// 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 *))
{
        int err;
        struct cn_dev *dev = &cdev;

        if (!cn_already_initialized)
                return -EAGAIN;

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

        return 0;
}
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\n");

        spin_lock_bh(&dev->queue_lock);

        list_for_each_entry(cbq, &dev->queue_list, callback_entry) {
                seq_printf(m, "%-15s %u:%u\n",
                           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);