Release 4.11 net/kcm/kcmsock.c

/*
 * Kernel Connection Multiplexor
 *
 * Copyright (c) 2016 Tom Herbert <tom@herbertland.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation.
 */

#include <linux/bpf.h>
#include <linux/errno.h>
#include <linux/errqueue.h>
#include <linux/file.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/rculist.h>
#include <linux/skbuff.h>
#include <linux/socket.h>
#include <linux/uaccess.h>
#include <linux/workqueue.h>
#include <linux/syscalls.h>
#include <linux/sched/signal.h>

#include <net/kcm.h>
#include <net/netns/generic.h>
#include <net/sock.h>
#include <uapi/linux/kcm.h>


unsigned int kcm_net_id;


static struct kmem_cache *kcm_psockp __read_mostly;

static struct kmem_cache *kcm_muxp __read_mostly;

static struct workqueue_struct *kcm_wq;



static inline struct kcm_sock *kcm_sk(const struct sock *sk)
{
	return (struct kcm_sock *)sk;
}

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static inline struct kcm_tx_msg *kcm_tx_msg(struct sk_buff *skb)
{
	return (struct kcm_tx_msg *)skb->cb;
}

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static void report_csk_error(struct sock *csk, int err)
{
	csk->sk_err = EPIPE;
	csk->sk_error_report(csk);
}

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static void kcm_abort_tx_psock(struct kcm_psock *psock, int err,
			       bool wakeup_kcm)
{
	struct sock *csk = psock->sk;
	struct kcm_mux *mux = psock->mux;

	/* Unrecoverable error in transmit */

	spin_lock_bh(&mux->lock);

	if (psock->tx_stopped) {
		spin_unlock_bh(&mux->lock);
		return;
	}

	psock->tx_stopped = 1;
	KCM_STATS_INCR(psock->stats.tx_aborts);

	if (!psock->tx_kcm) {
		/* Take off psocks_avail list */
		list_del(&psock->psock_avail_list);
	} else if (wakeup_kcm) {
		/* In this case psock is being aborted while outside of
                 * write_msgs and psock is reserved. Schedule tx_work
                 * to handle the failure there. Need to commit tx_stopped
                 * before queuing work.
                 */
		smp_mb();

		queue_work(kcm_wq, &psock->tx_kcm->tx_work);
	}

	spin_unlock_bh(&mux->lock);

	/* Report error on lower socket */
	report_csk_error(csk, err);
}

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/* RX mux lock held. */


static void kcm_update_rx_mux_stats(struct kcm_mux *mux,
				    struct kcm_psock *psock)
{
	STRP_STATS_ADD(mux->stats.rx_bytes,
		       psock->strp.stats.rx_bytes -
		       psock->saved_rx_bytes);
	mux->stats.rx_msgs +=
		psock->strp.stats.rx_msgs - psock->saved_rx_msgs;
	psock->saved_rx_msgs = psock->strp.stats.rx_msgs;
	psock->saved_rx_bytes = psock->strp.stats.rx_bytes;
}

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static void kcm_update_tx_mux_stats(struct kcm_mux *mux,
				    struct kcm_psock *psock)
{
	KCM_STATS_ADD(mux->stats.tx_bytes,
		      psock->stats.tx_bytes - psock->saved_tx_bytes);
	mux->stats.tx_msgs +=
		psock->stats.tx_msgs - psock->saved_tx_msgs;
	psock->saved_tx_msgs = psock->stats.tx_msgs;
	psock->saved_tx_bytes = psock->stats.tx_bytes;
}

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static int kcm_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);

/* KCM is ready to receive messages on its queue-- either the KCM is new or
 * has become unblocked after being blocked on full socket buffer. Queue any
 * pending ready messages on a psock. RX mux lock held.
 */


static void kcm_rcv_ready(struct kcm_sock *kcm)
{
	struct kcm_mux *mux = kcm->mux;
	struct kcm_psock *psock;
	struct sk_buff *skb;

	if (unlikely(kcm->rx_wait || kcm->rx_psock || kcm->rx_disabled))
		return;

	while (unlikely((skb = __skb_dequeue(&mux->rx_hold_queue)))) {
		if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
			/* Assuming buffer limit has been reached */
			skb_queue_head(&mux->rx_hold_queue, skb);
			WARN_ON(!sk_rmem_alloc_get(&kcm->sk));
			return;
		}
	}

	while (!list_empty(&mux->psocks_ready)) {
		psock = list_first_entry(&mux->psocks_ready, struct kcm_psock,
					 psock_ready_list);

		if (kcm_queue_rcv_skb(&kcm->sk, psock->ready_rx_msg)) {
			/* Assuming buffer limit has been reached */
			WARN_ON(!sk_rmem_alloc_get(&kcm->sk));
			return;
		}

		/* Consumed the ready message on the psock. Schedule rx_work to
                 * get more messages.
                 */
		list_del(&psock->psock_ready_list);
		psock->ready_rx_msg = NULL;
		/* Commit clearing of ready_rx_msg for queuing work */
		smp_mb();

		strp_unpause(&psock->strp);
		strp_check_rcv(&psock->strp);
	}

	/* Buffer limit is okay now, add to ready list */
	list_add_tail(&kcm->wait_rx_list,
		      &kcm->mux->kcm_rx_waiters);
	kcm->rx_wait = true;
}

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static void kcm_rfree(struct sk_buff *skb)
{
	struct sock *sk = skb->sk;
	struct kcm_sock *kcm = kcm_sk(sk);
	struct kcm_mux *mux = kcm->mux;
	unsigned int len = skb->truesize;

	sk_mem_uncharge(sk, len);
	atomic_sub(len, &sk->sk_rmem_alloc);

	/* For reading rx_wait and rx_psock without holding lock */
	smp_mb__after_atomic();

	if (!kcm->rx_wait && !kcm->rx_psock &&
	    sk_rmem_alloc_get(sk) < sk->sk_rcvlowat) {
		spin_lock_bh(&mux->rx_lock);
		kcm_rcv_ready(kcm);
		spin_unlock_bh(&mux->rx_lock);
	}
}

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static int kcm_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
{
	struct sk_buff_head *list = &sk->sk_receive_queue;

	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
		return -ENOMEM;

	if (!sk_rmem_schedule(sk, skb, skb->truesize))
		return -ENOBUFS;

	skb->dev = NULL;

	skb_orphan(skb);
	skb->sk = sk;
	skb->destructor = kcm_rfree;
	atomic_add(skb->truesize, &sk->sk_rmem_alloc);
	sk_mem_charge(sk, skb->truesize);

	skb_queue_tail(list, skb);

	if (!sock_flag(sk, SOCK_DEAD))
		sk->sk_data_ready(sk);

	return 0;
}

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/* Requeue received messages for a kcm socket to other kcm sockets. This is
 * called with a kcm socket is receive disabled.
 * RX mux lock held.
 */


static void requeue_rx_msgs(struct kcm_mux *mux, struct sk_buff_head *head)
{
	struct sk_buff *skb;
	struct kcm_sock *kcm;

	while ((skb = __skb_dequeue(head))) {
		/* Reset destructor to avoid calling kcm_rcv_ready */
		skb->destructor = sock_rfree;
		skb_orphan(skb);
try_again:
		if (list_empty(&mux->kcm_rx_waiters)) {
			skb_queue_tail(&mux->rx_hold_queue, skb);
			continue;
		}

		kcm = list_first_entry(&mux->kcm_rx_waiters,
				       struct kcm_sock, wait_rx_list);

		if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
			/* Should mean socket buffer full */
			list_del(&kcm->wait_rx_list);
			kcm->rx_wait = false;

			/* Commit rx_wait to read in kcm_free */
			smp_wmb();

			goto try_again;
		}
	}
}

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/* Lower sock lock held */


static struct kcm_sock *reserve_rx_kcm(struct kcm_psock *psock,
				       struct sk_buff *head)
{
	struct kcm_mux *mux = psock->mux;
	struct kcm_sock *kcm;

	WARN_ON(psock->ready_rx_msg);

	if (psock->rx_kcm)
		return psock->rx_kcm;

	spin_lock_bh(&mux->rx_lock);

	if (psock->rx_kcm) {
		spin_unlock_bh(&mux->rx_lock);
		return psock->rx_kcm;
	}

	kcm_update_rx_mux_stats(mux, psock);

	if (list_empty(&mux->kcm_rx_waiters)) {
		psock->ready_rx_msg = head;
		strp_pause(&psock->strp);
		list_add_tail(&psock->psock_ready_list,
			      &mux->psocks_ready);
		spin_unlock_bh(&mux->rx_lock);
		return NULL;
	}

	kcm = list_first_entry(&mux->kcm_rx_waiters,
			       struct kcm_sock, wait_rx_list);
	list_del(&kcm->wait_rx_list);
	kcm->rx_wait = false;

	psock->rx_kcm = kcm;
	kcm->rx_psock = psock;

	spin_unlock_bh(&mux->rx_lock);

	return kcm;
}

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static void kcm_done(struct kcm_sock *kcm);



static void kcm_done_work(struct work_struct *w)
{
	kcm_done(container_of(w, struct kcm_sock, done_work));
}

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/* Lower sock held */


static void unreserve_rx_kcm(struct kcm_psock *psock,
			     bool rcv_ready)
{
	struct kcm_sock *kcm = psock->rx_kcm;
	struct kcm_mux *mux = psock->mux;

	if (!kcm)
		return;

	spin_lock_bh(&mux->rx_lock);

	psock->rx_kcm = NULL;
	kcm->rx_psock = NULL;

	/* Commit kcm->rx_psock before sk_rmem_alloc_get to sync with
         * kcm_rfree
         */
	smp_mb();

	if (unlikely(kcm->done)) {
		spin_unlock_bh(&mux->rx_lock);

		/* Need to run kcm_done in a task since we need to qcquire
                 * callback locks which may already be held here.
                 */
		INIT_WORK(&kcm->done_work, kcm_done_work);
		schedule_work(&kcm->done_work);
		return;
	}

	if (unlikely(kcm->rx_disabled)) {
		requeue_rx_msgs(mux, &kcm->sk.sk_receive_queue);
	} else if (rcv_ready || unlikely(!sk_rmem_alloc_get(&kcm->sk))) {
		/* Check for degenerative race with rx_wait that all
                 * data was dequeued (accounted for in kcm_rfree).
                 */
		kcm_rcv_ready(kcm);
	}
	spin_unlock_bh(&mux->rx_lock);
}

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/* Lower sock lock held */


static void psock_data_ready(struct sock *sk)
{
	struct kcm_psock *psock;

	read_lock_bh(&sk->sk_callback_lock);

	psock = (struct kcm_psock *)sk->sk_user_data;
	if (likely(psock))
		strp_data_ready(&psock->strp);

	read_unlock_bh(&sk->sk_callback_lock);
}

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/* Called with lower sock held */


static void kcm_rcv_strparser(struct strparser *strp, struct sk_buff *skb)
{
	struct kcm_psock *psock = container_of(strp, struct kcm_psock, strp);
	struct kcm_sock *kcm;

try_queue:
	kcm = reserve_rx_kcm(psock, skb);
	if (!kcm) {
		 /* Unable to reserve a KCM, message is held in psock and strp
                  * is paused.
                  */
		return;
	}

	if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
		/* Should mean socket buffer full */
		unreserve_rx_kcm(psock, false);
		goto try_queue;
	}
}

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static int kcm_parse_func_strparser(struct strparser *strp, struct sk_buff *skb)
{
	struct kcm_psock *psock = container_of(strp, struct kcm_psock, strp);
	struct bpf_prog *prog = psock->bpf_prog;

	return (*prog->bpf_func)(skb, prog->insnsi);
}

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static int kcm_read_sock_done(struct strparser *strp, int err)
{
	struct kcm_psock *psock = container_of(strp, struct kcm_psock, strp);

	unreserve_rx_kcm(psock, true);

	return err;
}

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static void psock_state_change(struct sock *sk)
{
	/* TCP only does a POLLIN for a half close. Do a POLLHUP here
         * since application will normally not poll with POLLIN
         * on the TCP sockets.
         */

	report_csk_error(sk, EPIPE);
}

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static void psock_write_space(struct sock *sk)
{
	struct kcm_psock *psock;
	struct kcm_mux *mux;
	struct kcm_sock *kcm;

	read_lock_bh(&sk->sk_callback_lock);

	psock = (struct kcm_psock *)sk->sk_user_data;
	if (unlikely(!psock))
		goto out;
	mux = psock->mux;

	spin_lock_bh(&mux->lock);

	/* Check if the socket is reserved so someone is waiting for sending. */
	kcm = psock->tx_kcm;
	if (kcm && !unlikely(kcm->tx_stopped))
		queue_work(kcm_wq, &kcm->tx_work);

	spin_unlock_bh(&mux->lock);
out:
	read_unlock_bh(&sk->sk_callback_lock);
}

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static void unreserve_psock(struct kcm_sock *kcm);

/* kcm sock is locked. */


static struct kcm_psock *reserve_psock(struct kcm_sock *kcm)
{
	struct kcm_mux *mux = kcm->mux;
	struct kcm_psock *psock;

	psock = kcm->tx_psock;

	smp_rmb(); /* Must read tx_psock before tx_wait */

	if (psock) {
		WARN_ON(kcm->tx_wait);
		if (unlikely(psock->tx_stopped))
			unreserve_psock(kcm);
		else
			return kcm->tx_psock;
	}

	spin_lock_bh(&mux->lock);

	/* Check again under lock to see if psock was reserved for this
         * psock via psock_unreserve.
         */
	psock = kcm->tx_psock;
	if (unlikely(psock)) {
		WARN_ON(kcm->tx_wait);
		spin_unlock_bh(&mux->lock);
		return kcm->tx_psock;
	}

	if (!list_empty(&mux->psocks_avail)) {
		psock = list_first_entry(&mux->psocks_avail,
					 struct kcm_psock,
					 psock_avail_list);
		list_del(&psock->psock_avail_list);
		if (kcm->tx_wait) {
			list_del(&kcm->wait_psock_list);
			kcm->tx_wait = false;
		}
		kcm->tx_psock = psock;
		psock->tx_kcm = kcm;
		KCM_STATS_INCR(psock->stats.reserved);
	} else if (!kcm->tx_wait) {
		list_add_tail(&kcm->wait_psock_list,
			      &mux->kcm_tx_waiters);
		kcm->tx_wait = true;
	}

	spin_unlock_bh(&mux->lock);

	return psock;
}

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/* mux lock held */


static void psock_now_avail(struct kcm_psock *psock)
{
	struct kcm_mux *mux = psock->mux;
	struct kcm_sock *kcm;

	if (list_empty(&mux->kcm_tx_waiters)) {
		list_add_tail(&psock->psock_avail_list,
			      &mux->psocks_avail);
	} else {
		kcm = list_first_entry(&mux->kcm_tx_waiters,
				       struct kcm_sock,
				       wait_psock_list);
		list_del(&kcm->wait_psock_list);
		kcm->tx_wait = false;
		psock->tx_kcm = kcm;

		/* Commit before changing tx_psock since that is read in
                 * reserve_psock before queuing work.
                 */
		smp_mb();

		kcm->tx_psock = psock;
		KCM_STATS_INCR(psock->stats.reserved);
		queue_work(kcm_wq, &kcm->tx_work);
	}
}

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/* kcm sock is locked. */


static void unreserve_psock(struct kcm_sock *kcm)
{
	struct kcm_psock *psock;
	struct kcm_mux *mux = kcm->mux;

	spin_lock_bh(&mux->lock);

	psock = kcm->tx_psock;

	if (WARN_ON(!psock)) {
		spin_unlock_bh(&mux->lock);
		return;
	}

	smp_rmb(); /* Read tx_psock before tx_wait */

	kcm_update_tx_mux_stats(mux, psock);

	WARN_ON(kcm->tx_wait);

	kcm->tx_psock = NULL;
	psock->tx_kcm = NULL;
	KCM_STATS_INCR(psock->stats.unreserved);

	if (unlikely(psock->tx_stopped)) {
		if (psock->done) {
			/* Deferred free */
			list_del(&psock->psock_list);
			mux->psocks_cnt--;
			sock_put(psock->sk);
			fput(psock->sk->sk_socket->file);
			kmem_cache_free(kcm_psockp, psock);
		}

		/* Don't put back on available list */

		spin_unlock_bh(&mux->lock);

		return;
	}

	psock_now_avail(psock);

	spin_unlock_bh(&mux->lock);
}

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static void kcm_report_tx_retry(struct kcm_sock *kcm)
{
	struct kcm_mux *mux = kcm->mux;

	spin_lock_bh(&mux->lock);
	KCM_STATS_INCR(mux->stats.tx_retries);
	spin_unlock_bh(&mux->lock);
}

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/* Write any messages ready on the kcm socket.  Called with kcm sock lock
 * held.  Return bytes actually sent or error.
 */


static int kcm_write_msgs(struct kcm_sock *kcm)
{
	struct sock *sk = &kcm->sk;
	struct kcm_psock *psock;
	struct sk_buff *skb, *head;
	struct kcm_tx_msg *txm;
	unsigned short fragidx, frag_offset;
	unsigned int sent, total_sent = 0;
	int ret = 0;

	kcm->tx_wait_more = false;
	psock = kcm->tx_psock;
	if (unlikely(psock && psock->tx_stopped)) {
		/* A reserved psock was aborted asynchronously. Unreserve
                 * it and we'll retry the message.
                 */
		unreserve_psock(kcm);
		kcm_report_tx_retry(kcm);
		if (skb_queue_empty(&sk->sk_write_queue))
			return 0;

		kcm_tx_msg(skb_peek(&sk->sk_write_queue))->sent = 0;

	} else if (skb_queue_empty(&sk->sk_write_queue)) {
		return 0;
	}

	head = skb_peek(&sk->sk_write_queue);
	txm = kcm_tx_msg(head);

	if (txm->sent) {
		/* Send of first skbuff in queue already in progress */
		if (WARN_ON(!psock)) {
			ret = -EINVAL;
			goto out;
		}
		sent = txm->sent;
		frag_offset = txm->frag_offset;
		fragidx = txm->fragidx;
		skb = txm->frag_skb;

		goto do_frag;
	}

try_again:
	psock = reserve_psock(kcm);
	if (!psock)
		goto out;

	do {
		skb = head;
		txm = kcm_tx_msg(head);
		sent = 0;

do_frag_list:
		if (WARN_ON(!skb_shinfo(skb)->nr_frags)) {
			ret = -EINVAL;
			goto out;
		}

		for (fragidx = 0; fragidx < skb_shinfo(skb)->nr_frags;
		     fragidx++) {
			skb_frag_t *frag;

			frag_offset = 0;
do_frag:
			frag = &skb_shinfo(skb)->frags[fragidx];
			if (WARN_ON(!frag->size)) {
				ret = -EINVAL;
				goto out;
			}

			ret = kernel_sendpage(psock->sk->sk_socket,
					      frag->page.p,
					      frag->page_offset + frag_offset,
					      frag->size - frag_offset,
					      MSG_DONTWAIT);
			if (ret <= 0) {
				if (ret == -EAGAIN) {
					/* Save state to try again when there's
                                         * write space on the socket
                                         */
					txm->sent = sent;
					txm->frag_offset = frag_offset;
					txm->fragidx = fragidx;
					txm->frag_skb = skb;

					ret = 0;
					goto out;
				}

				/* Hard failure in sending message, abort this
                                 * psock since it has lost framing
                                 * synchonization and retry sending the
                                 * message from the beginning.
                                 */
				kcm_abort_tx_psock(psock, ret ? -ret : EPIPE,
						   true);
				unreserve_psock(kcm);

				txm->sent = 0;
				kcm_report_tx_retry(kcm);
				ret = 0;

				goto try_again;
			}

			sent += ret;
			frag_offset += ret;
			KCM_STATS_ADD(psock->stats.tx_bytes, ret);
			if (frag_offset < frag->size) {
				/* Not finished with this frag */
				goto do_frag;
			}
		}

		if (skb == head) {
			if (skb_has_frag_list(skb)) {
				skb = skb_shinfo(skb)->frag_list;
				goto do_frag_list;
			}
		} else if (skb->next) {
			skb = skb->next;
			goto do_frag_list;
		}

		/* Successfully sent the whole packet, account for it. */
		skb_dequeue(&sk->sk_write_queue);
		kfree_skb(head);
		sk->sk_wmem_queued -= sent;
		total_sent += sent;
		KCM_STATS_INCR(psock->stats.tx_msgs);
	} while ((head = skb_peek(&sk->sk_write_queue)));
out:
	if (!head) {
		/* Done with all queued messages. */
		WARN_ON(!skb_queue_empty(&sk->sk_write_queue));
		unreserve_psock(kcm);
	}

	/* Check if write space is available */
	sk->sk_write_space(sk);

	return total_sent ? : ret;
}

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static void kcm_tx_work(struct work_struct *w)
{
	struct kcm_sock *kcm = container_of(w, struct kcm_sock, tx_work);
	struct sock *sk = &kcm->sk;
	int err;

	lock_sock(sk);

	/* Primarily for SOCK_DGRAM sockets, also handle asynchronous tx
         * aborts
         */
	err = kcm_write_msgs(kcm);
	if (err < 0) {
		/* Hard failure in write, report error on KCM socket */
		pr_warn("KCM: Hard failure on kcm_write_msgs %d\n", err);
		report_csk_error(&kcm->sk, -err);
		goto out;
	}

	/* Primarily for SOCK_SEQPACKET sockets */
	if (likely(sk->sk_socket) &&
	    test_bit(SOCK_NOSPACE, &sk