ops *rsk_ops,
+                     const struct tcp_request_sock_ops *af_ops,
+                     struct sock *sk, struct sk_buff *skb)
+{
+        struct tcp_options_received tmp_opt;
+        struct request_sock *req;
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct dst_entry *dst = NULL;
+        __u32 isn = TCP_SKB_CB(skb)->when;
+        bool want_cookie = false, fastopen;
+        struct flowi fl;
+        struct tcp_fastopen_cookie foc = { .len = -1 };
+        int err;
+
+
+        /* TW buckets are converted to open requests without
+         * limitations, they conserve resources and peer is
+         * evidently real one.
+         */
+        if ((sysctl_tcp_syncookies == 2 ||
+             inet_csk_reqsk_queue_is_full(sk)) && !isn) {
+                want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
+                if (!want_cookie)
+                        goto drop;
+        }
+
+
+        /* Accept backlog is full. If we have already queued enough
+         * of warm entries in syn queue, drop request. It is better than
+         * clogging syn queue with openreqs with exponentially increasing
+         * timeout.
+         */
+        if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
+                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+                goto drop;
+        }
+
+        req = inet_reqsk_alloc(rsk_ops);
+        if (!req)
+                goto drop;
+
+        tcp_rsk(req)->af_specific = af_ops;
+
+        tcp_clear_options(&tmp_opt);
+        tmp_opt.mss_clamp = af_ops->mss_clamp;
+        tmp_opt.user_mss  = tp->rx_opt.user_mss;
+        tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
+
+        if (want_cookie && !tmp_opt.saw_tstamp)
+                tcp_clear_options(&tmp_opt);
+
+        tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
+        tcp_openreq_init(req, &tmp_opt, skb, sk);
+
+        af_ops->init_req(req, sk, skb);
+
+        if (security_inet_conn_request(sk, skb, req))
+                goto drop_and_free;
+
+        if (!want_cookie || tmp_opt.tstamp_ok)
+                TCP_ECN_create_request(req, skb, sock_net(sk));
+
+        if (want_cookie) {
+                isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
+                req->cookie_ts = tmp_opt.tstamp_ok;
+        } else if (!isn) {
+                /* VJ's idea. We save last timestamp seen
+                 * from the destination in peer table, when entering
+                 * state TIME-WAIT, and check against it before
+                 * accepting new connection request.
+                 *
+                 * If "isn" is not zero, this request hit alive
+                 * timewait bucket, so that all the necessary checks
+                 * are made in the function processing timewait state.
+                 */
+                if (tmp_opt.saw_tstamp && tcp_death_row.sysctl_tw_recycle) {
+                        bool strict;
+
+                        dst = af_ops->route_req(sk, &fl, req, &strict);
+                        if (dst && strict &&
+                            !tcp_peer_is_proven(req, dst, true)) {
+                                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
+                                goto drop_and_release;
+                        }
+                }
+                /* Kill the following clause, if you dislike this way. */
+                else if (!sysctl_tcp_syncookies &&
+                         (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
+                          (sysctl_max_syn_backlog >> 2)) &&
+                         !tcp_peer_is_proven(req, dst, false)) {
+                        /* Without syncookies last quarter of
+                         * backlog is filled with destinations,
+                         * proven to be alive.
+                         * It means that we continue to communicate
+                         * to destinations, already remembered
+                         * to the moment of synflood.
+                         */
+                        pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
+                                    rsk_ops->family);
+                        goto drop_and_release;
+                }
+
+                isn = af_ops->init_seq(skb);
+        }
+        if (!dst) {
+                dst = af_ops->route_req(sk, &fl, req, NULL);
+                if (!dst)
+                        goto drop_and_free;
+        }
+
+        tcp_rsk(req)->snt_isn = isn;
+        tcp_openreq_init_rwin(req, sk, dst);
+        fastopen = !want_cookie &&
+                   tcp_try_fastopen(sk, skb, req, &foc, dst);
+        err = af_ops->send_synack(sk, dst, &fl, req,
+                                  skb_get_queue_mapping(skb), &foc);
+        if (!fastopen) {
+                if (err || want_cookie)
+                        goto drop_and_free;
+
+                tcp_rsk(req)->listener = NULL;
+                af_ops->queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+        }
+
+        return 0;
+
+drop_and_release:
+        dst_release(dst);
+drop_and_free:
+        reqsk_free(req);
+drop:
+        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
+        return 0;
+}
+EXPORT_SYMBOL(tcp_conn_request);