tcp: move reqsk_fastopen_remove to net/ipv4/tcp_fastopen.c (a90765c6) · Commits · git / linux-net

net/core/request_sock.c

+0 −85

Original line number	Diff line number	Diff line
		@@ -16,88 +16,3 @@

		#include <net/request_sock.h>

		/*
		* This function is called to set a Fast Open socket's "fastopen_rsk" field
		* to NULL when a TFO socket no longer needs to access the request_sock.
		* This happens only after 3WHS has been either completed or aborted (e.g.,
		* RST is received).
		*
		* Before TFO, a child socket is created only after 3WHS is completed,
		* hence it never needs to access the request_sock. things get a lot more
		* complex with TFO. A child socket, accepted or not, has to access its
		* request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
		* until 3WHS is either completed or aborted. Afterwards the req will stay
		* until either the child socket is accepted, or in the rare case when the
		* listener is closed before the child is accepted.
		*
		* In short, a request socket is only freed after BOTH 3WHS has completed
		* (or aborted) and the child socket has been accepted (or listener closed).
		* When a child socket is accepted, its corresponding req->sk is set to
		* NULL since it's no longer needed. More importantly, "req->sk == NULL"
		* will be used by the code below to determine if a child socket has been
		* accepted or not, and the check is protected by the fastopenq->lock
		* described below.
		*
		* Note that fastopen_rsk is only accessed from the child socket's context
		* with its socket lock held. But a request_sock (req) can be accessed by
		* both its child socket through fastopen_rsk, and a listener socket through
		* icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
		* lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
		* only in the rare case when both the listener and the child locks are held,
		* e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
		* The lock also protects other fields such as fastopenq->qlen, which is
		* decremented by this function when fastopen_rsk is no longer needed.
		*
		* Note that another solution was to simply use the existing socket lock
		* from the listener. But first socket lock is difficult to use. It is not
		* a simple spin lock - one must consider sock_owned_by_user() and arrange
		* to use sk_add_backlog() stuff. But what really makes it infeasible is the
		* locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
		* acquire a child's lock while holding listener's socket lock.
		*
		* This function also sets "treq->tfo_listener" to false.
		* treq->tfo_listener is used by the listener so it is protected by the
		* fastopenq->lock in this function.
		*/
		void reqsk_fastopen_remove(struct sock sk, struct request_sock req,
		bool reset)
		{
		struct sock *lsk = req->rsk_listener;
		struct fastopen_queue *fastopenq;

		fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;

		RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL);
		spin_lock_bh(&fastopenq->lock);
		fastopenq->qlen--;
		tcp_rsk(req)->tfo_listener = false;
		if (req->sk) /* the child socket hasn't been accepted yet */
		goto out;

		if (!reset \|\| lsk->sk_state != TCP_LISTEN) {
		/* If the listener has been closed don't bother with the
		* special RST handling below.
		*/
		spin_unlock_bh(&fastopenq->lock);
		reqsk_put(req);
		return;
		}
		/* Wait for 60secs before removing a req that has triggered RST.
		* This is a simple defense against TFO spoofing attack - by
		* counting the req against fastopen.max_qlen, and disabling
		* TFO when the qlen exceeds max_qlen.
		*
		* For more details see CoNext'11 "TCP Fast Open" paper.
		*/
		req->rsk_timer.expires = jiffies + 60*HZ;
		if (fastopenq->rskq_rst_head == NULL)
		fastopenq->rskq_rst_head = req;
		else
		fastopenq->rskq_rst_tail->dl_next = req;

		req->dl_next = NULL;
		fastopenq->rskq_rst_tail = req;
		fastopenq->qlen++;
		out:
		spin_unlock_bh(&fastopenq->lock);
		}

net/ipv4/tcp_fastopen.c

+86 −0

Original line number	Diff line number	Diff line
		@@ -5,6 +5,92 @@
		#include <net/tcp.h>
		#include <net/busy_poll.h>

		/*
		* This function is called to set a Fast Open socket's "fastopen_rsk" field
		* to NULL when a TFO socket no longer needs to access the request_sock.
		* This happens only after 3WHS has been either completed or aborted (e.g.,
		* RST is received).
		*
		* Before TFO, a child socket is created only after 3WHS is completed,
		* hence it never needs to access the request_sock. things get a lot more
		* complex with TFO. A child socket, accepted or not, has to access its
		* request_sock for 3WHS processing, e.g., to retransmit SYN-ACK pkts,
		* until 3WHS is either completed or aborted. Afterwards the req will stay
		* until either the child socket is accepted, or in the rare case when the
		* listener is closed before the child is accepted.
		*
		* In short, a request socket is only freed after BOTH 3WHS has completed
		* (or aborted) and the child socket has been accepted (or listener closed).
		* When a child socket is accepted, its corresponding req->sk is set to
		* NULL since it's no longer needed. More importantly, "req->sk == NULL"
		* will be used by the code below to determine if a child socket has been
		* accepted or not, and the check is protected by the fastopenq->lock
		* described below.
		*
		* Note that fastopen_rsk is only accessed from the child socket's context
		* with its socket lock held. But a request_sock (req) can be accessed by
		* both its child socket through fastopen_rsk, and a listener socket through
		* icsk_accept_queue.rskq_accept_head. To protect the access a simple spin
		* lock per listener "icsk->icsk_accept_queue.fastopenq->lock" is created.
		* only in the rare case when both the listener and the child locks are held,
		* e.g., in inet_csk_listen_stop() do we not need to acquire the lock.
		* The lock also protects other fields such as fastopenq->qlen, which is
		* decremented by this function when fastopen_rsk is no longer needed.
		*
		* Note that another solution was to simply use the existing socket lock
		* from the listener. But first socket lock is difficult to use. It is not
		* a simple spin lock - one must consider sock_owned_by_user() and arrange
		* to use sk_add_backlog() stuff. But what really makes it infeasible is the
		* locking hierarchy violation. E.g., inet_csk_listen_stop() may try to
		* acquire a child's lock while holding listener's socket lock.
		*
		* This function also sets "treq->tfo_listener" to false.
		* treq->tfo_listener is used by the listener so it is protected by the
		* fastopenq->lock in this function.
		*/
		void reqsk_fastopen_remove(struct sock sk, struct request_sock req,
		bool reset)
		{
		struct sock *lsk = req->rsk_listener;
		struct fastopen_queue *fastopenq;

		fastopenq = &inet_csk(lsk)->icsk_accept_queue.fastopenq;

		RCU_INIT_POINTER(tcp_sk(sk)->fastopen_rsk, NULL);
		spin_lock_bh(&fastopenq->lock);
		fastopenq->qlen--;
		tcp_rsk(req)->tfo_listener = false;
		if (req->sk) /* the child socket hasn't been accepted yet */
		goto out;

		if (!reset \|\| lsk->sk_state != TCP_LISTEN) {
		/* If the listener has been closed don't bother with the
		* special RST handling below.
		*/
		spin_unlock_bh(&fastopenq->lock);
		reqsk_put(req);
		return;
		}
		/* Wait for 60secs before removing a req that has triggered RST.
		* This is a simple defense against TFO spoofing attack - by
		* counting the req against fastopen.max_qlen, and disabling
		* TFO when the qlen exceeds max_qlen.
		*
		* For more details see CoNext'11 "TCP Fast Open" paper.
		*/
		req->rsk_timer.expires = jiffies + 60*HZ;
		if (fastopenq->rskq_rst_head == NULL)
		fastopenq->rskq_rst_head = req;
		else
		fastopenq->rskq_rst_tail->dl_next = req;

		req->dl_next = NULL;
		fastopenq->rskq_rst_tail = req;
		fastopenq->qlen++;
		out:
		spin_unlock_bh(&fastopenq->lock);
		}

		void tcp_fastopen_init_key_once(struct net *net)
		{
		u8 key[TCP_FASTOPEN_KEY_LENGTH];