kcm: Kernel Connection Multiplexor module

This module implements the Kernel Connection Multiplexor.

Kernel Connection Multiplexor (KCM) is a facility that provides a
message based interface over TCP for generic application protocols.
With KCM an application can efficiently send and receive application
protocol messages over TCP using datagram sockets.

For more information see the included Documentation/networking/kcm.txt
Signed-off-by: NTom Herbert <tom@herbertland.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/socket.h

@@ -200,7 +200,9 @@ struct ucred {
 #define AF_ALG		38	/* Algorithm sockets		*/
 #define AF_NFC		39	/* NFC sockets			*/
 #define AF_VSOCK	40	/* vSockets			*/
-#define AF_MAX		41	/* For now.. */
+#define AF_KCM		41	/* Kernel Connection Multiplexor*/
+
+#define AF_MAX		42	/* For now.. */
 
 /* Protocol families, same as address families. */
 #define PF_UNSPEC	AF_UNSPEC
@@ -246,6 +248,7 @@ struct ucred {
 #define PF_ALG		AF_ALG
 #define PF_NFC		AF_NFC
 #define PF_VSOCK	AF_VSOCK
+#define PF_KCM		AF_KCM
 #define PF_MAX		AF_MAX
 
 /* Maximum queue length specifiable by listen.  */
@@ -323,6 +326,7 @@ struct ucred {
 #define SOL_CAIF	278
 #define SOL_ALG		279
 #define SOL_NFC		280
+#define SOL_KCM		281
 
 /* IPX options */
 #define IPX_TYPE	1

include/net/kcm.h

+/*
+ * 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.
+ */
+
+#ifndef __NET_KCM_H_
+#define __NET_KCM_H_
+
+#include <linux/skbuff.h>
+#include <net/sock.h>
+#include <uapi/linux/kcm.h>
+
+extern unsigned int kcm_net_id;
+
+struct kcm_tx_msg {
+	unsigned int sent;
+	unsigned int fragidx;
+	unsigned int frag_offset;
+	unsigned int msg_flags;
+	struct sk_buff *frag_skb;
+	struct sk_buff *last_skb;
+};
+
+struct kcm_rx_msg {
+	int full_len;
+	int accum_len;
+	int offset;
+};
+
+/* Socket structure for KCM client sockets */
+struct kcm_sock {
+	struct sock sk;
+	struct kcm_mux *mux;
+	struct list_head kcm_sock_list;
+	int index;
+	u32 done : 1;
+	struct work_struct done_work;
+
+	/* Transmit */
+	struct kcm_psock *tx_psock;
+	struct work_struct tx_work;
+	struct list_head wait_psock_list;
+	struct sk_buff *seq_skb;
+
+	/* Don't use bit fields here, these are set under different locks */
+	bool tx_wait;
+	bool tx_wait_more;
+
+	/* Receive */
+	struct kcm_psock *rx_psock;
+	struct list_head wait_rx_list; /* KCMs waiting for receiving */
+	bool rx_wait;
+	u32 rx_disabled : 1;
+};
+
+struct bpf_prog;
+
+/* Structure for an attached lower socket */
+struct kcm_psock {
+	struct sock *sk;
+	struct kcm_mux *mux;
+	int index;
+
+	u32 tx_stopped : 1;
+	u32 rx_stopped : 1;
+	u32 done : 1;
+	u32 unattaching : 1;
+
+	void (*save_state_change)(struct sock *sk);
+	void (*save_data_ready)(struct sock *sk);
+	void (*save_write_space)(struct sock *sk);
+
+	struct list_head psock_list;
+
+	/* Receive */
+	struct sk_buff *rx_skb_head;
+	struct sk_buff **rx_skb_nextp;
+	struct sk_buff *ready_rx_msg;
+	struct list_head psock_ready_list;
+	struct work_struct rx_work;
+	struct delayed_work rx_delayed_work;
+	struct bpf_prog *bpf_prog;
+	struct kcm_sock *rx_kcm;
+
+	/* Transmit */
+	struct kcm_sock *tx_kcm;
+	struct list_head psock_avail_list;
+};
+
+/* Per net MUX list */
+struct kcm_net {
+	struct mutex mutex;
+	struct list_head mux_list;
+	int count;
+};
+
+/* Structure for a MUX */
+struct kcm_mux {
+	struct list_head kcm_mux_list;
+	struct rcu_head rcu;
+	struct kcm_net *knet;
+
+	struct list_head kcm_socks;	/* All KCM sockets on MUX */
+	int kcm_socks_cnt;		/* Total KCM socket count for MUX */
+	struct list_head psocks;	/* List of all psocks on MUX */
+	int psocks_cnt;		/* Total attached sockets */
+
+	/* Receive */
+	spinlock_t rx_lock ____cacheline_aligned_in_smp;
+	struct list_head kcm_rx_waiters; /* KCMs waiting for receiving */
+	struct list_head psocks_ready;	/* List of psocks with a msg ready */
+	struct sk_buff_head rx_hold_queue;
+
+	/* Transmit */
+	spinlock_t  lock ____cacheline_aligned_in_smp;	/* TX and mux locking */
+	struct list_head psocks_avail;	/* List of available psocks */
+	struct list_head kcm_tx_waiters; /* KCMs waiting for a TX psock */
+};
+
+#endif /* __NET_KCM_H_ */

include/uapi/linux/kcm.h

+/*
+ * 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.
+ *
+ * User API to clone KCM sockets and attach transport socket to a KCM
+ * multiplexor.
+ */
+
+#ifndef KCM_KERNEL_H
+#define KCM_KERNEL_H
+
+struct kcm_attach {
+	int fd;
+	int bpf_fd;
+};
+
+struct kcm_unattach {
+	int fd;
+};
+
+struct kcm_clone {
+	int fd;
+};
+
+#define SIOCKCMATTACH	(SIOCPROTOPRIVATE + 0)
+#define SIOCKCMUNATTACH	(SIOCPROTOPRIVATE + 1)
+#define SIOCKCMCLONE	(SIOCPROTOPRIVATE + 2)
+
+#define KCMPROTO_CONNECTED	0
+
+/* Socket options */
+#define KCM_RECV_DISABLE	1
+
+#endif
+

net/Kconfig

@@ -360,6 +360,7 @@ source "net/can/Kconfig"
 source "net/irda/Kconfig"
 source "net/bluetooth/Kconfig"
 source "net/rxrpc/Kconfig"
+source "net/kcm/Kconfig"
 
 config FIB_RULES
 	bool

net/Makefile

@@ -34,6 +34,7 @@ obj-$(CONFIG_IRDA)		+= irda/
 obj-$(CONFIG_BT)		+= bluetooth/
 obj-$(CONFIG_SUNRPC)		+= sunrpc/
 obj-$(CONFIG_AF_RXRPC)		+= rxrpc/
+obj-$(CONFIG_AF_KCM)		+= kcm/
 obj-$(CONFIG_ATM)		+= atm/
 obj-$(CONFIG_L2TP)		+= l2tp/
 obj-$(CONFIG_DECNET)		+= decnet/

net/kcm/Kconfig

+
+config AF_KCM
+	tristate "KCM sockets"
+	depends on INET
+	select BPF_SYSCALL
+	---help---
+	  KCM (Kernel Connection Multiplexor) sockets provide a method
+	  for multiplexing messages of a message based application
+	  protocol over kernel connectons (e.g. TCP connections).
+

net/kcm/Makefile

+obj-$(CONFIG_AF_KCM) += kcm.o
+
+kcm-y := kcmsock.o

net/kcm/kcmsock.c

+#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 <net/kcm.h>
+#include <net/netns/generic.h>
+#include <net/sock.h>
+#include <net/tcp.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;
+}
+
+static inline struct kcm_tx_msg *kcm_tx_msg(struct sk_buff *skb)
+{
+	return (struct kcm_tx_msg *)skb->cb;
+}
+
+static inline struct kcm_rx_msg *kcm_rx_msg(struct sk_buff *skb)
+{
+	return (struct kcm_rx_msg *)((void *)skb->cb +
+				     offsetof(struct qdisc_skb_cb, data));
+}
+
+static void report_csk_error(struct sock *csk, int err)
+{
+	csk->sk_err = EPIPE;
+	csk->sk_error_report(csk);
+}
+
+/* Callback lock held */
+static void kcm_abort_rx_psock(struct kcm_psock *psock, int err,
+			       struct sk_buff *skb)
+{
+	struct sock *csk = psock->sk;
+
+	/* Unrecoverable error in receive */
+
+	if (psock->rx_stopped)
+		return;
+
+	psock->rx_stopped = 1;
+
+	/* Report an error on the lower socket */
+	report_csk_error(csk, err);
+}
+
+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;
+
+	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);
+}
+
+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();
+
+		queue_work(kcm_wq, &psock->rx_work);
+	}
+
+	/* 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;
+}
+
+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);
+	}
+}
+
+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;
+}
+
+/* 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;
+		}
+	}
+}
+
+/* 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;
+	}
+
+	if (list_empty(&mux->kcm_rx_waiters)) {
+		psock->ready_rx_msg = head;
+		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;
+}
+
+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));
+}
+
+/* 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);
+}
+
+/* Macro to invoke filter function. */
+#define KCM_RUN_FILTER(prog, ctx) \
+	(*prog->bpf_func)(ctx, prog->insnsi)
+
+/* Lower socket lock held */
+static int kcm_tcp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
+			unsigned int orig_offset, size_t orig_len)
+{
+	struct kcm_psock *psock = (struct kcm_psock *)desc->arg.data;
+	struct kcm_rx_msg *rxm;
+	struct kcm_sock *kcm;
+	struct sk_buff *head, *skb;
+	size_t eaten = 0, cand_len;
+	ssize_t extra;
+	int err;
+	bool cloned_orig = false;
+
+	if (psock->ready_rx_msg)
+		return 0;
+
+	head = psock->rx_skb_head;
+	if (head) {
+		/* Message already in progress */
+
+		if (unlikely(orig_offset)) {
+			/* Getting data with a non-zero offset when a message is
+			 * in progress is not expected. If it does happen, we
+			 * need to clone and pull since we can't deal with
+			 * offsets in the skbs for a message expect in the head.
+			 */
+			orig_skb = skb_clone(orig_skb, GFP_ATOMIC);
+			if (!orig_skb) {
+				desc->error = -ENOMEM;
+				return 0;
+			}
+			if (!pskb_pull(orig_skb, orig_offset)) {
+				kfree_skb(orig_skb);
+				desc->error = -ENOMEM;
+				return 0;
+			}
+			cloned_orig = true;
+			orig_offset = 0;
+		}
+
+		if (!psock->rx_skb_nextp) {
+			/* We are going to append to the frags_list of head.
+			 * Need to unshare the frag_list.
+			 */
+			err = skb_unclone(head, GFP_ATOMIC);
+			if (err) {
+				desc->error = err;
+				return 0;
+			}
+
+			if (unlikely(skb_shinfo(head)->frag_list)) {
+				/* We can't append to an sk_buff that already
+				 * has a frag_list. We create a new head, point
+				 * the frag_list of that to the old head, and
+				 * then are able to use the old head->next for
+				 * appending to the message.
+				 */
+				if (WARN_ON(head->next)) {
+					desc->error = -EINVAL;
+					return 0;
+				}
+
+				skb = alloc_skb(0, GFP_ATOMIC);
+				if (!skb) {
+					desc->error = -ENOMEM;
+					return 0;
+				}
+				skb->len = head->len;
+				skb->data_len = head->len;
+				skb->truesize = head->truesize;
+				*kcm_rx_msg(skb) = *kcm_rx_msg(head);
+				psock->rx_skb_nextp = &head->next;
+				skb_shinfo(skb)->frag_list = head;
+				psock->rx_skb_head = skb;
+				head = skb;
+			} else {
+				psock->rx_skb_nextp =
+				    &skb_shinfo(head)->frag_list;
+			}
+		}
+	}
+
+	while (eaten < orig_len) {
+		/* Always clone since we will consume something */
+		skb = skb_clone(orig_skb, GFP_ATOMIC);
+		if (!skb) {
+			desc->error = -ENOMEM;
+			break;
+		}
+
+		cand_len = orig_len - eaten;
+
+		head = psock->rx_skb_head;
+		if (!head) {
+			head = skb;
+			psock->rx_skb_head = head;
+			/* Will set rx_skb_nextp on next packet if needed */
+			psock->rx_skb_nextp = NULL;
+			rxm = kcm_rx_msg(head);
+			memset(rxm, 0, sizeof(*rxm));
+			rxm->offset = orig_offset + eaten;
+		} else {
+			/* Unclone since we may be appending to an skb that we
+			 * already share a frag_list with.
+			 */
+			err = skb_unclone(skb, GFP_ATOMIC);
+			if (err) {
+				desc->error = err;
+				break;
+			}
+
+			rxm = kcm_rx_msg(head);
+			*psock->rx_skb_nextp = skb;
+			psock->rx_skb_nextp = &skb->next;
+			head->data_len += skb->len;
+			head->len += skb->len;
+			head->truesize += skb->truesize;
+		}
+
+		if (!rxm->full_len) {
+			ssize_t len;
+
+			len = KCM_RUN_FILTER(psock->bpf_prog, head);
+
+			if (!len) {
+				/* Need more header to determine length */
+				rxm->accum_len += cand_len;
+				eaten += cand_len;
+				WARN_ON(eaten != orig_len);
+				break;
+			} else if (len <= (ssize_t)head->len -
+					  skb->len - rxm->offset) {
+				/* Length must be into new skb (and also
+				 * greater than zero)
+				 */
+				desc->error = -EPROTO;
+				psock->rx_skb_head = NULL;
+				kcm_abort_rx_psock(psock, EPROTO, head);
+				break;
+			}
+
+			rxm->full_len = len;
+		}
+
+		extra = (ssize_t)(rxm->accum_len + cand_len) - rxm->full_len;
+
+		if (extra < 0) {
+			/* Message not complete yet. */
+			rxm->accum_len += cand_len;
+			eaten += cand_len;
+			WARN_ON(eaten != orig_len);
+			break;
+		}
+
+		/* Positive extra indicates ore bytes than needed for the
+		 * message
+		 */
+
+		WARN_ON(extra > cand_len);
+
+		eaten += (cand_len - extra);
+
+		/* Hurray, we have a new message! */
+		psock->rx_skb_head = NULL;
+
+try_queue:
+		kcm = reserve_rx_kcm(psock, head);
+		if (!kcm) {
+			/* Unable to reserve a KCM, message is held in psock. */
+			break;
+		}
+
+		if (kcm_queue_rcv_skb(&kcm->sk, head)) {
+			/* Should mean socket buffer full */
+			unreserve_rx_kcm(psock, false);
+			goto try_queue;
+		}
+	}
+
+	if (cloned_orig)
+		kfree_skb(orig_skb);
+
+	return eaten;
+}
+
+/* Called with lock held on lower socket */
+static int psock_tcp_read_sock(struct kcm_psock *psock)
+{
+	read_descriptor_t desc;
+
+	desc.arg.data = psock;
+	desc.error = 0;
+	desc.count = 1; /* give more than one skb per call */
+
+	/* sk should be locked here, so okay to do tcp_read_sock */
+	tcp_read_sock(psock->sk, &desc, kcm_tcp_recv);
+
+	unreserve_rx_kcm(psock, true);
+
+	return desc.error;
+}
+
+/* Lower sock lock held */
+static void psock_tcp_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 (unlikely(!psock || psock->rx_stopped))
+		goto out;
+
+	if (psock->ready_rx_msg)
+		goto out;
+
+	if (psock_tcp_read_sock(psock) == -ENOMEM)
+		queue_delayed_work(kcm_wq, &psock->rx_delayed_work, 0);
+
+out:
+	read_unlock_bh(&sk->sk_callback_lock);
+}
+
+static void do_psock_rx_work(struct kcm_psock *psock)
+{
+	read_descriptor_t rd_desc;
+	struct sock *csk = psock->sk;
+
+	/* We need the read lock to synchronize with psock_tcp_data_ready. We
+	 * need the socket lock for calling tcp_read_sock.
+	 */
+	lock_sock(csk);
+	read_lock_bh(&csk->sk_callback_lock);
+
+	if (unlikely(csk->sk_user_data != psock))
+		goto out;
+
+	if (unlikely(psock->rx_stopped))
+		goto out;
+
+	if (psock->ready_rx_msg)
+		goto out;
+
+	rd_desc.arg.data = psock;
+
+	if (psock_tcp_read_sock(psock) == -ENOMEM)
+		queue_delayed_work(kcm_wq, &psock->rx_delayed_work, 0);
+
+out:
+	read_unlock_bh(&csk->sk_callback_lock);
+	release_sock(csk);
+}
+
+static void psock_rx_work(struct work_struct *w)
+{
+	do_psock_rx_work(container_of(w, struct kcm_psock, rx_work));
+}
+
+static void psock_rx_delayed_work(struct work_struct *w)
+{
+	do_psock_rx_work(container_of(w, struct kcm_psock,
+				      rx_delayed_work.work));
+}
+
+static void psock_tcp_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);
+}
+
+static void psock_tcp_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)
+		queue_work(kcm_wq, &kcm->tx_work);
+
+	spin_unlock_bh(&mux->lock);
+out:
+	read_unlock_bh(&sk->sk_callback_lock);
+}
+
+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;
+	} 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;
+}
+
+/* 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;
+		queue_work(kcm_wq, &kcm->tx_work);
+	}
+}
+
+/* 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 */
+
+	WARN_ON(kcm->tx_wait);
+
+	kcm->tx_psock = NULL;
+	psock->tx_kcm = NULL;
+
+	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);
+}
+
+/* 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);
+		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;
+				ret = 0;
+
+				goto try_again;
+			}
+
+			sent += ret;
+			frag_offset += 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;
+	} 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;
+}
+
+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->sk_socket->flags)) {
+		clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+		sk->sk_write_space(sk);
+	}
+
+out:
+	release_sock(sk);
+}
+
+static void kcm_push(struct kcm_sock *kcm)
+{
+	if (kcm->tx_wait_more)
+		kcm_write_msgs(kcm);
+}
+
+static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
+{
+	struct sock *sk = sock->sk;
+	struct kcm_sock *kcm = kcm_sk(sk);
+	struct sk_buff *skb = NULL, *head = NULL;
+	size_t copy, copied = 0;
+	long timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
+	int eor = (sock->type == SOCK_DGRAM) ?
+		  !(msg->msg_flags & MSG_MORE) : !!(msg->msg_flags & MSG_EOR);
+	int err = -EPIPE;
+
+	lock_sock(sk);
+
+	/* Per tcp_sendmsg this should be in poll */
+	sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
+
+	if (sk->sk_err)
+		goto out_error;
+
+	if (kcm->seq_skb) {
+		/* Previously opened message */
+		head = kcm->seq_skb;
+		skb = kcm_tx_msg(head)->last_skb;
+		goto start;
+	}
+
+	/* Call the sk_stream functions to manage the sndbuf mem. */
+	if (!sk_stream_memory_free(sk)) {
+		kcm_push(kcm);
+		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+		err = sk_stream_wait_memory(sk, &timeo);
+		if (err)
+			goto out_error;
+	}
+
+	/* New message, alloc head skb */
+	head = alloc_skb(0, sk->sk_allocation);
+	while (!head) {
+		kcm_push(kcm);
+		err = sk_stream_wait_memory(sk, &timeo);
+		if (err)
+			goto out_error;
+
+		head = alloc_skb(0, sk->sk_allocation);
+	}
+
+	skb = head;
+
+	/* Set ip_summed to CHECKSUM_UNNECESSARY to avoid calling
+	 * csum_and_copy_from_iter from skb_do_copy_data_nocache.
+	 */
+	skb->ip_summed = CHECKSUM_UNNECESSARY;
+
+start:
+	while (msg_data_left(msg)) {
+		bool merge = true;
+		int i = skb_shinfo(skb)->nr_frags;
+		struct page_frag *pfrag = sk_page_frag(sk);
+
+		if (!sk_page_frag_refill(sk, pfrag))
+			goto wait_for_memory;
+
+		if (!skb_can_coalesce(skb, i, pfrag->page,
+				      pfrag->offset)) {
+			if (i == MAX_SKB_FRAGS) {
+				struct sk_buff *tskb;
+
+				tskb = alloc_skb(0, sk->sk_allocation);
+				if (!tskb)
+					goto wait_for_memory;
+
+				if (head == skb)
+					skb_shinfo(head)->frag_list = tskb;
+				else
+					skb->next = tskb;
+
+				skb = tskb;
+				skb->ip_summed = CHECKSUM_UNNECESSARY;
+				continue;
+			}
+			merge = false;
+		}
+
+		copy = min_t(int, msg_data_left(msg),
+			     pfrag->size - pfrag->offset);
+
+		if (!sk_wmem_schedule(sk, copy))
+			goto wait_for_memory;
+
+		err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb,
+					       pfrag->page,
+					       pfrag->offset,
+					       copy);
+		if (err)
+			goto out_error;
+
+		/* Update the skb. */
+		if (merge) {
+			skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
+		} else {
+			skb_fill_page_desc(skb, i, pfrag->page,
+					   pfrag->offset, copy);
+			get_page(pfrag->page);
+		}
+
+		pfrag->offset += copy;
+		copied += copy;
+		if (head != skb) {
+			head->len += copy;
+			head->data_len += copy;
+		}
+
+		continue;
+
+wait_for_memory:
+		kcm_push(kcm);
+		err = sk_stream_wait_memory(sk, &timeo);
+		if (err)
+			goto out_error;
+	}
+
+	if (eor) {
+		bool not_busy = skb_queue_empty(&sk->sk_write_queue);
+
+		/* Message complete, queue it on send buffer */
+		__skb_queue_tail(&sk->sk_write_queue, head);
+		kcm->seq_skb = NULL;
+
+		if (msg->msg_flags & MSG_BATCH) {
+			kcm->tx_wait_more = true;
+		} else if (kcm->tx_wait_more || not_busy) {
+			err = kcm_write_msgs(kcm);
+			if (err < 0) {
+				/* We got a hard error in write_msgs but have
+				 * already queued this message. Report an error
+				 * in the socket, but don't affect return value
+				 * from sendmsg
+				 */
+				pr_warn("KCM: Hard failure on kcm_write_msgs\n");
+				report_csk_error(&kcm->sk, -err);
+			}
+		}
+	} else {
+		/* Message not complete, save state */
+partial_message:
+		kcm->seq_skb = head;
+		kcm_tx_msg(head)->last_skb = skb;
+	}
+
+	release_sock(sk);
+	return copied;
+
+out_error:
+	kcm_push(kcm);
+
+	if (copied && sock->type == SOCK_SEQPACKET) {
+		/* Wrote some bytes before encountering an
+		 * error, return partial success.
+		 */
+		goto partial_message;
+	}
+
+	if (head != kcm->seq_skb)
+		kfree_skb(head);
+
+	err = sk_stream_error(sk, msg->msg_flags, err);
+
+	/* make sure we wake any epoll edge trigger waiter */
+	if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN))
+		sk->sk_write_space(sk);
+
+	release_sock(sk);
+	return err;
+}
+
+static struct sk_buff *kcm_wait_data(struct sock *sk, int flags,
+				     long timeo, int *err)
+{
+	struct sk_buff *skb;
+
+	while (!(skb = skb_peek(&sk->sk_receive_queue))) {
+		if (sk->sk_err) {
+			*err = sock_error(sk);
+			return NULL;
+		}
+
+		if (sock_flag(sk, SOCK_DONE))
+			return NULL;
+
+		if ((flags & MSG_DONTWAIT) || !timeo) {
+			*err = -EAGAIN;
+			return NULL;
+		}
+
+		sk_wait_data(sk, &timeo, NULL);
+
+		/* Handle signals */
+		if (signal_pending(current)) {
+			*err = sock_intr_errno(timeo);
+			return NULL;
+		}
+	}
+
+	return skb;
+}
+
+static int kcm_recvmsg(struct socket *sock, struct msghdr *msg,
+		       size_t len, int flags)
+{
+	struct sock *sk = sock->sk;
+	int err = 0;
+	long timeo;
+	struct kcm_rx_msg *rxm;
+	int copied = 0;
+	struct sk_buff *skb;
+
+	timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
+
+	lock_sock(sk);
+
+	skb = kcm_wait_data(sk, flags, timeo, &err);
+	if (!skb)
+		goto out;
+
+	/* Okay, have a message on the receive queue */
+
+	rxm = kcm_rx_msg(skb);
+
+	if (len > rxm->full_len)
+		len = rxm->full_len;
+
+	err = skb_copy_datagram_msg(skb, rxm->offset, msg, len);
+	if (err < 0)
+		goto out;
+
+	copied = len;
+	if (likely(!(flags & MSG_PEEK))) {
+		if (copied < rxm->full_len) {
+			if (sock->type == SOCK_DGRAM) {
+				/* Truncated message */
+				msg->msg_flags |= MSG_TRUNC;
+				goto msg_finished;
+			}
+			rxm->offset += copied;
+			rxm->full_len -= copied;
+		} else {
+msg_finished:
+			/* Finished with message */
+			msg->msg_flags |= MSG_EOR;
+			skb_unlink(skb, &sk->sk_receive_queue);
+			kfree_skb(skb);
+		}
+	}
+
+out:
+	release_sock(sk);
+
+	return copied ? : err;
+}
+
+/* kcm sock lock held */
+static void kcm_recv_disable(struct kcm_sock *kcm)
+{
+	struct kcm_mux *mux = kcm->mux;
+
+	if (kcm->rx_disabled)
+		return;
+
+	spin_lock_bh(&mux->rx_lock);
+
+	kcm->rx_disabled = 1;
+
+	/* If a psock is reserved we'll do cleanup in unreserve */
+	if (!kcm->rx_psock) {
+		if (kcm->rx_wait) {
+			list_del(&kcm->wait_rx_list);
+			kcm->rx_wait = false;
+		}
+
+		requeue_rx_msgs(mux, &kcm->sk.sk_receive_queue);
+	}
+
+	spin_unlock_bh(&mux->rx_lock);
+}
+
+/* kcm sock lock held */
+static void kcm_recv_enable(struct kcm_sock *kcm)
+{
+	struct kcm_mux *mux = kcm->mux;
+
+	if (!kcm->rx_disabled)
+		return;
+
+	spin_lock_bh(&mux->rx_lock);
+
+	kcm->rx_disabled = 0;
+	kcm_rcv_ready(kcm);
+
+	spin_unlock_bh(&mux->rx_lock);
+}
+
+static int kcm_setsockopt(struct socket *sock, int level, int optname,
+			  char __user *optval, unsigned int optlen)
+{
+	struct kcm_sock *kcm = kcm_sk(sock->sk);
+	int val, valbool;
+	int err = 0;
+
+	if (level != SOL_KCM)
+		return -ENOPROTOOPT;
+
+	if (optlen < sizeof(int))
+		return -EINVAL;
+
+	if (get_user(val, (int __user *)optval))
+		return -EINVAL;
+
+	valbool = val ? 1 : 0;
+
+	switch (optname) {
+	case KCM_RECV_DISABLE:
+		lock_sock(&kcm->sk);
+		if (valbool)
+			kcm_recv_disable(kcm);
+		else
+			kcm_recv_enable(kcm);
+		release_sock(&kcm->sk);
+		break;
+	default:
+		err = -ENOPROTOOPT;
+	}
+
+	return err;
+}
+
+static int kcm_getsockopt(struct socket *sock, int level, int optname,
+			  char __user *optval, int __user *optlen)
+{
+	struct kcm_sock *kcm = kcm_sk(sock->sk);
+	int val, len;
+
+	if (level != SOL_KCM)
+		return -ENOPROTOOPT;
+
+	if (get_user(len, optlen))
+		return -EFAULT;
+
+	len = min_t(unsigned int, len, sizeof(int));
+	if (len < 0)
+		return -EINVAL;
+
+	switch (optname) {
+	case KCM_RECV_DISABLE:
+		val = kcm->rx_disabled;
+		break;
+	default:
+		return -ENOPROTOOPT;
+	}
+
+	if (put_user(len, optlen))
+		return -EFAULT;
+	if (copy_to_user(optval, &val, len))
+		return -EFAULT;
+	return 0;
+}
+
+static void init_kcm_sock(struct kcm_sock *kcm, struct kcm_mux *mux)
+{
+	struct kcm_sock *tkcm;
+	struct list_head *head;
+	int index = 0;
+
+	/* For SOCK_SEQPACKET sock type, datagram_poll checks the sk_state, so
+	 * we set sk_state, otherwise epoll_wait always returns right away with
+	 * POLLHUP
+	 */
+	kcm->sk.sk_state = TCP_ESTABLISHED;
+
+	/* Add to mux's kcm sockets list */
+	kcm->mux = mux;
+	spin_lock_bh(&mux->lock);
+
+	head = &mux->kcm_socks;
+	list_for_each_entry(tkcm, &mux->kcm_socks, kcm_sock_list) {
+		if (tkcm->index != index)
+			break;
+		head = &tkcm->kcm_sock_list;
+		index++;
+	}
+
+	list_add(&kcm->kcm_sock_list, head);
+	kcm->index = index;
+
+	mux->kcm_socks_cnt++;
+	spin_unlock_bh(&mux->lock);
+
+	INIT_WORK(&kcm->tx_work, kcm_tx_work);
+
+	spin_lock_bh(&mux->rx_lock);
+	kcm_rcv_ready(kcm);
+	spin_unlock_bh(&mux->rx_lock);
+}
+
+static int kcm_attach(struct socket *sock, struct socket *csock,
+		      struct bpf_prog *prog)
+{
+	struct kcm_sock *kcm = kcm_sk(sock->sk);
+	struct kcm_mux *mux = kcm->mux;
+	struct sock *csk;
+	struct kcm_psock *psock = NULL, *tpsock;
+	struct list_head *head;
+	int index = 0;
+
+	if (csock->ops->family != PF_INET &&
+	    csock->ops->family != PF_INET6)
+		return -EINVAL;
+
+	csk = csock->sk;
+	if (!csk)
+		return -EINVAL;
+
+	/* Only support TCP for now */
+	if (csk->sk_protocol != IPPROTO_TCP)
+		return -EINVAL;
+
+	psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
+	if (!psock)
+		return -ENOMEM;
+
+	psock->mux = mux;
+	psock->sk = csk;
+	psock->bpf_prog = prog;
+	INIT_WORK(&psock->rx_work, psock_rx_work);
+	INIT_DELAYED_WORK(&psock->rx_delayed_work, psock_rx_delayed_work);
+
+	sock_hold(csk);
+
+	write_lock_bh(&csk->sk_callback_lock);
+	psock->save_data_ready = csk->sk_data_ready;
+	psock->save_write_space = csk->sk_write_space;
+	psock->save_state_change = csk->sk_state_change;
+	csk->sk_user_data = psock;
+	csk->sk_data_ready = psock_tcp_data_ready;
+	csk->sk_write_space = psock_tcp_write_space;
+	csk->sk_state_change = psock_tcp_state_change;
+	write_unlock_bh(&csk->sk_callback_lock);
+
+	/* Finished initialization, now add the psock to the MUX. */
+	spin_lock_bh(&mux->lock);
+	head = &mux->psocks;
+	list_for_each_entry(tpsock, &mux->psocks, psock_list) {
+		if (tpsock->index != index)
+			break;
+		head = &tpsock->psock_list;
+		index++;
+	}
+
+	list_add(&psock->psock_list, head);
+	psock->index = index;
+
+	mux->psocks_cnt++;
+	psock_now_avail(psock);
+	spin_unlock_bh(&mux->lock);
+
+	/* Schedule RX work in case there are already bytes queued */
+	queue_work(kcm_wq, &psock->rx_work);
+
+	return 0;
+}
+
+static int kcm_attach_ioctl(struct socket *sock, struct kcm_attach *info)
+{
+	struct socket *csock;
+	struct bpf_prog *prog;
+	int err;
+
+	csock = sockfd_lookup(info->fd, &err);
+	if (!csock)
+		return -ENOENT;
+
+	prog = bpf_prog_get(info->bpf_fd);
+	if (IS_ERR(prog)) {
+		err = PTR_ERR(prog);
+		goto out;
+	}
+
+	if (prog->type != BPF_PROG_TYPE_SOCKET_FILTER) {
+		bpf_prog_put(prog);
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = kcm_attach(sock, csock, prog);
+	if (err) {
+		bpf_prog_put(prog);
+		goto out;
+	}
+
+	/* Keep reference on file also */
+
+	return 0;
+out:
+	fput(csock->file);
+	return err;
+}
+
+static void kcm_unattach(struct kcm_psock *psock)
+{
+	struct sock *csk = psock->sk;
+	struct kcm_mux *mux = psock->mux;
+
+	/* Stop getting callbacks from TCP socket. After this there should
+	 * be no way to reserve a kcm for this psock.
+	 */
+	write_lock_bh(&csk->sk_callback_lock);
+	csk->sk_user_data = NULL;
+	csk->sk_data_ready = psock->save_data_ready;
+	csk->sk_write_space = psock->save_write_space;
+	csk->sk_state_change = psock->save_state_change;
+	psock->rx_stopped = 1;
+
+	if (WARN_ON(psock->rx_kcm)) {
+		write_unlock_bh(&csk->sk_callback_lock);
+		return;
+	}
+
+	spin_lock_bh(&mux->rx_lock);
+
+	/* Stop receiver activities. After this point psock should not be
+	 * able to get onto ready list either through callbacks or work.
+	 */
+	if (psock->ready_rx_msg) {
+		list_del(&psock->psock_ready_list);
+		kfree_skb(psock->ready_rx_msg);
+		psock->ready_rx_msg = NULL;
+	}
+
+	spin_unlock_bh(&mux->rx_lock);
+
+	write_unlock_bh(&csk->sk_callback_lock);
+
+	cancel_work_sync(&psock->rx_work);
+	cancel_delayed_work_sync(&psock->rx_delayed_work);
+
+	bpf_prog_put(psock->bpf_prog);
+
+	kfree_skb(psock->rx_skb_head);
+	psock->rx_skb_head = NULL;
+
+	spin_lock_bh(&mux->lock);
+
+	if (psock->tx_kcm) {
+		/* psock was reserved.  Just mark it finished and we will clean
+		 * up in the kcm paths, we need kcm lock which can not be
+		 * acquired here.
+		 */
+		spin_unlock_bh(&mux->lock);
+
+		/* We are unattaching a socket that is reserved. Abort the
+		 * socket since we may be out of sync in sending on it. We need
+		 * to do this without the mux lock.
+		 */
+		kcm_abort_tx_psock(psock, EPIPE, false);
+
+		spin_lock_bh(&mux->lock);
+		if (!psock->tx_kcm) {
+			/* psock now unreserved in window mux was unlocked */
+			goto no_reserved;
+		}
+		psock->done = 1;
+
+		/* Commit done before queuing work to process it */
+		smp_mb();
+
+		/* Queue tx work to make sure psock->done is handled */
+		queue_work(kcm_wq, &psock->tx_kcm->tx_work);
+		spin_unlock_bh(&mux->lock);
+	} else {
+no_reserved:
+		if (!psock->tx_stopped)
+			list_del(&psock->psock_avail_list);
+		list_del(&psock->psock_list);
+		mux->psocks_cnt--;
+		spin_unlock_bh(&mux->lock);
+
+		sock_put(csk);
+		fput(csk->sk_socket->file);
+		kmem_cache_free(kcm_psockp, psock);
+	}
+}
+
+static int kcm_unattach_ioctl(struct socket *sock, struct kcm_unattach *info)
+{
+	struct kcm_sock *kcm = kcm_sk(sock->sk);
+	struct kcm_mux *mux = kcm->mux;
+	struct kcm_psock *psock;
+	struct socket *csock;
+	struct sock *csk;
+	int err;
+
+	csock = sockfd_lookup(info->fd, &err);
+	if (!csock)
+		return -ENOENT;
+
+	csk = csock->sk;
+	if (!csk) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = -ENOENT;
+
+	spin_lock_bh(&mux->lock);
+
+	list_for_each_entry(psock, &mux->psocks, psock_list) {
+		if (psock->sk != csk)
+			continue;
+
+		/* Found the matching psock */
+
+		if (psock->unattaching || WARN_ON(psock->done)) {
+			err = -EALREADY;
+			break;
+		}
+
+		psock->unattaching = 1;
+
+		spin_unlock_bh(&mux->lock);
+
+		kcm_unattach(psock);
+
+		err = 0;
+		goto out;
+	}
+
+	spin_unlock_bh(&mux->lock);
+
+out:
+	fput(csock->file);
+	return err;
+}
+
+static struct proto kcm_proto = {
+	.name	= "KCM",
+	.owner	= THIS_MODULE,
+	.obj_size = sizeof(struct kcm_sock),
+};
+
+/* Clone a kcm socket. */
+static int kcm_clone(struct socket *osock, struct kcm_clone *info,
+		     struct socket **newsockp)
+{
+	struct socket *newsock;
+	struct sock *newsk;
+	struct file *newfile;
+	int err, newfd;
+
+	err = -ENFILE;
+	newsock = sock_alloc();
+	if (!newsock)
+		goto out;
+
+	newsock->type = osock->type;
+	newsock->ops = osock->ops;
+
+	__module_get(newsock->ops->owner);
+
+	newfd = get_unused_fd_flags(0);
+	if (unlikely(newfd < 0)) {
+		err = newfd;
+		goto out_fd_fail;
+	}
+
+	newfile = sock_alloc_file(newsock, 0, osock->sk->sk_prot_creator->name);
+	if (unlikely(IS_ERR(newfile))) {
+		err = PTR_ERR(newfile);
+		goto out_sock_alloc_fail;
+	}
+
+	newsk = sk_alloc(sock_net(osock->sk), PF_KCM, GFP_KERNEL,
+			 &kcm_proto, true);
+	if (!newsk) {
+		err = -ENOMEM;
+		goto out_sk_alloc_fail;
+	}
+
+	sock_init_data(newsock, newsk);
+	init_kcm_sock(kcm_sk(newsk), kcm_sk(osock->sk)->mux);
+
+	fd_install(newfd, newfile);
+	*newsockp = newsock;
+	info->fd = newfd;
+
+	return 0;
+
+out_sk_alloc_fail:
+	fput(newfile);
+out_sock_alloc_fail:
+	put_unused_fd(newfd);
+out_fd_fail:
+	sock_release(newsock);
+out:
+	return err;
+}
+
+static int kcm_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
+{
+	int err;
+
+	switch (cmd) {
+	case SIOCKCMATTACH: {
+		struct kcm_attach info;
+
+		if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
+			err = -EFAULT;
+
+		err = kcm_attach_ioctl(sock, &info);
+
+		break;
+	}
+	case SIOCKCMUNATTACH: {
+		struct kcm_unattach info;
+
+		if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
+			err = -EFAULT;
+
+		err = kcm_unattach_ioctl(sock, &info);
+
+		break;
+	}
+	case SIOCKCMCLONE: {
+		struct kcm_clone info;
+		struct socket *newsock = NULL;
+
+		if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
+			err = -EFAULT;
+
+		err = kcm_clone(sock, &info, &newsock);
+
+		if (!err) {
+			if (copy_to_user((void __user *)arg, &info,
+					 sizeof(info))) {
+				err = -EFAULT;
+				sock_release(newsock);
+			}
+		}
+
+		break;
+	}
+	default:
+		err = -ENOIOCTLCMD;
+		break;
+	}
+
+	return err;
+}
+
+static void free_mux(struct rcu_head *rcu)
+{
+	struct kcm_mux *mux = container_of(rcu,
+	    struct kcm_mux, rcu);
+
+	kmem_cache_free(kcm_muxp, mux);
+}
+
+static void release_mux(struct kcm_mux *mux)
+{
+	struct kcm_net *knet = mux->knet;
+	struct kcm_psock *psock, *tmp_psock;
+
+	/* Release psocks */
+	list_for_each_entry_safe(psock, tmp_psock,
+				 &mux->psocks, psock_list) {
+		if (!WARN_ON(psock->unattaching))
+			kcm_unattach(psock);
+	}
+
+	if (WARN_ON(mux->psocks_cnt))
+		return;
+
+	__skb_queue_purge(&mux->rx_hold_queue);
+
+	mutex_lock(&knet->mutex);
+	list_del_rcu(&mux->kcm_mux_list);
+	knet->count--;
+	mutex_unlock(&knet->mutex);
+
+	call_rcu(&mux->rcu, free_mux);
+}
+
+static void kcm_done(struct kcm_sock *kcm)
+{
+	struct kcm_mux *mux = kcm->mux;
+	struct sock *sk = &kcm->sk;
+	int socks_cnt;
+
+	spin_lock_bh(&mux->rx_lock);
+	if (kcm->rx_psock) {
+		/* Cleanup in unreserve_rx_kcm */
+		WARN_ON(kcm->done);
+		kcm->rx_disabled = 1;
+		kcm->done = 1;
+		spin_unlock_bh(&mux->rx_lock);
+		return;
+	}
+
+	if (kcm->rx_wait) {
+		list_del(&kcm->wait_rx_list);
+		kcm->rx_wait = false;
+	}
+	/* Move any pending receive messages to other kcm sockets */
+	requeue_rx_msgs(mux, &sk->sk_receive_queue);
+
+	spin_unlock_bh(&mux->rx_lock);
+
+	if (WARN_ON(sk_rmem_alloc_get(sk)))
+		return;
+
+	/* Detach from MUX */
+	spin_lock_bh(&mux->lock);
+
+	list_del(&kcm->kcm_sock_list);
+	mux->kcm_socks_cnt--;
+	socks_cnt = mux->kcm_socks_cnt;
+
+	spin_unlock_bh(&mux->lock);
+
+	if (!socks_cnt) {
+		/* We are done with the mux now. */
+		release_mux(mux);
+	}
+
+	WARN_ON(kcm->rx_wait);
+
+	sock_put(&kcm->sk);
+}
+
+/* Called by kcm_release to close a KCM socket.
+ * If this is the last KCM socket on the MUX, destroy the MUX.
+ */
+static int kcm_release(struct socket *sock)
+{
+	struct sock *sk = sock->sk;
+	struct kcm_sock *kcm;
+	struct kcm_mux *mux;
+	struct kcm_psock *psock;
+
+	if (!sk)
+		return 0;
+
+	kcm = kcm_sk(sk);
+	mux = kcm->mux;
+
+	sock_orphan(sk);
+	kfree_skb(kcm->seq_skb);
+
+	lock_sock(sk);
+	/* Purge queue under lock to avoid race condition with tx_work trying
+	 * to act when queue is nonempty. If tx_work runs after this point
+	 * it will just return.
+	 */
+	__skb_queue_purge(&sk->sk_write_queue);
+	release_sock(sk);
+
+	spin_lock_bh(&mux->lock);
+	if (kcm->tx_wait) {
+		/* Take of tx_wait list, after this point there should be no way
+		 * that a psock will be assigned to this kcm.
+		 */
+		list_del(&kcm->wait_psock_list);
+		kcm->tx_wait = false;
+	}
+	spin_unlock_bh(&mux->lock);
+
+	/* Cancel work. After this point there should be no outside references
+	 * to the kcm socket.
+	 */
+	cancel_work_sync(&kcm->tx_work);
+
+	lock_sock(sk);
+	psock = kcm->tx_psock;
+	if (psock) {
+		/* A psock was reserved, so we need to kill it since it
+		 * may already have some bytes queued from a message. We
+		 * need to do this after removing kcm from tx_wait list.
+		 */
+		kcm_abort_tx_psock(psock, EPIPE, false);
+		unreserve_psock(kcm);
+	}
+	release_sock(sk);
+
+	WARN_ON(kcm->tx_wait);
+	WARN_ON(kcm->tx_psock);
+
+	sock->sk = NULL;
+
+	kcm_done(kcm);
+
+	return 0;
+}
+
+static const struct proto_ops kcm_ops = {
+	.family =	PF_KCM,
+	.owner =	THIS_MODULE,
+	.release =	kcm_release,
+	.bind =		sock_no_bind,
+	.connect =	sock_no_connect,
+	.socketpair =	sock_no_socketpair,
+	.accept =	sock_no_accept,
+	.getname =	sock_no_getname,
+	.poll =		datagram_poll,
+	.ioctl =	kcm_ioctl,
+	.listen =	sock_no_listen,
+	.shutdown =	sock_no_shutdown,
+	.setsockopt =	kcm_setsockopt,
+	.getsockopt =	kcm_getsockopt,
+	.sendmsg =	kcm_sendmsg,
+	.recvmsg =	kcm_recvmsg,
+	.mmap =		sock_no_mmap,
+	.sendpage =	sock_no_sendpage,
+};
+
+/* Create proto operation for kcm sockets */
+static int kcm_create(struct net *net, struct socket *sock,
+		      int protocol, int kern)
+{
+	struct kcm_net *knet = net_generic(net, kcm_net_id);
+	struct sock *sk;
+	struct kcm_mux *mux;
+
+	switch (sock->type) {
+	case SOCK_DGRAM:
+	case SOCK_SEQPACKET:
+		sock->ops = &kcm_ops;
+		break;
+	default:
+		return -ESOCKTNOSUPPORT;
+	}
+
+	if (protocol != KCMPROTO_CONNECTED)
+		return -EPROTONOSUPPORT;
+
+	sk = sk_alloc(net, PF_KCM, GFP_KERNEL, &kcm_proto, kern);
+	if (!sk)
+		return -ENOMEM;
+
+	/* Allocate a kcm mux, shared between KCM sockets */
+	mux = kmem_cache_zalloc(kcm_muxp, GFP_KERNEL);
+	if (!mux) {
+		sk_free(sk);
+		return -ENOMEM;
+	}
+
+	spin_lock_init(&mux->lock);
+	spin_lock_init(&mux->rx_lock);
+	INIT_LIST_HEAD(&mux->kcm_socks);
+	INIT_LIST_HEAD(&mux->kcm_rx_waiters);
+	INIT_LIST_HEAD(&mux->kcm_tx_waiters);
+
+	INIT_LIST_HEAD(&mux->psocks);
+	INIT_LIST_HEAD(&mux->psocks_ready);
+	INIT_LIST_HEAD(&mux->psocks_avail);
+
+	mux->knet = knet;
+
+	/* Add new MUX to list */
+	mutex_lock(&knet->mutex);
+	list_add_rcu(&mux->kcm_mux_list, &knet->mux_list);
+	knet->count++;
+	mutex_unlock(&knet->mutex);
+
+	skb_queue_head_init(&mux->rx_hold_queue);
+
+	/* Init KCM socket */
+	sock_init_data(sock, sk);
+	init_kcm_sock(kcm_sk(sk), mux);
+
+	return 0;
+}
+
+static struct net_proto_family kcm_family_ops = {
+	.family = PF_KCM,
+	.create = kcm_create,
+	.owner  = THIS_MODULE,
+};
+
+static __net_init int kcm_init_net(struct net *net)
+{
+	struct kcm_net *knet = net_generic(net, kcm_net_id);
+
+	INIT_LIST_HEAD_RCU(&knet->mux_list);
+	mutex_init(&knet->mutex);
+
+	return 0;
+}
+
+static __net_exit void kcm_exit_net(struct net *net)
+{
+	struct kcm_net *knet = net_generic(net, kcm_net_id);
+
+	/* All KCM sockets should be closed at this point, which should mean
+	 * that all multiplexors and psocks have been destroyed.
+	 */
+	WARN_ON(!list_empty(&knet->mux_list));
+}
+
+static struct pernet_operations kcm_net_ops = {
+	.init = kcm_init_net,
+	.exit = kcm_exit_net,
+	.id   = &kcm_net_id,
+	.size = sizeof(struct kcm_net),
+};
+
+static int __init kcm_init(void)
+{
+	int err = -ENOMEM;
+
+	kcm_muxp = kmem_cache_create("kcm_mux_cache",
+				     sizeof(struct kcm_mux), 0,
+				     SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
+	if (!kcm_muxp)
+		goto fail;
+
+	kcm_psockp = kmem_cache_create("kcm_psock_cache",
+				       sizeof(struct kcm_psock), 0,
+					SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
+	if (!kcm_psockp)
+		goto fail;
+
+	kcm_wq = create_singlethread_workqueue("kkcmd");
+	if (!kcm_wq)
+		goto fail;
+
+	err = proto_register(&kcm_proto, 1);
+	if (err)
+		goto fail;
+
+	err = sock_register(&kcm_family_ops);
+	if (err)
+		goto sock_register_fail;
+
+	err = register_pernet_device(&kcm_net_ops);
+	if (err)
+		goto net_ops_fail;
+
+	return 0;
+
+net_ops_fail:
+	sock_unregister(PF_KCM);
+
+sock_register_fail:
+	proto_unregister(&kcm_proto);
+
+fail:
+	kmem_cache_destroy(kcm_muxp);
+	kmem_cache_destroy(kcm_psockp);
+
+	if (kcm_wq)
+		destroy_workqueue(kcm_wq);
+
+	return err;
+}
+
+static void __exit kcm_exit(void)
+{
+	unregister_pernet_device(&kcm_net_ops);
+	sock_unregister(PF_KCM);
+	proto_unregister(&kcm_proto);
+	destroy_workqueue(kcm_wq);
+
+	kmem_cache_destroy(kcm_muxp);
+	kmem_cache_destroy(kcm_psockp);
+}
+
+module_init(kcm_init);
+module_exit(kcm_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_NETPROTO(PF_KCM);
+