linux/net/ipv4/tcp_fastopen.c

533 lines
15 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/crypto.h>
#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>
void tcp_fastopen_init_key_once(struct net *net)
{
u8 key[TCP_FASTOPEN_KEY_LENGTH];
struct tcp_fastopen_context *ctxt;
rcu_read_lock();
ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
if (ctxt) {
rcu_read_unlock();
return;
}
rcu_read_unlock();
/* 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.
*/
get_random_bytes(key, sizeof(key));
tcp_fastopen_reset_cipher(net, NULL, 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);
}
void tcp_fastopen_destroy_cipher(struct sock *sk)
{
struct tcp_fastopen_context *ctx;
ctx = rcu_dereference_protected(
inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
if (ctx)
call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
}
void tcp_fastopen_ctx_destroy(struct net *net)
{
struct tcp_fastopen_context *ctxt;
spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
if (ctxt)
call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
}
int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
void *key, unsigned int len)
{
struct tcp_fastopen_context *ctx, *octx;
struct fastopen_queue *q;
int err;
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(&net->ipv4.tcp_fastopen_ctx_lock);
if (sk) {
q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
octx = rcu_dereference_protected(q->ctx,
lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
rcu_assign_pointer(q->ctx, ctx);
} else {
octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
}
spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
if (octx)
call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
return err;
}
static bool __tcp_fastopen_cookie_gen(struct sock *sk, const void *path,
struct tcp_fastopen_cookie *foc)
{
struct tcp_fastopen_context *ctx;
bool ok = false;
rcu_read_lock();
ctx = rcu_dereference(inet_csk(sk)->icsk_accept_queue.fastopenq.ctx);
if (!ctx)
ctx = rcu_dereference(sock_net(sk)->ipv4.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 sock *sk,
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(sk, 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(sk, &ip6h->saddr, &tmp)) {
struct in6_addr *buf = &tmp.addr;
int i;
for (i = 0; i < 4; i++)
buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
return __tcp_fastopen_cookie_gen(sk, buf, foc);
}
}
#endif
return false;
}
/* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
* queue this additional data / FIN.
*/
void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
return;
skb = skb_clone(skb, GFP_ATOMIC);
if (!skb)
return;
skb_dst_drop(skb);
/* segs_in has been initialized to 1 in tcp_create_openreq_child().
* Hence, reset segs_in to 0 before calling tcp_segs_in()
* to avoid double counting. Also, tcp_segs_in() expects
* skb->len to include the tcp_hdrlen. Hence, it should
* be called before __skb_pull().
*/
tp->segs_in = 0;
tcp_segs_in(tp, skb);
__skb_pull(skb, tcp_hdrlen(skb));
sk_forced_mem_schedule(sk, skb->truesize);
skb_set_owner_r(skb, sk);
TCP_SKB_CB(skb)->seq++;
TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
__skb_queue_tail(&sk->sk_receive_queue, skb);
tp->syn_data_acked = 1;
/* u64_stats_update_begin(&tp->syncp) not needed here,
* as we certainly are not changing upper 32bit value (0)
*/
tp->bytes_received = skb->len;
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
tcp_fin(sk);
}
static struct sock *tcp_fastopen_create_child(struct sock *sk,
struct sk_buff *skb,
struct request_sock *req)
{
struct tcp_sock *tp;
struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
struct sock *child;
bool own_req;
child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
NULL, &own_req);
if (!child)
return NULL;
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;
tcp_rsk(req)->tfo_listener = true;
/* RFC1323: The window in SYN & SYN/ACK segments is never
* scaled. So correct it appropriately.
*/
tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
tp->max_window = tp->snd_wnd;
/* Activate the retrans timer so that SYNACK can be retransmitted.
* The request socket is not added to the ehash
* 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);
refcount_set(&req->rsk_refcnt, 2);
/* Now finish processing the fastopen child socket. */
tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
tcp_fastopen_add_skb(child, skb);
tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
tp->rcv_wup = tp->rcv_nxt;
/* tcp_conn_request() is sending the SYNACK,
* and queues the child into listener accept queue.
*/
return 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->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 || time_after(req1->rsk_timer.expires, jiffies)) {
__NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
spin_unlock(&fastopenq->lock);
return false;
}
fastopenq->rskq_rst_head = req1->dl_next;
fastopenq->qlen--;
spin_unlock(&fastopenq->lock);
reqsk_put(req1);
}
return true;
}
static bool tcp_fastopen_no_cookie(const struct sock *sk,
const struct dst_entry *dst,
int flag)
{
return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
tcp_sk(sk)->fastopen_no_cookie ||
(dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
}
/* 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).
*/
struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
struct tcp_fastopen_cookie *foc,
const struct dst_entry *dst)
{
bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
struct tcp_fastopen_cookie valid_foc = { .len = -1 };
struct sock *child;
if (foc->len == 0) /* Client requests a cookie */
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
(syn_data || foc->len >= 0) &&
tcp_fastopen_queue_check(sk))) {
foc->len = -1;
return NULL;
}
if (syn_data &&
tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
goto fastopen;
if (foc->len >= 0 && /* Client presents or requests a cookie */
tcp_fastopen_cookie_gen(sk, 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:
child = tcp_fastopen_create_child(sk, skb, req);
if (child) {
foc->len = -1;
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPFASTOPENPASSIVE);
return child;
}
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
} else if (foc->len > 0) /* Client presents an invalid cookie */
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
valid_foc.exp = foc->exp;
*foc = valid_foc;
return NULL;
}
bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
struct tcp_fastopen_cookie *cookie)
{
const struct dst_entry *dst;
tcp_fastopen_cache_get(sk, mss, cookie);
/* Firewall blackhole issue check */
if (tcp_fastopen_active_should_disable(sk)) {
cookie->len = -1;
return false;
}
dst = __sk_dst_get(sk);
if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
cookie->len = -1;
return true;
}
return cookie->len > 0;
}
/* This function checks if we want to defer sending SYN until the first
* write(). We defer under the following conditions:
* 1. fastopen_connect sockopt is set
* 2. we have a valid cookie
* Return value: return true if we want to defer until application writes data
* return false if we want to send out SYN immediately
*/
bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
{
struct tcp_fastopen_cookie cookie = { .len = 0 };
struct tcp_sock *tp = tcp_sk(sk);
u16 mss;
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);
atomic_inc(&net->ipv4.tfo_active_disable_times);
net->ipv4.tfo_active_disable_stamp = jiffies;
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);
}
}