133 lines
5.0 KiB
C
133 lines
5.0 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* NET Generic infrastructure for Network protocols.
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*
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* Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
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*
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* From code originally in include/net/tcp.h
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*/
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#include <linux/module.h>
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#include <linux/random.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/tcp.h>
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#include <linux/vmalloc.h>
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#include <net/request_sock.h>
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/*
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* Maximum number of SYN_RECV sockets in queue per LISTEN socket.
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* One SYN_RECV socket costs about 80bytes on a 32bit machine.
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* It would be better to replace it with a global counter for all sockets
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* but then some measure against one socket starving all other sockets
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* would be needed.
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*
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* The minimum value of it is 128. Experiments with real servers show that
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* it is absolutely not enough even at 100conn/sec. 256 cures most
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* of problems.
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* This value is adjusted to 128 for low memory machines,
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* and it will increase in proportion to the memory of machine.
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* Note : Dont forget somaxconn that may limit backlog too.
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*/
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void reqsk_queue_alloc(struct request_sock_queue *queue)
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{
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spin_lock_init(&queue->rskq_lock);
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spin_lock_init(&queue->fastopenq.lock);
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queue->fastopenq.rskq_rst_head = NULL;
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queue->fastopenq.rskq_rst_tail = NULL;
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queue->fastopenq.qlen = 0;
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queue->rskq_accept_head = NULL;
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}
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/*
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* This function is called to set a Fast Open socket's "fastopen_rsk" field
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* to NULL when a TFO socket no longer needs to access the request_sock.
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* This happens only after 3WHS has been either completed or aborted (e.g.,
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* RST is received).
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*
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* Before TFO, a child socket is created only after 3WHS is completed,
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* hence it never needs to access the request_sock. things get a lot more
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* complex with TFO. A child socket, accepted or not, has to access its
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* request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
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* until 3WHS is either completed or aborted. Afterwards the req will stay
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* until either the child socket is accepted, or in the rare case when the
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* listener is closed before the child is accepted.
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*
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* In short, a request socket is only freed after BOTH 3WHS has completed
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* (or aborted) and the child socket has been accepted (or listener closed).
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* When a child socket is accepted, its corresponding req->sk is set to
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* NULL since it's no longer needed. More importantly, "req->sk == NULL"
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* will be used by the code below to determine if a child socket has been
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* accepted or not, and the check is protected by the fastopenq->lock
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* described below.
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*
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* Note that fastopen_rsk is only accessed from the child socket's context
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* with its socket lock held. But a request_sock (req) can be accessed by
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* both its child socket through fastopen_rsk, and a listener socket through
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* icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
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* lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
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* only in the rare case when both the listener and the child locks are held,
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* e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
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* The lock also protects other fields such as fastopenq->qlen, which is
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* decremented by this function when fastopen_rsk is no longer needed.
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*
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* Note that another solution was to simply use the existing socket lock
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* from the listener. But first socket lock is difficult to use. It is not
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* a simple spin lock - one must consider sock_owned_by_user() and arrange
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* to use sk_add_backlog() stuff. But what really makes it infeasible is the
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* locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
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* acquire a child's lock while holding listener's socket lock. A corner
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* case might also exist in tcp_v4_hnd_req() that will trigger this locking
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* order.
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*
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* This function also sets "treq->tfo_listener" to false.
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* treq->tfo_listener is used by the listener so it is protected by the
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* fastopenq->lock in this function.
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*/
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void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
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bool reset)
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{
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struct sock *lsk = req->rsk_listener;
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struct fastopen_queue *fastopenq;
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fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;
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RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL);
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spin_lock_bh(&fastopenq->lock);
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fastopenq->qlen--;
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tcp_rsk(req)->tfo_listener = false;
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if (req->sk) /* the child socket hasn't been accepted yet */
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goto out;
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if (!reset || lsk->sk_state != TCP_LISTEN) {
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/* If the listener has been closed don't bother with the
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* special RST handling below.
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*/
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spin_unlock_bh(&fastopenq->lock);
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reqsk_put(req);
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return;
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}
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/* Wait for 60secs before removing a req that has triggered RST.
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* This is a simple defense against TFO spoofing attack - by
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* counting the req against fastopen.max_qlen, and disabling
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* TFO when the qlen exceeds max_qlen.
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*
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* For more details see CoNext'11 "TCP Fast Open" paper.
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*/
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req->rsk_timer.expires = jiffies + 60*HZ;
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if (fastopenq->rskq_rst_head == NULL)
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fastopenq->rskq_rst_head = req;
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else
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fastopenq->rskq_rst_tail->dl_next = req;
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req->dl_next = NULL;
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fastopenq->rskq_rst_tail = req;
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fastopenq->qlen++;
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out:
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spin_unlock_bh(&fastopenq->lock);
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}
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