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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-21 16:29:59 +00:00
![Yuchung Cheng](/assets/img/avatar_default.png)
Prior to this patch, active Fast Open is paused on a specific destination IP address if the previous connections to the IP address have experienced recurring timeouts . But recent experiments by Microsoft (https://goo.gl/cykmn7) and Mozilla browsers indicate the isssue is often caused by broken middle-boxes sitting close to the client. Therefore it is much better user experience if Fast Open is disabled out-right globally to avoid experiencing further timeouts on connections toward other destinations. This patch changes the destination-IP disablement to global disablement if a connection experiencing recurring timeouts or aborts due to timeout. Repeated incidents would still exponentially increase the pause time, starting from an hour. This is extremely conservative but an unfortunate compromise to minimize bad experience due to broken middle-boxes. Reported-by: Dragana Damjanovic <ddamjanovic@mozilla.com> Reported-by: Patrick McManus <mcmanus@ducksong.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Reviewed-by: Wei Wang <weiwan@google.com> Reviewed-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
536 lines
15 KiB
C
536 lines
15 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/crypto.h>
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#include <linux/err.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/list.h>
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#include <linux/tcp.h>
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#include <linux/rcupdate.h>
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#include <linux/rculist.h>
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#include <net/inetpeer.h>
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#include <net/tcp.h>
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void tcp_fastopen_init_key_once(struct net *net)
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{
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u8 key[TCP_FASTOPEN_KEY_LENGTH];
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struct tcp_fastopen_context *ctxt;
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rcu_read_lock();
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ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
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if (ctxt) {
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rcu_read_unlock();
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return;
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}
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rcu_read_unlock();
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/* tcp_fastopen_reset_cipher publishes the new context
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* atomically, so we allow this race happening here.
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*
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* All call sites of tcp_fastopen_cookie_gen also check
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* for a valid cookie, so this is an acceptable risk.
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*/
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get_random_bytes(key, sizeof(key));
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tcp_fastopen_reset_cipher(net, NULL, key, sizeof(key));
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}
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static void tcp_fastopen_ctx_free(struct rcu_head *head)
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{
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struct tcp_fastopen_context *ctx =
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container_of(head, struct tcp_fastopen_context, rcu);
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crypto_free_cipher(ctx->tfm);
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kfree(ctx);
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}
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void tcp_fastopen_destroy_cipher(struct sock *sk)
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{
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struct tcp_fastopen_context *ctx;
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ctx = rcu_dereference_protected(
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inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
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if (ctx)
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call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
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}
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void tcp_fastopen_ctx_destroy(struct net *net)
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{
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struct tcp_fastopen_context *ctxt;
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spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
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ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
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lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
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rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
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spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
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if (ctxt)
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call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
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}
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int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
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void *key, unsigned int len)
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{
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struct tcp_fastopen_context *ctx, *octx;
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struct fastopen_queue *q;
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int err;
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return -ENOMEM;
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ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
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if (IS_ERR(ctx->tfm)) {
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err = PTR_ERR(ctx->tfm);
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error: kfree(ctx);
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pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
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return err;
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}
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err = crypto_cipher_setkey(ctx->tfm, key, len);
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if (err) {
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pr_err("TCP: TFO cipher key error: %d\n", err);
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crypto_free_cipher(ctx->tfm);
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goto error;
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}
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memcpy(ctx->key, key, len);
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spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
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if (sk) {
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q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
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octx = rcu_dereference_protected(q->ctx,
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lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
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rcu_assign_pointer(q->ctx, ctx);
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} else {
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octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
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lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
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rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
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}
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spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
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if (octx)
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call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
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return err;
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}
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static bool __tcp_fastopen_cookie_gen(struct sock *sk, const void *path,
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struct tcp_fastopen_cookie *foc)
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{
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struct tcp_fastopen_context *ctx;
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bool ok = false;
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rcu_read_lock();
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ctx = rcu_dereference(inet_csk(sk)->icsk_accept_queue.fastopenq.ctx);
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if (!ctx)
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ctx = rcu_dereference(sock_net(sk)->ipv4.tcp_fastopen_ctx);
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if (ctx) {
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crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
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foc->len = TCP_FASTOPEN_COOKIE_SIZE;
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ok = true;
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}
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rcu_read_unlock();
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return ok;
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}
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/* Generate the fastopen cookie by doing aes128 encryption on both
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* the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
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* addresses. For the longer IPv6 addresses use CBC-MAC.
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*
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* XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
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*/
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static bool tcp_fastopen_cookie_gen(struct sock *sk,
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struct request_sock *req,
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struct sk_buff *syn,
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struct tcp_fastopen_cookie *foc)
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{
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if (req->rsk_ops->family == AF_INET) {
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const struct iphdr *iph = ip_hdr(syn);
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__be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
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return __tcp_fastopen_cookie_gen(sk, path, foc);
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}
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#if IS_ENABLED(CONFIG_IPV6)
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if (req->rsk_ops->family == AF_INET6) {
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const struct ipv6hdr *ip6h = ipv6_hdr(syn);
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struct tcp_fastopen_cookie tmp;
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if (__tcp_fastopen_cookie_gen(sk, &ip6h->saddr, &tmp)) {
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struct in6_addr *buf = &tmp.addr;
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int i;
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for (i = 0; i < 4; i++)
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buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
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return __tcp_fastopen_cookie_gen(sk, buf, foc);
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}
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}
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#endif
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return false;
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}
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/* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
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* queue this additional data / FIN.
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*/
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void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
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return;
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skb = skb_clone(skb, GFP_ATOMIC);
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if (!skb)
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return;
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skb_dst_drop(skb);
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/* segs_in has been initialized to 1 in tcp_create_openreq_child().
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* Hence, reset segs_in to 0 before calling tcp_segs_in()
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* to avoid double counting. Also, tcp_segs_in() expects
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* skb->len to include the tcp_hdrlen. Hence, it should
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* be called before __skb_pull().
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*/
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tp->segs_in = 0;
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tcp_segs_in(tp, skb);
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__skb_pull(skb, tcp_hdrlen(skb));
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sk_forced_mem_schedule(sk, skb->truesize);
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skb_set_owner_r(skb, sk);
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TCP_SKB_CB(skb)->seq++;
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TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
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tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
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__skb_queue_tail(&sk->sk_receive_queue, skb);
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tp->syn_data_acked = 1;
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/* u64_stats_update_begin(&tp->syncp) not needed here,
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* as we certainly are not changing upper 32bit value (0)
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*/
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tp->bytes_received = skb->len;
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if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
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tcp_fin(sk);
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}
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static struct sock *tcp_fastopen_create_child(struct sock *sk,
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struct sk_buff *skb,
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struct request_sock *req)
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{
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struct tcp_sock *tp;
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struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
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struct sock *child;
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bool own_req;
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req->num_retrans = 0;
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req->num_timeout = 0;
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req->sk = NULL;
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child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
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NULL, &own_req);
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if (!child)
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return NULL;
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spin_lock(&queue->fastopenq.lock);
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queue->fastopenq.qlen++;
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spin_unlock(&queue->fastopenq.lock);
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/* Initialize the child socket. Have to fix some values to take
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* into account the child is a Fast Open socket and is created
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* only out of the bits carried in the SYN packet.
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*/
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tp = tcp_sk(child);
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tp->fastopen_rsk = req;
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tcp_rsk(req)->tfo_listener = true;
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/* RFC1323: The window in SYN & SYN/ACK segments is never
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* scaled. So correct it appropriately.
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*/
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tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
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tp->max_window = tp->snd_wnd;
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/* Activate the retrans timer so that SYNACK can be retransmitted.
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* The request socket is not added to the ehash
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* because it's been added to the accept queue directly.
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*/
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inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
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TCP_TIMEOUT_INIT, TCP_RTO_MAX);
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refcount_set(&req->rsk_refcnt, 2);
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/* Now finish processing the fastopen child socket. */
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tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
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tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
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tcp_fastopen_add_skb(child, skb);
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tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
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tp->rcv_wup = tp->rcv_nxt;
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/* tcp_conn_request() is sending the SYNACK,
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* and queues the child into listener accept queue.
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*/
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return child;
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}
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static bool tcp_fastopen_queue_check(struct sock *sk)
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{
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struct fastopen_queue *fastopenq;
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/* Make sure the listener has enabled fastopen, and we don't
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* exceed the max # of pending TFO requests allowed before trying
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* to validating the cookie in order to avoid burning CPU cycles
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* unnecessarily.
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*
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* XXX (TFO) - The implication of checking the max_qlen before
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* processing a cookie request is that clients can't differentiate
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* between qlen overflow causing Fast Open to be disabled
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* temporarily vs a server not supporting Fast Open at all.
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*/
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fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
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if (fastopenq->max_qlen == 0)
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return false;
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if (fastopenq->qlen >= fastopenq->max_qlen) {
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struct request_sock *req1;
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spin_lock(&fastopenq->lock);
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req1 = fastopenq->rskq_rst_head;
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if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
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__NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
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spin_unlock(&fastopenq->lock);
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return false;
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}
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fastopenq->rskq_rst_head = req1->dl_next;
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fastopenq->qlen--;
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spin_unlock(&fastopenq->lock);
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reqsk_put(req1);
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}
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return true;
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}
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static bool tcp_fastopen_no_cookie(const struct sock *sk,
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const struct dst_entry *dst,
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int flag)
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{
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return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
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tcp_sk(sk)->fastopen_no_cookie ||
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(dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
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}
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/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
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* may be updated and return the client in the SYN-ACK later. E.g., Fast Open
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* cookie request (foc->len == 0).
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*/
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struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
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struct request_sock *req,
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struct tcp_fastopen_cookie *foc,
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const struct dst_entry *dst)
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{
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bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
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int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
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struct tcp_fastopen_cookie valid_foc = { .len = -1 };
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struct sock *child;
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if (foc->len == 0) /* Client requests a cookie */
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NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
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if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
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(syn_data || foc->len >= 0) &&
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tcp_fastopen_queue_check(sk))) {
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foc->len = -1;
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return NULL;
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}
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if (syn_data &&
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tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
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goto fastopen;
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if (foc->len >= 0 && /* Client presents or requests a cookie */
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tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc) &&
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foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
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foc->len == valid_foc.len &&
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!memcmp(foc->val, valid_foc.val, foc->len)) {
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/* Cookie is valid. Create a (full) child socket to accept
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* the data in SYN before returning a SYN-ACK to ack the
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* data. If we fail to create the socket, fall back and
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* ack the ISN only but includes the same cookie.
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*
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* Note: Data-less SYN with valid cookie is allowed to send
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* data in SYN_RECV state.
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*/
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fastopen:
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child = tcp_fastopen_create_child(sk, skb, req);
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if (child) {
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foc->len = -1;
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPFASTOPENPASSIVE);
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return child;
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}
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NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
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} else if (foc->len > 0) /* Client presents an invalid cookie */
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NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
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valid_foc.exp = foc->exp;
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*foc = valid_foc;
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return NULL;
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}
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bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
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struct tcp_fastopen_cookie *cookie)
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{
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const struct dst_entry *dst;
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tcp_fastopen_cache_get(sk, mss, cookie);
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/* Firewall blackhole issue check */
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if (tcp_fastopen_active_should_disable(sk)) {
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cookie->len = -1;
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return false;
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}
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dst = __sk_dst_get(sk);
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if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
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cookie->len = -1;
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return true;
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}
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return cookie->len > 0;
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}
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/* This function checks if we want to defer sending SYN until the first
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* write(). We defer under the following conditions:
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* 1. fastopen_connect sockopt is set
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* 2. we have a valid cookie
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* Return value: return true if we want to defer until application writes data
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* return false if we want to send out SYN immediately
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*/
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bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
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{
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struct tcp_fastopen_cookie cookie = { .len = 0 };
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struct tcp_sock *tp = tcp_sk(sk);
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u16 mss;
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if (tp->fastopen_connect && !tp->fastopen_req) {
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if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
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inet_sk(sk)->defer_connect = 1;
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return true;
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}
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/* Alloc fastopen_req in order for FO option to be included
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* in SYN
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*/
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tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
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sk->sk_allocation);
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if (tp->fastopen_req)
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tp->fastopen_req->cookie = cookie;
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else
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*err = -ENOBUFS;
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}
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return false;
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}
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EXPORT_SYMBOL(tcp_fastopen_defer_connect);
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/*
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* The following code block is to deal with middle box issues with TFO:
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* Middlebox firewall issues can potentially cause server's data being
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* blackholed after a successful 3WHS using TFO.
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* The proposed solution is to disable active TFO globally under the
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* following circumstances:
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* 1. client side TFO socket receives out of order FIN
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* 2. client side TFO socket receives out of order RST
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* 3. client side TFO socket has timed out three times consecutively during
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* or after handshake
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* We disable active side TFO globally for 1hr at first. Then if it
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* happens again, we disable it for 2h, then 4h, 8h, ...
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* And we reset the timeout back to 1hr when we see a successful active
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* TFO connection with data exchanges.
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*/
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/* Disable active TFO and record current jiffies and
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* tfo_active_disable_times
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*/
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void tcp_fastopen_active_disable(struct sock *sk)
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{
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struct net *net = sock_net(sk);
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atomic_inc(&net->ipv4.tfo_active_disable_times);
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net->ipv4.tfo_active_disable_stamp = jiffies;
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NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
|
|
}
|
|
|
|
/* Calculate timeout for tfo active disable
|
|
* Return true if we are still in the active TFO disable period
|
|
* Return false if timeout already expired and we should use active TFO
|
|
*/
|
|
bool tcp_fastopen_active_should_disable(struct sock *sk)
|
|
{
|
|
unsigned int tfo_bh_timeout = sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout;
|
|
int tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
|
|
unsigned long timeout;
|
|
int multiplier;
|
|
|
|
if (!tfo_da_times)
|
|
return false;
|
|
|
|
/* Limit timout to max: 2^6 * initial timeout */
|
|
multiplier = 1 << min(tfo_da_times - 1, 6);
|
|
timeout = multiplier * tfo_bh_timeout * HZ;
|
|
if (time_before(jiffies, sock_net(sk)->ipv4.tfo_active_disable_stamp + timeout))
|
|
return true;
|
|
|
|
/* Mark check bit so we can check for successful active TFO
|
|
* condition and reset tfo_active_disable_times
|
|
*/
|
|
tcp_sk(sk)->syn_fastopen_ch = 1;
|
|
return false;
|
|
}
|
|
|
|
/* Disable active TFO if FIN is the only packet in the ofo queue
|
|
* and no data is received.
|
|
* Also check if we can reset tfo_active_disable_times if data is
|
|
* received successfully on a marked active TFO sockets opened on
|
|
* a non-loopback interface
|
|
*/
|
|
void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
|
|
{
|
|
struct tcp_sock *tp = tcp_sk(sk);
|
|
struct dst_entry *dst;
|
|
struct sk_buff *skb;
|
|
|
|
if (!tp->syn_fastopen)
|
|
return;
|
|
|
|
if (!tp->data_segs_in) {
|
|
skb = skb_rb_first(&tp->out_of_order_queue);
|
|
if (skb && !skb_rb_next(skb)) {
|
|
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
|
|
tcp_fastopen_active_disable(sk);
|
|
return;
|
|
}
|
|
}
|
|
} else if (tp->syn_fastopen_ch &&
|
|
atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
|
|
dst = sk_dst_get(sk);
|
|
if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
|
|
atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
|
|
dst_release(dst);
|
|
}
|
|
}
|
|
|
|
void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
|
|
{
|
|
u32 timeouts = inet_csk(sk)->icsk_retransmits;
|
|
struct tcp_sock *tp = tcp_sk(sk);
|
|
|
|
/* Broken middle-boxes may black-hole Fast Open connection during or
|
|
* even after the handshake. Be extremely conservative and pause
|
|
* Fast Open globally after hitting the third consecutive timeout or
|
|
* exceeding the configured timeout limit.
|
|
*/
|
|
if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
|
|
(timeouts == 2 || (timeouts < 2 && expired))) {
|
|
tcp_fastopen_active_disable(sk);
|
|
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
|
|
}
|
|
}
|