// SPDX-License-Identifier: GPL-2.0-or-later

  /*

   *	connector.c

   *

   * 2004+ Copyright (c) Evgeniy Polyakov <zbr@ioremap.net>

   * All rights reserved.

   */

  #include <linux/compiler.h>

  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/list.h>
  #include <linux/skbuff.h>

  #include <net/netlink.h>

  #include <linux/moduleparam.h>
  #include <linux/connector.h>

  #include <linux/slab.h>

  #include <linux/mutex.h>

  #include <linux/proc_fs.h>
  #include <linux/spinlock.h>

  
  #include <net/sock.h>
  
  MODULE_LICENSE("GPL");

  MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");

  MODULE_DESCRIPTION("Generic userspace <-> kernelspace connector.");

  MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_CONNECTOR);

  static struct cn_dev cdev;

  static int cn_already_initialized;

  
  /*

   * Sends mult (multiple) cn_msg at a time.
   *

   * msg->seq and msg->ack are used to determine message genealogy.
   * When someone sends message it puts there locally unique sequence
   * and random acknowledge numbers.  Sequence number may be copied into
   * nlmsghdr->nlmsg_seq too.
   *
   * Sequence number is incremented with each message to be sent.
   *

   * If we expect a reply to our message then the sequence number in

   * received message MUST be the same as in original message, and
   * acknowledge number MUST be the same + 1.
   *
   * If we receive a message and its sequence number is not equal to the
   * one we are expecting then it is a new message.
   *
   * If we receive a message and its sequence number is the same as one
   * we are expecting but it's acknowledgement number is not equal to
   * the acknowledgement number in the original message + 1, then it is
   * a new message.
   *

   * If msg->len != len, then additional cn_msg messages are expected following
   * the first msg.
   *

   * The message is sent to, the portid if given, the group if given, both if
   * both, or if both are zero then the group is looked up and sent there.

   */

  int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid, u32 __group,

  	gfp_t gfp_mask)

  {
  	struct cn_callback_entry *__cbq;
  	unsigned int size;
  	struct sk_buff *skb;
  	struct nlmsghdr *nlh;
  	struct cn_msg *data;
  	struct cn_dev *dev = &cdev;
  	u32 group = 0;
  	int found = 0;

  	if (portid || __group) {
  		group = __group;
  	} else {

  		spin_lock_bh(&dev->cbdev->queue_lock);
  		list_for_each_entry(__cbq, &dev->cbdev->queue_list,
  				    callback_entry) {

  			if (cn_cb_equal(&__cbq->id.id, &msg->id)) {

  				found = 1;
  				group = __cbq->group;

  				break;

  			}
  		}
  		spin_unlock_bh(&dev->cbdev->queue_lock);
  
  		if (!found)
  			return -ENODEV;

  	}

  	if (!portid && !netlink_has_listeners(dev->nls, group))

  		return -ESRCH;

  	size = sizeof(*msg) + len;

  	skb = nlmsg_new(size, gfp_mask);

  	if (!skb)
  		return -ENOMEM;

  	nlh = nlmsg_put(skb, 0, msg->seq, NLMSG_DONE, size, 0);

  	if (!nlh) {
  		kfree_skb(skb);
  		return -EMSGSIZE;
  	}

  	data = nlmsg_data(nlh);

  	memcpy(data, msg, size);

  
  	NETLINK_CB(skb).dst_group = group;

  	if (group)
  		return netlink_broadcast(dev->nls, skb, portid, group,
  					 gfp_mask);

  	return netlink_unicast(dev->nls, skb, portid,
  			!gfpflags_allow_blocking(gfp_mask));

  }

  EXPORT_SYMBOL_GPL(cn_netlink_send_mult);
  
  /* same as cn_netlink_send_mult except msg->len is used for len */
  int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group,
  	gfp_t gfp_mask)
  {
  	return cn_netlink_send_mult(msg, msg->len, portid, __group, gfp_mask);
  }

  EXPORT_SYMBOL_GPL(cn_netlink_send);

  
  /*
   * Callback helper - queues work and setup destructor for given data.
   */

  static int cn_call_callback(struct sk_buff *skb)

  {

  	struct nlmsghdr *nlh;

  	struct cn_callback_entry *i, *cbq = NULL;

  	struct cn_dev *dev = &cdev;

  	struct cn_msg *msg = nlmsg_data(nlmsg_hdr(skb));

  	struct netlink_skb_parms *nsp = &NETLINK_CB(skb);

  	int err = -ENODEV;

  	/* verify msg->len is within skb */
  	nlh = nlmsg_hdr(skb);
  	if (nlh->nlmsg_len < NLMSG_HDRLEN + sizeof(struct cn_msg) + msg->len)
  		return -EINVAL;

  	spin_lock_bh(&dev->cbdev->queue_lock);

  	list_for_each_entry(i, &dev->cbdev->queue_list, callback_entry) {
  		if (cn_cb_equal(&i->id.id, &msg->id)) {

  			refcount_inc(&i->refcnt);

  			cbq = i;

  			break;
  		}
  	}
  	spin_unlock_bh(&dev->cbdev->queue_lock);

  	if (cbq != NULL) {
  		cbq->callback(msg, nsp);
  		kfree_skb(skb);
  		cn_queue_release_callback(cbq);

  		err = 0;

  	}

  	return err;

  }
  
  /*

   * Main netlink receiving function.
   *

   * It checks skb, netlink header and msg sizes, and calls callback helper.

   */

  static void cn_rx_skb(struct sk_buff *skb)

  {
  	struct nlmsghdr *nlh;

  	int len, err;

  	if (skb->len >= NLMSG_HDRLEN) {

  		nlh = nlmsg_hdr(skb);

  		len = nlmsg_len(nlh);

  		if (len < (int)sizeof(struct cn_msg) ||

  		    skb->len < nlh->nlmsg_len ||

  		    len > CONNECTOR_MAX_MSG_SIZE)

  			return;

  		err = cn_call_callback(skb_get(skb));

  		if (err < 0)
  			kfree_skb(skb);
  	}

  }
  
  /*

   * Callback add routing - adds callback with given ID and name.
   * If there is registered callback with the same ID it will not be added.
   *
   * May sleep.
   */

  int cn_add_callback(struct cb_id *id, const char *name,

  		    void (*callback)(struct cn_msg *,
  				     struct netlink_skb_parms *))

  {

  	struct cn_dev *dev = &cdev;

  	if (!cn_already_initialized)
  		return -EAGAIN;

  	return cn_queue_add_callback(dev->cbdev, name, id, callback);

  }

  EXPORT_SYMBOL_GPL(cn_add_callback);

  
  /*
   * Callback remove routing - removes callback
   * with given ID.
   * If there is no registered callback with given
   * ID nothing happens.
   *
   * May sleep while waiting for reference counter to become zero.
   */
  void cn_del_callback(struct cb_id *id)
  {
  	struct cn_dev *dev = &cdev;
  
  	cn_queue_del_callback(dev->cbdev, id);

  }

  EXPORT_SYMBOL_GPL(cn_del_callback);

  static int __maybe_unused cn_proc_show(struct seq_file *m, void *v)

  {
  	struct cn_queue_dev *dev = cdev.cbdev;
  	struct cn_callback_entry *cbq;
  
  	seq_printf(m, "Name            ID
  ");
  
  	spin_lock_bh(&dev->queue_lock);
  
  	list_for_each_entry(cbq, &dev->queue_list, callback_entry) {
  		seq_printf(m, "%-15s %u:%u
  ",
  			   cbq->id.name,
  			   cbq->id.id.idx,
  			   cbq->id.id.val);
  	}
  
  	spin_unlock_bh(&dev->queue_lock);
  
  	return 0;
  }

  static int cn_init(void)

  {
  	struct cn_dev *dev = &cdev;

  	struct netlink_kernel_cfg cfg = {
  		.groups	= CN_NETLINK_USERS + 0xf,

  		.input	= cn_rx_skb,

  	};

  	dev->nls = netlink_kernel_create(&init_net, NETLINK_CONNECTOR, &cfg);

  	if (!dev->nls)
  		return -EIO;
  
  	dev->cbdev = cn_queue_alloc_dev("cqueue", dev->nls);
  	if (!dev->cbdev) {

  		netlink_kernel_release(dev->nls);

  		return -EINVAL;
  	}

  	cn_already_initialized = 1;

  	proc_create_single("connector", S_IRUGO, init_net.proc_net, cn_proc_show);

  	return 0;
  }

  static void cn_fini(void)

  {
  	struct cn_dev *dev = &cdev;
  
  	cn_already_initialized = 0;

  	remove_proc_entry("connector", init_net.proc_net);

  	cn_queue_free_dev(dev->cbdev);

  	netlink_kernel_release(dev->nls);

  }

  subsys_initcall(cn_init);

  module_exit(cn_fini);