// SPDX-License-Identifier: GPL-2.0
/* Multipath TCP
 *
 * Copyright (c) 2019, Tessares SA.
 */

#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
#endif

#include <net/net_namespace.h>
#include <net/netns/generic.h>

#include "protocol.h"
#include "mib.h"

#define MPTCP_SYSCTL_PATH "net/mptcp"

static int mptcp_pernet_id;

#ifdef CONFIG_SYSCTL
static int mptcp_pm_type_max = __MPTCP_PM_TYPE_MAX;
#endif

struct mptcp_pernet {
#ifdef CONFIG_SYSCTL
        struct ctl_table_header *ctl_table_hdr;
#endif

        unsigned int add_addr_timeout;
        unsigned int blackhole_timeout;
        unsigned int close_timeout;
        unsigned int stale_loss_cnt;
        atomic_t active_disable_times;
        u8 syn_retrans_before_tcp_fallback;
        unsigned long active_disable_stamp;
        u8 mptcp_enabled;
        u8 checksum_enabled;
        u8 allow_join_initial_addr_port;
        u8 pm_type;
        char scheduler[MPTCP_SCHED_NAME_MAX];
        char path_manager[MPTCP_PM_NAME_MAX];
};

static struct mptcp_pernet *mptcp_get_pernet(const struct net *net)
{
        return net_generic(net, mptcp_pernet_id);
}

int mptcp_is_enabled(const struct net *net)
{
        return mptcp_get_pernet(net)->mptcp_enabled;
}

unsigned int mptcp_get_add_addr_timeout(const struct net *net)
{
        return mptcp_get_pernet(net)->add_addr_timeout;
}

int mptcp_is_checksum_enabled(const struct net *net)
{
        return mptcp_get_pernet(net)->checksum_enabled;
}

int mptcp_allow_join_id0(const struct net *net)
{
        return mptcp_get_pernet(net)->allow_join_initial_addr_port;
}

unsigned int mptcp_stale_loss_cnt(const struct net *net)
{
        return mptcp_get_pernet(net)->stale_loss_cnt;
}

unsigned int mptcp_close_timeout(const struct sock *sk)
{
        if (sock_flag(sk, SOCK_DEAD))
                return TCP_TIMEWAIT_LEN;
        return mptcp_get_pernet(sock_net(sk))->close_timeout;
}

int mptcp_get_pm_type(const struct net *net)
{
        return mptcp_get_pernet(net)->pm_type;
}

const char *mptcp_get_path_manager(const struct net *net)
{
        return mptcp_get_pernet(net)->path_manager;
}

const char *mptcp_get_scheduler(const struct net *net)
{
        return mptcp_get_pernet(net)->scheduler;
}

static void mptcp_pernet_set_defaults(struct mptcp_pernet *pernet)
{
        pernet->mptcp_enabled = 1;
        pernet->add_addr_timeout = TCP_RTO_MAX;
        pernet->blackhole_timeout = 3600;
        pernet->syn_retrans_before_tcp_fallback = 2;
        atomic_set(&pernet->active_disable_times, 0);
        pernet->close_timeout = TCP_TIMEWAIT_LEN;
        pernet->checksum_enabled = 0;
        pernet->allow_join_initial_addr_port = 1;
        pernet->stale_loss_cnt = 4;
        pernet->pm_type = MPTCP_PM_TYPE_KERNEL;
        strscpy(pernet->scheduler, "default", sizeof(pernet->scheduler));
        strscpy(pernet->path_manager, "kernel", sizeof(pernet->path_manager));
}

#ifdef CONFIG_SYSCTL
static int mptcp_set_scheduler(char *scheduler, const char *name)
{
        struct mptcp_sched_ops *sched;
        int ret = 0;

        rcu_read_lock();
        sched = mptcp_sched_find(name);
        if (sched)
                strscpy(scheduler, name, MPTCP_SCHED_NAME_MAX);
        else
                ret = -ENOENT;
        rcu_read_unlock();

        return ret;
}

static int proc_scheduler(const struct ctl_table *ctl, int write,
                          void *buffer, size_t *lenp, loff_t *ppos)
{
        char (*scheduler)[MPTCP_SCHED_NAME_MAX] = ctl->data;
        char val[MPTCP_SCHED_NAME_MAX];
        struct ctl_table tbl = {
                .data = val,
                .maxlen = MPTCP_SCHED_NAME_MAX,
        };
        int ret;

        strscpy(val, *scheduler, MPTCP_SCHED_NAME_MAX);

        ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
        if (write && ret == 0)
                ret = mptcp_set_scheduler(*scheduler, val);

        return ret;
}

static int proc_available_schedulers(const struct ctl_table *ctl,
                                     int write, void *buffer,
                                     size_t *lenp, loff_t *ppos)
{
        struct ctl_table tbl = { .maxlen = MPTCP_SCHED_BUF_MAX, };
        int ret;

        tbl.data = kmalloc(tbl.maxlen, GFP_USER);
        if (!tbl.data)
                return -ENOMEM;

        mptcp_get_available_schedulers(tbl.data, MPTCP_SCHED_BUF_MAX);
        ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
        kfree(tbl.data);

        return ret;
}

static int proc_blackhole_detect_timeout(const struct ctl_table *table,
                                         int write, void *buffer, size_t *lenp,
                                         loff_t *ppos)
{
        struct mptcp_pernet *pernet = container_of(table->data,
                                                   struct mptcp_pernet,
                                                   blackhole_timeout);
        int ret;

        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
        if (write && ret == 0)
                atomic_set(&pernet->active_disable_times, 0);

        return ret;
}

static int mptcp_set_path_manager(char *path_manager, const char *name)
{
        struct mptcp_pm_ops *pm_ops;
        int ret = 0;

        rcu_read_lock();
        pm_ops = mptcp_pm_find(name);
        if (pm_ops)
                strscpy(path_manager, name, MPTCP_PM_NAME_MAX);
        else
                ret = -ENOENT;
        rcu_read_unlock();

        return ret;
}

static int proc_path_manager(const struct ctl_table *ctl, int write,
                             void *buffer, size_t *lenp, loff_t *ppos)
{
        struct mptcp_pernet *pernet = container_of(ctl->data,
                                                   struct mptcp_pernet,
                                                   path_manager);
        char (*path_manager)[MPTCP_PM_NAME_MAX] = ctl->data;
        char pm_name[MPTCP_PM_NAME_MAX];
        const struct ctl_table tbl = {
                .data = pm_name,
                .maxlen = MPTCP_PM_NAME_MAX,
        };
        int ret;

        strscpy(pm_name, *path_manager, MPTCP_PM_NAME_MAX);

        ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
        if (write && ret == 0) {
                ret = mptcp_set_path_manager(*path_manager, pm_name);
                if (ret == 0) {
                        u8 pm_type = __MPTCP_PM_TYPE_NR;

                        if (strncmp(pm_name, "kernel", MPTCP_PM_NAME_MAX) == 0)
                                pm_type = MPTCP_PM_TYPE_KERNEL;
                        else if (strncmp(pm_name, "userspace", MPTCP_PM_NAME_MAX) == 0)
                                pm_type = MPTCP_PM_TYPE_USERSPACE;
                        pernet->pm_type = pm_type;
                }
        }

        return ret;
}

static int proc_pm_type(const struct ctl_table *ctl, int write,
                        void *buffer, size_t *lenp, loff_t *ppos)
{
        struct mptcp_pernet *pernet = container_of(ctl->data,
                                                   struct mptcp_pernet,
                                                   pm_type);
        int ret;

        ret = proc_dou8vec_minmax(ctl, write, buffer, lenp, ppos);
        if (write && ret == 0) {
                u8 pm_type = READ_ONCE(*(u8 *)ctl->data);
                char *pm_name = "";

                if (pm_type == MPTCP_PM_TYPE_KERNEL)
                        pm_name = "kernel";
                else if (pm_type == MPTCP_PM_TYPE_USERSPACE)
                        pm_name = "userspace";
                mptcp_set_path_manager(pernet->path_manager, pm_name);
        }

        return ret;
}

static int proc_available_path_managers(const struct ctl_table *ctl,
                                        int write, void *buffer,
                                        size_t *lenp, loff_t *ppos)
{
        struct ctl_table tbl = { .maxlen = MPTCP_PM_BUF_MAX, };
        int ret;

        tbl.data = kmalloc(tbl.maxlen, GFP_USER);
        if (!tbl.data)
                return -ENOMEM;

        mptcp_pm_get_available(tbl.data, MPTCP_PM_BUF_MAX);
        ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
        kfree(tbl.data);

        return ret;
}

static struct ctl_table mptcp_sysctl_table[] = {
        {
                .procname = "enabled",
                .maxlen = sizeof(u8),
                .mode = 0644,
                /* users with CAP_NET_ADMIN or root (not and) can change this
                 * value, same as other sysctl or the 'net' tree.
                 */
                .proc_handler = proc_dou8vec_minmax,
                .extra1       = SYSCTL_ZERO,
                .extra2       = SYSCTL_ONE
        },
        {
                .procname = "add_addr_timeout",
                .maxlen = sizeof(unsigned int),
                .mode = 0644,
                .proc_handler = proc_dointvec_jiffies,
        },
        {
                .procname = "checksum_enabled",
                .maxlen = sizeof(u8),
                .mode = 0644,
                .proc_handler = proc_dou8vec_minmax,
                .extra1       = SYSCTL_ZERO,
                .extra2       = SYSCTL_ONE
        },
        {
                .procname = "allow_join_initial_addr_port",
                .maxlen = sizeof(u8),
                .mode = 0644,
                .proc_handler = proc_dou8vec_minmax,
                .extra1       = SYSCTL_ZERO,
                .extra2       = SYSCTL_ONE
        },
        {
                .procname = "stale_loss_cnt",
                .maxlen = sizeof(unsigned int),
                .mode = 0644,
                .proc_handler = proc_douintvec_minmax,
        },
        {
                .procname = "pm_type",
                .maxlen = sizeof(u8),
                .mode = 0644,
                .proc_handler = proc_pm_type,
                .extra1       = SYSCTL_ZERO,
                .extra2       = &mptcp_pm_type_max
        },
        {
                .procname = "scheduler",
                .maxlen = MPTCP_SCHED_NAME_MAX,
                .mode = 0644,
                .proc_handler = proc_scheduler,
        },
        {
                .procname = "available_schedulers",
                .maxlen = MPTCP_SCHED_BUF_MAX,
                .mode = 0444,
                .proc_handler = proc_available_schedulers,
        },
        {
                .procname = "close_timeout",
                .maxlen = sizeof(unsigned int),
                .mode = 0644,
                .proc_handler = proc_dointvec_jiffies,
        },
        {
                .procname = "blackhole_timeout",
                .maxlen = sizeof(unsigned int),
                .mode = 0644,
                .proc_handler = proc_blackhole_detect_timeout,
                .extra1 = SYSCTL_ZERO,
        },
        {
                .procname = "syn_retrans_before_tcp_fallback",
                .maxlen = sizeof(u8),
                .mode = 0644,
                .proc_handler = proc_dou8vec_minmax,
        },
        {
                .procname = "path_manager",
                .maxlen = MPTCP_PM_NAME_MAX,
                .mode = 0644,
                .proc_handler = proc_path_manager,
        },
        {
                .procname = "available_path_managers",
                .maxlen = MPTCP_PM_BUF_MAX,
                .mode = 0444,
                .proc_handler = proc_available_path_managers,
        },
};

static int mptcp_pernet_new_table(struct net *net, struct mptcp_pernet *pernet)
{
        struct ctl_table_header *hdr;
        struct ctl_table *table;

        table = mptcp_sysctl_table;
        if (!net_eq(net, &init_net)) {
                table = kmemdup(table, sizeof(mptcp_sysctl_table), GFP_KERNEL);
                if (!table)
                        goto err_alloc;
        }

        table[0].data = &pernet->mptcp_enabled;
        table[1].data = &pernet->add_addr_timeout;
        table[2].data = &pernet->checksum_enabled;
        table[3].data = &pernet->allow_join_initial_addr_port;
        table[4].data = &pernet->stale_loss_cnt;
        table[5].data = &pernet->pm_type;
        table[6].data = &pernet->scheduler;
        /* table[7] is for available_schedulers which is read-only info */
        table[8].data = &pernet->close_timeout;
        table[9].data = &pernet->blackhole_timeout;
        table[10].data = &pernet->syn_retrans_before_tcp_fallback;
        table[11].data = &pernet->path_manager;
        /* table[12] is for available_path_managers which is read-only info */

        hdr = register_net_sysctl_sz(net, MPTCP_SYSCTL_PATH, table,
                                     ARRAY_SIZE(mptcp_sysctl_table));
        if (!hdr)
                goto err_reg;

        pernet->ctl_table_hdr = hdr;

        return 0;

err_reg:
        if (!net_eq(net, &init_net))
                kfree(table);
err_alloc:
        return -ENOMEM;
}

static void mptcp_pernet_del_table(struct mptcp_pernet *pernet)
{
        const struct ctl_table *table = pernet->ctl_table_hdr->ctl_table_arg;

        unregister_net_sysctl_table(pernet->ctl_table_hdr);

        kfree(table);
}

#else

static int mptcp_pernet_new_table(struct net *net, struct mptcp_pernet *pernet)
{
        return 0;
}

static void mptcp_pernet_del_table(struct mptcp_pernet *pernet) {}

#endif /* CONFIG_SYSCTL */

/* The following code block is to deal with middle box issues with MPTCP,
 * similar to what is done with TFO.
 * The proposed solution is to disable active MPTCP globally when SYN+MPC are
 * dropped, while SYN without MPC aren't. In this case, active side MPTCP is
 * disabled globally for 1hr at first. Then if it happens again, it is disabled
 * for 2h, then 4h, 8h, ...
 * The timeout is reset back to 1hr when a successful active MPTCP connection is
 * fully established.
 */

/* Disable active MPTCP and record current jiffies and active_disable_times */
void mptcp_active_disable(struct sock *sk)
{
        struct net *net = sock_net(sk);
        struct mptcp_pernet *pernet;

        pernet = mptcp_get_pernet(net);

        if (!READ_ONCE(pernet->blackhole_timeout))
                return;

        /* Paired with READ_ONCE() in mptcp_active_should_disable() */
        WRITE_ONCE(pernet->active_disable_stamp, jiffies);

        /* Paired with smp_rmb() in mptcp_active_should_disable().
         * We want pernet->active_disable_stamp to be updated first.
         */
        smp_mb__before_atomic();
        atomic_inc(&pernet->active_disable_times);

        MPTCP_INC_STATS(net, MPTCP_MIB_BLACKHOLE);
}

/* Calculate timeout for MPTCP active disable
 * Return true if we are still in the active MPTCP disable period
 * Return false if timeout already expired and we should use active MPTCP
 */
bool mptcp_active_should_disable(struct sock *ssk)
{
        struct net *net = sock_net(ssk);
        unsigned int blackhole_timeout;
        struct mptcp_pernet *pernet;
        unsigned long timeout;
        int disable_times;
        int multiplier;

        pernet = mptcp_get_pernet(net);
        blackhole_timeout = READ_ONCE(pernet->blackhole_timeout);

        if (!blackhole_timeout)
                return false;

        disable_times = atomic_read(&pernet->active_disable_times);
        if (!disable_times)
                return false;

        /* Paired with smp_mb__before_atomic() in mptcp_active_disable() */
        smp_rmb();

        /* Limit timeout to max: 2^6 * initial timeout */
        multiplier = 1 << min(disable_times - 1, 6);

        /* Paired with the WRITE_ONCE() in mptcp_active_disable(). */
        timeout = READ_ONCE(pernet->active_disable_stamp) +
                  multiplier * blackhole_timeout * HZ;

        return time_before(jiffies, timeout);
}

/* Enable active MPTCP and reset active_disable_times if needed */
void mptcp_active_enable(struct sock *sk)
{
        struct mptcp_pernet *pernet = mptcp_get_pernet(sock_net(sk));

        if (atomic_read(&pernet->active_disable_times)) {
                struct net_device *dev;
                struct dst_entry *dst;

                rcu_read_lock();
                dst = __sk_dst_get(sk);
                dev = dst ? dst_dev_rcu(dst) : NULL;
                if (!(dev && (dev->flags & IFF_LOOPBACK)))
                        atomic_set(&pernet->active_disable_times, 0);
                rcu_read_unlock();
        }
}

/* Check the number of retransmissions, and fallback to TCP if needed */
void mptcp_active_detect_blackhole(struct sock *ssk, bool expired)
{
        struct mptcp_subflow_context *subflow;
        u8 timeouts, to_max;
        struct net *net;

        /* Only check MPTCP SYN ... */
        if (likely(!sk_is_mptcp(ssk) || ssk->sk_state != TCP_SYN_SENT))
                return;

        subflow = mptcp_subflow_ctx(ssk);

        /* ... + MP_CAPABLE */
        if (!subflow->request_mptcp) {
                /* Mark as blackhole iif the 1st non-MPTCP SYN is accepted */
                subflow->mpc_drop = 0;
                return;
        }

        net = sock_net(ssk);
        timeouts = inet_csk(ssk)->icsk_retransmits;
        to_max = mptcp_get_pernet(net)->syn_retrans_before_tcp_fallback;

        if (timeouts == to_max || (timeouts < to_max && expired)) {
                subflow->mpc_drop = 1;
                mptcp_early_fallback(mptcp_sk(subflow->conn), subflow,
                                     MPTCP_MIB_MPCAPABLEACTIVEDROP);
        }
}

static int __net_init mptcp_net_init(struct net *net)
{
        struct mptcp_pernet *pernet = mptcp_get_pernet(net);

        mptcp_pernet_set_defaults(pernet);

        return mptcp_pernet_new_table(net, pernet);
}

/* Note: the callback will only be called per extra netns */
static void __net_exit mptcp_net_exit(struct net *net)
{
        struct mptcp_pernet *pernet = mptcp_get_pernet(net);

        mptcp_pernet_del_table(pernet);
}

static struct pernet_operations mptcp_pernet_ops = {
        .init = mptcp_net_init,
        .exit = mptcp_net_exit,
        .id = &mptcp_pernet_id,
        .size = sizeof(struct mptcp_pernet),
};

void __init mptcp_init(void)
{
        mptcp_join_cookie_init();
        mptcp_proto_init();

        if (register_pernet_subsys(&mptcp_pernet_ops) < 0)
                panic("Failed to register MPTCP pernet subsystem.\n");
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
int __init mptcpv6_init(void)
{
        int err;

        err = mptcp_proto_v6_init();

        return err;
}
#endif