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synced 2024-08-23 17:30:02 +00:00
![Luke Hsiao](/assets/img/avatar_default.png)
Since the original TFO server code was implemented in commit
168a8f5805
("tcp: TCP Fast Open Server -
main code path") the TFO server code has supported the sysctl bit flag
TFO_SERVER_COOKIE_NOT_REQD. Currently, when the TFO_SERVER_ENABLE and
TFO_SERVER_COOKIE_NOT_REQD sysctl bit flags are set, a server connection
will accept a SYN with N bytes of data (N > 0) that has no TFO cookie,
create a new fast open connection, process the incoming data in the SYN,
and make the connection ready for accepting. After accepting, the
connection is ready for read()/recvmsg() to read the N bytes of data in
the SYN, ready for write()/sendmsg() calls and data transmissions to
transmit data.
This commit changes an edge case in this feature by changing this
behavior to apply to (N >= 0) bytes of data in the SYN rather than only
(N > 0) bytes of data in the SYN. Now, a server will accept a data-less
SYN without a TFO cookie if TFO_SERVER_COOKIE_NOT_REQD is set.
Caveat! While this enables a new kind of TFO (data-less empty-cookie
SYN), some firewall rules setup may not work if they assume such packets
are not legit TFOs and will filter them.
Signed-off-by: Luke Hsiao <lukehsiao@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20210816205105.2533289-1-luke.w.hsiao@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
597 lines
17 KiB
C
597 lines
17 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, NULL);
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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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kfree_sensitive(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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ctxt = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, NULL);
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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 *primary_key, void *backup_key)
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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 = 0;
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx) {
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err = -ENOMEM;
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goto out;
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}
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ctx->key[0].key[0] = get_unaligned_le64(primary_key);
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ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
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if (backup_key) {
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ctx->key[1].key[0] = get_unaligned_le64(backup_key);
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ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
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ctx->num = 2;
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} else {
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ctx->num = 1;
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}
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if (sk) {
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q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
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octx = xchg((__force struct tcp_fastopen_context **)&q->ctx, ctx);
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} else {
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octx = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, ctx);
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}
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if (octx)
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call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
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out:
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return err;
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}
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int tcp_fastopen_get_cipher(struct net *net, struct inet_connection_sock *icsk,
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u64 *key)
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{
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struct tcp_fastopen_context *ctx;
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int n_keys = 0, i;
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rcu_read_lock();
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if (icsk)
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ctx = rcu_dereference(icsk->icsk_accept_queue.fastopenq.ctx);
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else
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ctx = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
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if (ctx) {
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n_keys = tcp_fastopen_context_len(ctx);
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for (i = 0; i < n_keys; i++) {
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put_unaligned_le64(ctx->key[i].key[0], key + (i * 2));
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put_unaligned_le64(ctx->key[i].key[1], key + (i * 2) + 1);
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}
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}
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rcu_read_unlock();
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return n_keys;
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}
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static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
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struct sk_buff *syn,
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const siphash_key_t *key,
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struct tcp_fastopen_cookie *foc)
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{
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BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
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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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foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
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sizeof(iph->saddr) +
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sizeof(iph->daddr),
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key));
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foc->len = TCP_FASTOPEN_COOKIE_SIZE;
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return true;
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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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foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
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sizeof(ip6h->saddr) +
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sizeof(ip6h->daddr),
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key));
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foc->len = TCP_FASTOPEN_COOKIE_SIZE;
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return true;
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}
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#endif
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return false;
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}
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/* Generate the fastopen cookie by applying SipHash to both the source and
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* destination addresses.
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*/
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static void 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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struct tcp_fastopen_context *ctx;
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rcu_read_lock();
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ctx = tcp_fastopen_get_ctx(sk);
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if (ctx)
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__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
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rcu_read_unlock();
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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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/* returns 0 - no key match, 1 for primary, 2 for backup */
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static int tcp_fastopen_cookie_gen_check(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 *orig,
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struct tcp_fastopen_cookie *valid_foc)
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{
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struct tcp_fastopen_cookie search_foc = { .len = -1 };
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struct tcp_fastopen_cookie *foc = valid_foc;
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struct tcp_fastopen_context *ctx;
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int i, ret = 0;
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rcu_read_lock();
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ctx = tcp_fastopen_get_ctx(sk);
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if (!ctx)
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goto out;
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for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
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__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
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if (tcp_fastopen_cookie_match(foc, orig)) {
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ret = i + 1;
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goto out;
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}
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foc = &search_foc;
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}
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out:
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rcu_read_unlock();
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return ret;
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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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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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rcu_assign_pointer(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, skb);
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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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int ret = 0;
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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 (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) {
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/* Client requests a cookie. */
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tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc);
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} else if (foc->len > 0) {
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ret = tcp_fastopen_cookie_gen_check(sk, req, skb, foc,
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&valid_foc);
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if (!ret) {
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
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} else {
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/* Cookie is valid. Create a (full) child socket to
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* accept the data in SYN before returning a SYN-ACK to
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* ack the data. If we fail to create the socket, fall
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* back and ack the ISN only but includes the same
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* cookie.
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*
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* Note: Data-less SYN with valid cookie is allowed to
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* send 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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if (ret == 2) {
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valid_foc.exp = foc->exp;
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*foc = valid_foc;
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NET_INC_STATS(sock_net(sk),
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LINUX_MIB_TCPFASTOPENPASSIVEALTKEY);
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} else {
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foc->len = -1;
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}
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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),
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LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
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}
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}
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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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if (cookie->len > 0)
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return true;
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tcp_sk(sk)->fastopen_client_fail = TFO_COOKIE_UNAVAILABLE;
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return false;
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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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|
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if (tp->fastopen_connect && !tp->fastopen_req) {
|
|
if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
|
|
inet_sk(sk)->defer_connect = 1;
|
|
return true;
|
|
}
|
|
|
|
/* Alloc fastopen_req in order for FO option to be included
|
|
* in SYN
|
|
*/
|
|
tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
|
|
sk->sk_allocation);
|
|
if (tp->fastopen_req)
|
|
tp->fastopen_req->cookie = cookie;
|
|
else
|
|
*err = -ENOBUFS;
|
|
}
|
|
return false;
|
|
}
|
|
EXPORT_SYMBOL(tcp_fastopen_defer_connect);
|
|
|
|
/*
|
|
* The following code block is to deal with middle box issues with TFO:
|
|
* Middlebox firewall issues can potentially cause server's data being
|
|
* blackholed after a successful 3WHS using TFO.
|
|
* The proposed solution is to disable active TFO globally under the
|
|
* following circumstances:
|
|
* 1. client side TFO socket receives out of order FIN
|
|
* 2. client side TFO socket receives out of order RST
|
|
* 3. client side TFO socket has timed out three times consecutively during
|
|
* or after handshake
|
|
* We disable active side TFO globally for 1hr at first. Then if it
|
|
* happens again, we disable it for 2h, then 4h, 8h, ...
|
|
* And we reset the timeout back to 1hr when we see a successful active
|
|
* TFO connection with data exchanges.
|
|
*/
|
|
|
|
/* Disable active TFO and record current jiffies and
|
|
* tfo_active_disable_times
|
|
*/
|
|
void tcp_fastopen_active_disable(struct sock *sk)
|
|
{
|
|
struct net *net = sock_net(sk);
|
|
|
|
if (!sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout)
|
|
return;
|
|
|
|
/* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
|
|
WRITE_ONCE(net->ipv4.tfo_active_disable_stamp, jiffies);
|
|
|
|
/* Paired with smp_rmb() in tcp_fastopen_active_should_disable().
|
|
* We want net->ipv4.tfo_active_disable_stamp to be updated first.
|
|
*/
|
|
smp_mb__before_atomic();
|
|
atomic_inc(&net->ipv4.tfo_active_disable_times);
|
|
|
|
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;
|
|
unsigned long timeout;
|
|
int tfo_da_times;
|
|
int multiplier;
|
|
|
|
if (!tfo_bh_timeout)
|
|
return false;
|
|
|
|
tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
|
|
if (!tfo_da_times)
|
|
return false;
|
|
|
|
/* Paired with smp_mb__before_atomic() in tcp_fastopen_active_disable() */
|
|
smp_rmb();
|
|
|
|
/* Limit timeout to max: 2^6 * initial timeout */
|
|
multiplier = 1 << min(tfo_da_times - 1, 6);
|
|
|
|
/* Paired with the WRITE_ONCE() in tcp_fastopen_active_disable(). */
|
|
timeout = READ_ONCE(sock_net(sk)->ipv4.tfo_active_disable_stamp) +
|
|
multiplier * tfo_bh_timeout * HZ;
|
|
if (time_before(jiffies, 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);
|
|
}
|
|
}
|