fs/lockd/svc.c

root/fs/lockd/svc.c
// SPDX-License-Identifier: GPL-2.0-only
/*
 * linux/fs/lockd/svc.c
 *
 * This is the central lockd service.
 *
 * FIXME: Separate the lockd NFS server functionality from the lockd NFS
 *        client functionality. Oh why didn't Sun create two separate
 *        services in the first place?
 *
 * Authors:     Olaf Kirch (okir@monad.swb.de)
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/moduleparam.h>

#include <linux/sched/signal.h>
#include <linux/errno.h>
#include <linux/in.h>
#include <linux/uio.h>
#include <linux/smp.h>
#include <linux/mutex.h>
#include <linux/freezer.h>
#include <linux/inetdevice.h>

#include <linux/sunrpc/types.h>
#include <linux/sunrpc/stats.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/svc.h>
#include <linux/sunrpc/svcsock.h>
#include <linux/sunrpc/svc_xprt.h>
#include <net/ip.h>
#include <net/addrconf.h>
#include <net/ipv6.h>
#include <linux/lockd/lockd.h>
#include <linux/nfs.h>

#include "netns.h"
#include "procfs.h"
#include "netlink.h"

#define NLMDBG_FACILITY         NLMDBG_SVC
#define LOCKD_BUFSIZE           (1024 + NLMSVC_XDRSIZE)

static struct svc_program       nlmsvc_program;

const struct nlmsvc_binding     *nlmsvc_ops;
EXPORT_SYMBOL_GPL(nlmsvc_ops);

static DEFINE_MUTEX(nlmsvc_mutex);
static unsigned int             nlmsvc_users;
static struct svc_serv          *nlmsvc_serv;

static void nlmsvc_request_retry(struct timer_list *tl)
{
        svc_wake_up(nlmsvc_serv);
}
DEFINE_TIMER(nlmsvc_retry, nlmsvc_request_retry);

unsigned int lockd_net_id;

/*
 * These can be set at insmod time (useful for NFS as root filesystem),
 * and also changed through the sysctl interface.  -- Jamie Lokier, Aug 2003
 */
static unsigned long            nlm_grace_period;
unsigned long                   nlm_timeout = LOCKD_DFLT_TIMEO;
static int                      nlm_udpport, nlm_tcpport;

/*
 * Constants needed for the sysctl interface.
 */
static const unsigned long      nlm_grace_period_min = 0;
static const unsigned long      nlm_grace_period_max = 240;
static const unsigned long      nlm_timeout_min = 3;
static const unsigned long      nlm_timeout_max = 20;

#ifdef CONFIG_SYSCTL
static const int                nlm_port_min = 0, nlm_port_max = 65535;
static struct ctl_table_header * nlm_sysctl_table;
#endif

static unsigned long get_lockd_grace_period(struct net *net)
{
        struct lockd_net *ln = net_generic(net, lockd_net_id);

        /* Return the net-ns specific grace period, if there is one */
        if (ln->gracetime)
                return ln->gracetime * HZ;

        /* Note: nlm_timeout should always be nonzero */
        if (nlm_grace_period)
                return roundup(nlm_grace_period, nlm_timeout) * HZ;
        else
                return nlm_timeout * 5 * HZ;
}

static void grace_ender(struct work_struct *grace)
{
        struct delayed_work *dwork = to_delayed_work(grace);
        struct lockd_net *ln = container_of(dwork, struct lockd_net,
                                            grace_period_end);

        locks_end_grace(&ln->lockd_manager);
}

static void set_grace_period(struct net *net)
{
        unsigned long grace_period = get_lockd_grace_period(net);
        struct lockd_net *ln = net_generic(net, lockd_net_id);

        locks_start_grace(net, &ln->lockd_manager);
        cancel_delayed_work_sync(&ln->grace_period_end);
        schedule_delayed_work(&ln->grace_period_end, grace_period);
}

/*
 * This is the lockd kernel thread
 */
static int
lockd(void *vrqstp)
{
        struct svc_rqst *rqstp = vrqstp;
        struct net *net = &init_net;
        struct lockd_net *ln = net_generic(net, lockd_net_id);

        svc_thread_init_status(rqstp, 0);

        /* try_to_freeze() is called from svc_recv() */
        set_freezable();

        dprintk("NFS locking service started (ver " LOCKD_VERSION ").\n");

        /*
         * The main request loop. We don't terminate until the last
         * NFS mount or NFS daemon has gone away.
         */
        while (!svc_thread_should_stop(rqstp)) {
                nlmsvc_retry_blocked(rqstp);
                svc_recv(rqstp, 0);
        }
        if (nlmsvc_ops)
                nlmsvc_invalidate_all();
        nlm_shutdown_hosts();
        cancel_delayed_work_sync(&ln->grace_period_end);
        locks_end_grace(&ln->lockd_manager);

        dprintk("lockd_down: service stopped\n");

        svc_exit_thread(rqstp);
        return 0;
}

static int create_lockd_listener(struct svc_serv *serv, const char *name,
                                 struct net *net, const int family,
                                 const unsigned short port,
                                 const struct cred *cred)
{
        struct svc_xprt *xprt;

        xprt = svc_find_xprt(serv, name, net, family, 0);
        if (xprt == NULL)
                return svc_xprt_create(serv, name, net, family, port,
                                       SVC_SOCK_DEFAULTS, cred);
        svc_xprt_put(xprt);
        return 0;
}

static int create_lockd_family(struct svc_serv *serv, struct net *net,
                               const int family, const struct cred *cred)
{
        struct lockd_net *ln = net_generic(net, lockd_net_id);
        int err;

        err = create_lockd_listener(serv, "udp", net, family,
                                    ln->udp_port ? ln->udp_port : nlm_udpport, cred);
        if (err < 0)
                return err;

        return create_lockd_listener(serv, "tcp", net, family,
                                     ln->tcp_port ? ln->tcp_port : nlm_tcpport, cred);
}

/*
 * Ensure there are active UDP and TCP listeners for lockd.
 *
 * Even if we have only TCP NFS mounts and/or TCP NFSDs, some
 * local services (such as rpc.statd) still require UDP, and
 * some NFS servers do not yet support NLM over TCP.
 *
 * Returns zero if all listeners are available; otherwise a
 * negative errno value is returned.
 */
static int make_socks(struct svc_serv *serv, struct net *net,
                const struct cred *cred)
{
        static int warned;
        int err;

        err = create_lockd_family(serv, net, PF_INET, cred);
        if (err < 0)
                goto out_err;

        err = create_lockd_family(serv, net, PF_INET6, cred);
        if (err < 0 && err != -EAFNOSUPPORT)
                goto out_err;

        warned = 0;
        return 0;

out_err:
        if (warned++ == 0)
                printk(KERN_WARNING
                        "lockd_up: makesock failed, error=%d\n", err);
        svc_xprt_destroy_all(serv, net, true);
        return err;
}

static int lockd_up_net(struct svc_serv *serv, struct net *net,
                const struct cred *cred)
{
        struct lockd_net *ln = net_generic(net, lockd_net_id);
        int error;

        if (ln->nlmsvc_users++)
                return 0;

        error = svc_bind(serv, net);
        if (error)
                goto err_bind;

        error = make_socks(serv, net, cred);
        if (error < 0)
                goto err_bind;
        set_grace_period(net);
        dprintk("%s: per-net data created; net=%x\n", __func__, net->ns.inum);
        return 0;

err_bind:
        ln->nlmsvc_users--;
        return error;
}

static void lockd_down_net(struct svc_serv *serv, struct net *net)
{
        struct lockd_net *ln = net_generic(net, lockd_net_id);

        if (ln->nlmsvc_users) {
                if (--ln->nlmsvc_users == 0) {
                        nlm_shutdown_hosts_net(net);
                        cancel_delayed_work_sync(&ln->grace_period_end);
                        locks_end_grace(&ln->lockd_manager);
                        svc_xprt_destroy_all(serv, net, true);
                }
        } else {
                pr_err("%s: no users! net=%x\n",
                        __func__, net->ns.inum);
                BUG();
        }
}

static int lockd_inetaddr_event(struct notifier_block *this,
        unsigned long event, void *ptr)
{
        struct in_ifaddr *ifa = (struct in_ifaddr *)ptr;
        struct sockaddr_in sin;

        if (event != NETDEV_DOWN)
                goto out;

        if (nlmsvc_serv) {
                dprintk("lockd_inetaddr_event: removed %pI4\n",
                        &ifa->ifa_local);
                sin.sin_family = AF_INET;
                sin.sin_addr.s_addr = ifa->ifa_local;
                svc_age_temp_xprts_now(nlmsvc_serv, (struct sockaddr *)&sin);
        }

out:
        return NOTIFY_DONE;
}

static struct notifier_block lockd_inetaddr_notifier = {
        .notifier_call = lockd_inetaddr_event,
};

#if IS_ENABLED(CONFIG_IPV6)
static int lockd_inet6addr_event(struct notifier_block *this,
        unsigned long event, void *ptr)
{
        struct inet6_ifaddr *ifa = (struct inet6_ifaddr *)ptr;
        struct sockaddr_in6 sin6;

        if (event != NETDEV_DOWN)
                goto out;

        if (nlmsvc_serv) {
                dprintk("lockd_inet6addr_event: removed %pI6\n", &ifa->addr);
                sin6.sin6_family = AF_INET6;
                sin6.sin6_addr = ifa->addr;
                if (ipv6_addr_type(&sin6.sin6_addr) & IPV6_ADDR_LINKLOCAL)
                        sin6.sin6_scope_id = ifa->idev->dev->ifindex;
                svc_age_temp_xprts_now(nlmsvc_serv, (struct sockaddr *)&sin6);
        }

out:
        return NOTIFY_DONE;
}

static struct notifier_block lockd_inet6addr_notifier = {
        .notifier_call = lockd_inet6addr_event,
};
#endif

static int lockd_get(void)
{
        struct svc_serv *serv;
        int error;

        if (nlmsvc_serv) {
                nlmsvc_users++;
                return 0;
        }

        /*
         * Sanity check: if there's no pid,
         * we should be the first user ...
         */
        if (nlmsvc_users)
                printk(KERN_WARNING
                        "lockd_up: no pid, %d users??\n", nlmsvc_users);

        serv = svc_create(&nlmsvc_program, LOCKD_BUFSIZE, lockd);
        if (!serv) {
                printk(KERN_WARNING "lockd_up: create service failed\n");
                return -ENOMEM;
        }

        error = svc_set_num_threads(serv, 0, 1);
        if (error < 0) {
                svc_destroy(&serv);
                return error;
        }

        nlmsvc_serv = serv;
        register_inetaddr_notifier(&lockd_inetaddr_notifier);
#if IS_ENABLED(CONFIG_IPV6)
        register_inet6addr_notifier(&lockd_inet6addr_notifier);
#endif
        dprintk("lockd_up: service created\n");
        nlmsvc_users++;
        return 0;
}

static void lockd_put(void)
{
        if (WARN(nlmsvc_users <= 0, "lockd_down: no users!\n"))
                return;
        if (--nlmsvc_users)
                return;

        unregister_inetaddr_notifier(&lockd_inetaddr_notifier);
#if IS_ENABLED(CONFIG_IPV6)
        unregister_inet6addr_notifier(&lockd_inet6addr_notifier);
#endif

        svc_set_num_threads(nlmsvc_serv, 0, 0);
        timer_delete_sync(&nlmsvc_retry);
        svc_destroy(&nlmsvc_serv);
        dprintk("lockd_down: service destroyed\n");
}

/*
 * Bring up the lockd process if it's not already up.
 */
int lockd_up(struct net *net, const struct cred *cred)
{
        int error;

        mutex_lock(&nlmsvc_mutex);

        error = lockd_get();
        if (error)
                goto err;

        error = lockd_up_net(nlmsvc_serv, net, cred);
        if (error < 0) {
                lockd_put();
                goto err;
        }

err:
        mutex_unlock(&nlmsvc_mutex);
        return error;
}
EXPORT_SYMBOL_GPL(lockd_up);

/*
 * Decrement the user count and bring down lockd if we're the last.
 */
void
lockd_down(struct net *net)
{
        mutex_lock(&nlmsvc_mutex);
        lockd_down_net(nlmsvc_serv, net);
        lockd_put();
        mutex_unlock(&nlmsvc_mutex);
}
EXPORT_SYMBOL_GPL(lockd_down);

#ifdef CONFIG_SYSCTL

/*
 * Sysctl parameters (same as module parameters, different interface).
 */

static const struct ctl_table nlm_sysctls[] = {
        {
                .procname       = "nlm_grace_period",
                .data           = &nlm_grace_period,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
                .extra1         = (unsigned long *) &nlm_grace_period_min,
                .extra2         = (unsigned long *) &nlm_grace_period_max,
        },
        {
                .procname       = "nlm_timeout",
                .data           = &nlm_timeout,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
                .extra1         = (unsigned long *) &nlm_timeout_min,
                .extra2         = (unsigned long *) &nlm_timeout_max,
        },
        {
                .procname       = "nlm_udpport",
                .data           = &nlm_udpport,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = (int *) &nlm_port_min,
                .extra2         = (int *) &nlm_port_max,
        },
        {
                .procname       = "nlm_tcpport",
                .data           = &nlm_tcpport,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = (int *) &nlm_port_min,
                .extra2         = (int *) &nlm_port_max,
        },
        {
                .procname       = "nsm_use_hostnames",
                .data           = &nsm_use_hostnames,
                .maxlen         = sizeof(bool),
                .mode           = 0644,
                .proc_handler   = proc_dobool,
        },
        {
                .procname       = "nsm_local_state",
                .data           = &nsm_local_state,
                .maxlen         = sizeof(nsm_local_state),
                .mode           = 0644,
                .proc_handler   = proc_douintvec,
                .extra1         = SYSCTL_ZERO,
        },
};

#endif  /* CONFIG_SYSCTL */

/*
 * Module (and sysfs) parameters.
 */

#define param_set_min_max(name, type, which_strtol, min, max)           \
static int param_set_##name(const char *val, const struct kernel_param *kp) \
{                                                                       \
        char *endp;                                                     \
        __typeof__(type) num = which_strtol(val, &endp, 0);             \
        if (endp == val || *endp || num < (min) || num > (max))         \
                return -EINVAL;                                         \
        *((type *) kp->arg) = num;                                      \
        return 0;                                                       \
}

static inline int is_callback(u32 proc)
{
        return proc == NLMPROC_GRANTED
                || proc == NLMPROC_GRANTED_MSG
                || proc == NLMPROC_TEST_RES
                || proc == NLMPROC_LOCK_RES
                || proc == NLMPROC_CANCEL_RES
                || proc == NLMPROC_UNLOCK_RES
                || proc == NLMPROC_NSM_NOTIFY;
}


static enum svc_auth_status lockd_authenticate(struct svc_rqst *rqstp)
{
        rqstp->rq_client = NULL;
        switch (rqstp->rq_authop->flavour) {
                case RPC_AUTH_NULL:
                case RPC_AUTH_UNIX:
                        rqstp->rq_auth_stat = rpc_auth_ok;
                        if (rqstp->rq_proc == 0)
                                return SVC_OK;
                        if (is_callback(rqstp->rq_proc)) {
                                /* Leave it to individual procedures to
                                 * call nlmsvc_lookup_host(rqstp)
                                 */
                                return SVC_OK;
                        }
                        return svc_set_client(rqstp);
        }
        rqstp->rq_auth_stat = rpc_autherr_badcred;
        return SVC_DENIED;
}


param_set_min_max(port, int, simple_strtol, 0, 65535)
param_set_min_max(grace_period, unsigned long, simple_strtoul,
                  nlm_grace_period_min, nlm_grace_period_max)
param_set_min_max(timeout, unsigned long, simple_strtoul,
                  nlm_timeout_min, nlm_timeout_max)

MODULE_AUTHOR("Olaf Kirch <okir@monad.swb.de>");
MODULE_DESCRIPTION("NFS file locking service version " LOCKD_VERSION ".");
MODULE_LICENSE("GPL");

module_param_call(nlm_grace_period, param_set_grace_period, param_get_ulong,
                  &nlm_grace_period, 0644);
module_param_call(nlm_timeout, param_set_timeout, param_get_ulong,
                  &nlm_timeout, 0644);
module_param_call(nlm_udpport, param_set_port, param_get_int,
                  &nlm_udpport, 0644);
module_param_call(nlm_tcpport, param_set_port, param_get_int,
                  &nlm_tcpport, 0644);
module_param(nsm_use_hostnames, bool, 0644);

static int lockd_init_net(struct net *net)
{
        struct lockd_net *ln = net_generic(net, lockd_net_id);

        INIT_DELAYED_WORK(&ln->grace_period_end, grace_ender);
        INIT_LIST_HEAD(&ln->lockd_manager.list);
        ln->lockd_manager.block_opens = false;
        INIT_LIST_HEAD(&ln->nsm_handles);
        return 0;
}

static void lockd_exit_net(struct net *net)
{
        struct lockd_net *ln = net_generic(net, lockd_net_id);

        WARN_ONCE(!list_empty(&ln->lockd_manager.list),
                  "net %x %s: lockd_manager.list is not empty\n",
                  net->ns.inum, __func__);
        WARN_ONCE(!list_empty(&ln->nsm_handles),
                  "net %x %s: nsm_handles list is not empty\n",
                  net->ns.inum, __func__);
        WARN_ONCE(delayed_work_pending(&ln->grace_period_end),
                  "net %x %s: grace_period_end was not cancelled\n",
                  net->ns.inum, __func__);
}

static struct pernet_operations lockd_net_ops = {
        .init = lockd_init_net,
        .exit = lockd_exit_net,
        .id = &lockd_net_id,
        .size = sizeof(struct lockd_net),
};


/*
 * Initialising and terminating the module.
 */

static int __init init_nlm(void)
{
        int err;

#ifdef CONFIG_SYSCTL
        err = -ENOMEM;
        nlm_sysctl_table = register_sysctl("fs/nfs", nlm_sysctls);
        if (nlm_sysctl_table == NULL)
                goto err_sysctl;
#endif
        err = register_pernet_subsys(&lockd_net_ops);
        if (err)
                goto err_pernet;

        err = genl_register_family(&lockd_nl_family);
        if (err)
                goto err_netlink;

        err = lockd_create_procfs();
        if (err)
                goto err_procfs;

        return 0;

err_procfs:
        genl_unregister_family(&lockd_nl_family);
err_netlink:
        unregister_pernet_subsys(&lockd_net_ops);
err_pernet:
#ifdef CONFIG_SYSCTL
        unregister_sysctl_table(nlm_sysctl_table);
err_sysctl:
#endif
        return err;
}

static void __exit exit_nlm(void)
{
        /* FIXME: delete all NLM clients */
        nlm_shutdown_hosts();
        genl_unregister_family(&lockd_nl_family);
        lockd_remove_procfs();
        unregister_pernet_subsys(&lockd_net_ops);
#ifdef CONFIG_SYSCTL
        unregister_sysctl_table(nlm_sysctl_table);
#endif
}

module_init(init_nlm);
module_exit(exit_nlm);

/**
 * nlmsvc_dispatch - Process an NLM Request
 * @rqstp: incoming request
 *
 * Return values:
 *  %0: Processing complete; do not send a Reply
 *  %1: Processing complete; send Reply in rqstp->rq_res
 */
static int nlmsvc_dispatch(struct svc_rqst *rqstp)
{
        const struct svc_procedure *procp = rqstp->rq_procinfo;
        __be32 *statp = rqstp->rq_accept_statp;

        if (!procp->pc_decode(rqstp, &rqstp->rq_arg_stream))
                goto out_decode_err;

        *statp = procp->pc_func(rqstp);
        if (*statp == rpc_drop_reply)
                return 0;
        if (*statp != rpc_success)
                return 1;

        if (!procp->pc_encode(rqstp, &rqstp->rq_res_stream))
                goto out_encode_err;

        return 1;

out_decode_err:
        *statp = rpc_garbage_args;
        return 1;

out_encode_err:
        *statp = rpc_system_err;
        return 1;
}

/*
 * Define NLM program and procedures
 */
static DEFINE_PER_CPU_ALIGNED(unsigned long, nlmsvc_version1_count[17]);
static const struct svc_version nlmsvc_version1 = {
        .vs_vers        = 1,
        .vs_nproc       = 17,
        .vs_proc        = nlmsvc_procedures,
        .vs_count       = nlmsvc_version1_count,
        .vs_dispatch    = nlmsvc_dispatch,
        .vs_xdrsize     = NLMSVC_XDRSIZE,
};

static DEFINE_PER_CPU_ALIGNED(unsigned long,
                              nlmsvc_version3_count[ARRAY_SIZE(nlmsvc_procedures)]);
static const struct svc_version nlmsvc_version3 = {
        .vs_vers        = 3,
        .vs_nproc       = ARRAY_SIZE(nlmsvc_procedures),
        .vs_proc        = nlmsvc_procedures,
        .vs_count       = nlmsvc_version3_count,
        .vs_dispatch    = nlmsvc_dispatch,
        .vs_xdrsize     = NLMSVC_XDRSIZE,
};

#ifdef CONFIG_LOCKD_V4
static DEFINE_PER_CPU_ALIGNED(unsigned long,
                              nlmsvc_version4_count[ARRAY_SIZE(nlmsvc_procedures4)]);
static const struct svc_version nlmsvc_version4 = {
        .vs_vers        = 4,
        .vs_nproc       = ARRAY_SIZE(nlmsvc_procedures4),
        .vs_proc        = nlmsvc_procedures4,
        .vs_count       = nlmsvc_version4_count,
        .vs_dispatch    = nlmsvc_dispatch,
        .vs_xdrsize     = NLMSVC_XDRSIZE,
};
#endif

static const struct svc_version *nlmsvc_version[] = {
        [1] = &nlmsvc_version1,
        [3] = &nlmsvc_version3,
#ifdef CONFIG_LOCKD_V4
        [4] = &nlmsvc_version4,
#endif
};

#define NLM_NRVERS      ARRAY_SIZE(nlmsvc_version)
static struct svc_program       nlmsvc_program = {
        .pg_prog                = NLM_PROGRAM,          /* program number */
        .pg_nvers               = NLM_NRVERS,           /* number of entries in nlmsvc_version */
        .pg_vers                = nlmsvc_version,       /* version table */
        .pg_name                = "lockd",              /* service name */
        .pg_class               = "nfsd",               /* share authentication with nfsd */
        .pg_authenticate        = &lockd_authenticate,  /* export authentication */
        .pg_init_request        = svc_generic_init_request,
        .pg_rpcbind_set         = svc_generic_rpcbind_set,
};

/**
 * lockd_nl_server_set_doit - set the lockd server parameters via netlink
 * @skb: reply buffer
 * @info: netlink metadata and command arguments
 *
 * This updates the per-net values. When updating the values in the init_net
 * namespace, also update the "legacy" global values.
 *
 * Return 0 on success or a negative errno.
 */
int lockd_nl_server_set_doit(struct sk_buff *skb, struct genl_info *info)
{
        struct net *net = genl_info_net(info);
        struct lockd_net *ln = net_generic(net, lockd_net_id);
        const struct nlattr *attr;

        if (GENL_REQ_ATTR_CHECK(info, LOCKD_A_SERVER_GRACETIME))
                return -EINVAL;

        if (info->attrs[LOCKD_A_SERVER_GRACETIME] ||
            info->attrs[LOCKD_A_SERVER_TCP_PORT] ||
            info->attrs[LOCKD_A_SERVER_UDP_PORT]) {
                attr = info->attrs[LOCKD_A_SERVER_GRACETIME];
                if (attr) {
                        u32 gracetime = nla_get_u32(attr);

                        if (gracetime > nlm_grace_period_max)
                                return -EINVAL;

                        ln->gracetime = gracetime;

                        if (net == &init_net)
                                nlm_grace_period = gracetime;
                }

                attr = info->attrs[LOCKD_A_SERVER_TCP_PORT];
                if (attr) {
                        ln->tcp_port = nla_get_u16(attr);
                        if (net == &init_net)
                                nlm_tcpport = ln->tcp_port;
                }

                attr = info->attrs[LOCKD_A_SERVER_UDP_PORT];
                if (attr) {
                        ln->udp_port = nla_get_u16(attr);
                        if (net == &init_net)
                                nlm_udpport = ln->udp_port;
                }
        }
        return 0;
}

/**
 * lockd_nl_server_get_doit - get lockd server parameters via netlink
 * @skb: reply buffer
 * @info: netlink metadata and command arguments
 *
 * Return 0 on success or a negative errno.
 */
int lockd_nl_server_get_doit(struct sk_buff *skb, struct genl_info *info)
{
        struct net *net = genl_info_net(info);
        struct lockd_net *ln = net_generic(net, lockd_net_id);
        void *hdr;
        int err;

        skb = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_KERNEL);
        if (!skb)
                return -ENOMEM;

        hdr = genlmsg_iput(skb, info);
        if (!hdr) {
                err = -EMSGSIZE;
                goto err_free_msg;
        }

        err = nla_put_u32(skb, LOCKD_A_SERVER_GRACETIME, ln->gracetime) ||
              nla_put_u16(skb, LOCKD_A_SERVER_TCP_PORT, ln->tcp_port) ||
              nla_put_u16(skb, LOCKD_A_SERVER_UDP_PORT, ln->udp_port);
        if (err)
                goto err_free_msg;

        genlmsg_end(skb, hdr);

        return genlmsg_reply(skb, info);
err_free_msg:
        nlmsg_free(skb);

        return err;
}
Linux
