// SPDX-License-Identifier: GPL-2.0
/*
 * To speed up listener socket lookup, create an array to store all sockets
 * listening on the same port.  This allows a decision to be made after finding
 * the first socket.  An optional BPF program can also be configured for
 * selecting the socket index from the array of available sockets.
 */

#include <net/ip.h>
#include <net/sock_reuseport.h>
#include <linux/bpf.h>
#include <linux/idr.h>
#include <linux/filter.h>
#include <linux/rcupdate.h>

#define INIT_SOCKS 128

DEFINE_SPINLOCK(reuseport_lock);

static DEFINE_IDA(reuseport_ida);
static int reuseport_resurrect(struct sock *sk, struct sock_reuseport *old_reuse,
                               struct sock_reuseport *reuse, bool bind_inany);

static int reuseport_sock_index(struct sock *sk,
                                const struct sock_reuseport *reuse,
                                bool closed)
{
        int left, right;

        if (!closed) {
                left = 0;
                right = reuse->num_socks;
        } else {
                left = reuse->max_socks - reuse->num_closed_socks;
                right = reuse->max_socks;
        }

        for (; left < right; left++)
                if (reuse->socks[left] == sk)
                        return left;
        return -1;
}

static void __reuseport_add_sock(struct sock *sk,
                                 struct sock_reuseport *reuse)
{
        reuse->socks[reuse->num_socks] = sk;
        /* paired with smp_rmb() in reuseport_(select|migrate)_sock() */
        smp_wmb();
        reuse->num_socks++;
}

static bool __reuseport_detach_sock(struct sock *sk,
                                    struct sock_reuseport *reuse)
{
        int i = reuseport_sock_index(sk, reuse, false);

        if (i == -1)
                return false;

        reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
        reuse->num_socks--;

        return true;
}

static void __reuseport_add_closed_sock(struct sock *sk,
                                        struct sock_reuseport *reuse)
{
        reuse->socks[reuse->max_socks - reuse->num_closed_socks - 1] = sk;
        /* paired with READ_ONCE() in inet_csk_bind_conflict() */
        WRITE_ONCE(reuse->num_closed_socks, reuse->num_closed_socks + 1);
}

static bool __reuseport_detach_closed_sock(struct sock *sk,
                                           struct sock_reuseport *reuse)
{
        int i = reuseport_sock_index(sk, reuse, true);

        if (i == -1)
                return false;

        reuse->socks[i] = reuse->socks[reuse->max_socks - reuse->num_closed_socks];
        /* paired with READ_ONCE() in inet_csk_bind_conflict() */
        WRITE_ONCE(reuse->num_closed_socks, reuse->num_closed_socks - 1);

        return true;
}

static struct sock_reuseport *__reuseport_alloc(unsigned int max_socks)
{
        unsigned int size = sizeof(struct sock_reuseport) +
                      sizeof(struct sock *) * max_socks;
        struct sock_reuseport *reuse = kzalloc(size, GFP_ATOMIC);

        if (!reuse)
                return NULL;

        reuse->max_socks = max_socks;

        RCU_INIT_POINTER(reuse->prog, NULL);
        return reuse;
}

int reuseport_alloc(struct sock *sk, bool bind_inany)
{
        struct sock_reuseport *reuse;
        int id, ret = 0;

        /* bh lock used since this function call may precede hlist lock in
         * soft irq of receive path or setsockopt from process context
         */
        spin_lock_bh(&reuseport_lock);

        /* Allocation attempts can occur concurrently via the setsockopt path
         * and the bind/hash path.  Nothing to do when we lose the race.
         */
        reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
                                          lockdep_is_held(&reuseport_lock));
        if (reuse) {
                if (reuse->num_closed_socks) {
                        /* sk was shutdown()ed before */
                        ret = reuseport_resurrect(sk, reuse, NULL, bind_inany);
                        goto out;
                }

                /* Only set reuse->bind_inany if the bind_inany is true.
                 * Otherwise, it will overwrite the reuse->bind_inany
                 * which was set by the bind/hash path.
                 */
                if (bind_inany)
                        reuse->bind_inany = bind_inany;
                goto out;
        }

        reuse = __reuseport_alloc(INIT_SOCKS);
        if (!reuse) {
                ret = -ENOMEM;
                goto out;
        }

        id = ida_alloc(&reuseport_ida, GFP_ATOMIC);
        if (id < 0) {
                kfree(reuse);
                ret = id;
                goto out;
        }

        reuse->reuseport_id = id;
        reuse->bind_inany = bind_inany;
        reuse->socks[0] = sk;
        reuse->num_socks = 1;
        rcu_assign_pointer(sk->sk_reuseport_cb, reuse);

out:
        spin_unlock_bh(&reuseport_lock);

        return ret;
}
EXPORT_SYMBOL(reuseport_alloc);

static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse)
{
        struct sock_reuseport *more_reuse;
        u32 more_socks_size, i;

        more_socks_size = reuse->max_socks * 2U;
        if (more_socks_size > U16_MAX) {
                if (reuse->num_closed_socks) {
                        /* Make room by removing a closed sk.
                         * The child has already been migrated.
                         * Only reqsk left at this point.
                         */
                        struct sock *sk;

                        sk = reuse->socks[reuse->max_socks - reuse->num_closed_socks];
                        RCU_INIT_POINTER(sk->sk_reuseport_cb, NULL);
                        __reuseport_detach_closed_sock(sk, reuse);

                        return reuse;
                }

                return NULL;
        }

        more_reuse = __reuseport_alloc(more_socks_size);
        if (!more_reuse)
                return NULL;

        more_reuse->num_socks = reuse->num_socks;
        more_reuse->num_closed_socks = reuse->num_closed_socks;
        more_reuse->prog = reuse->prog;
        more_reuse->reuseport_id = reuse->reuseport_id;
        more_reuse->bind_inany = reuse->bind_inany;
        more_reuse->has_conns = reuse->has_conns;

        memcpy(more_reuse->socks, reuse->socks,
               reuse->num_socks * sizeof(struct sock *));
        memcpy(more_reuse->socks +
               (more_reuse->max_socks - more_reuse->num_closed_socks),
               reuse->socks + (reuse->max_socks - reuse->num_closed_socks),
               reuse->num_closed_socks * sizeof(struct sock *));
        more_reuse->synq_overflow_ts = READ_ONCE(reuse->synq_overflow_ts);

        for (i = 0; i < reuse->max_socks; ++i)
                rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
                                   more_reuse);

        /* Note: we use kfree_rcu here instead of reuseport_free_rcu so
         * that reuse and more_reuse can temporarily share a reference
         * to prog.
         */
        kfree_rcu(reuse, rcu);
        return more_reuse;
}

static void reuseport_free_rcu(struct rcu_head *head)
{
        struct sock_reuseport *reuse;

        reuse = container_of(head, struct sock_reuseport, rcu);
        sk_reuseport_prog_free(rcu_dereference_protected(reuse->prog, 1));
        ida_free(&reuseport_ida, reuse->reuseport_id);
        kfree(reuse);
}

/**
 *  reuseport_add_sock - Add a socket to the reuseport group of another.
 *  @sk:  New socket to add to the group.
 *  @sk2: Socket belonging to the existing reuseport group.
 *  @bind_inany: Whether or not the group is bound to a local INANY address.
 *
 *  May return ENOMEM and not add socket to group under memory pressure.
 */
int reuseport_add_sock(struct sock *sk, struct sock *sk2, bool bind_inany)
{
        struct sock_reuseport *old_reuse, *reuse;

        if (!rcu_access_pointer(sk2->sk_reuseport_cb)) {
                int err = reuseport_alloc(sk2, bind_inany);

                if (err)
                        return err;
        }

        spin_lock_bh(&reuseport_lock);
        reuse = rcu_dereference_protected(sk2->sk_reuseport_cb,
                                          lockdep_is_held(&reuseport_lock));
        old_reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
                                              lockdep_is_held(&reuseport_lock));
        if (old_reuse && old_reuse->num_closed_socks) {
                /* sk was shutdown()ed before */
                int err = reuseport_resurrect(sk, old_reuse, reuse, reuse->bind_inany);

                spin_unlock_bh(&reuseport_lock);
                return err;
        }

        if (old_reuse && old_reuse->num_socks != 1) {
                spin_unlock_bh(&reuseport_lock);
                return -EBUSY;
        }

        if (reuse->num_socks + reuse->num_closed_socks == reuse->max_socks) {
                reuse = reuseport_grow(reuse);
                if (!reuse) {
                        spin_unlock_bh(&reuseport_lock);
                        return -ENOMEM;
                }
        }

        __reuseport_add_sock(sk, reuse);
        rcu_assign_pointer(sk->sk_reuseport_cb, reuse);

        spin_unlock_bh(&reuseport_lock);

        if (old_reuse)
                call_rcu(&old_reuse->rcu, reuseport_free_rcu);
        return 0;
}
EXPORT_SYMBOL(reuseport_add_sock);

static int reuseport_resurrect(struct sock *sk, struct sock_reuseport *old_reuse,
                               struct sock_reuseport *reuse, bool bind_inany)
{
        if (old_reuse == reuse) {
                /* If sk was in the same reuseport group, just pop sk out of
                 * the closed section and push sk into the listening section.
                 */
                __reuseport_detach_closed_sock(sk, old_reuse);
                __reuseport_add_sock(sk, old_reuse);
                return 0;
        }

        if (!reuse) {
                /* In bind()/listen() path, we cannot carry over the eBPF prog
                 * for the shutdown()ed socket. In setsockopt() path, we should
                 * not change the eBPF prog of listening sockets by attaching a
                 * prog to the shutdown()ed socket. Thus, we will allocate a new
                 * reuseport group and detach sk from the old group.
                 */
                int id;

                reuse = __reuseport_alloc(INIT_SOCKS);
                if (!reuse)
                        return -ENOMEM;

                id = ida_alloc(&reuseport_ida, GFP_ATOMIC);
                if (id < 0) {
                        kfree(reuse);
                        return id;
                }

                reuse->reuseport_id = id;
                reuse->bind_inany = bind_inany;
        } else {
                /* Move sk from the old group to the new one if
                 * - all the other listeners in the old group were close()d or
                 *   shutdown()ed, and then sk2 has listen()ed on the same port
                 * OR
                 * - sk listen()ed without bind() (or with autobind), was
                 *   shutdown()ed, and then listen()s on another port which
                 *   sk2 listen()s on.
                 */
                if (reuse->num_socks + reuse->num_closed_socks == reuse->max_socks) {
                        reuse = reuseport_grow(reuse);
                        if (!reuse)
                                return -ENOMEM;
                }
        }

        __reuseport_detach_closed_sock(sk, old_reuse);
        __reuseport_add_sock(sk, reuse);
        rcu_assign_pointer(sk->sk_reuseport_cb, reuse);

        if (old_reuse->num_socks + old_reuse->num_closed_socks == 0)
                call_rcu(&old_reuse->rcu, reuseport_free_rcu);

        return 0;
}

void reuseport_detach_sock(struct sock *sk)
{
        struct sock_reuseport *reuse;

        spin_lock_bh(&reuseport_lock);
        reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
                                          lockdep_is_held(&reuseport_lock));

        /* reuseport_grow() has detached a closed sk */
        if (!reuse)
                goto out;

        /* Notify the bpf side. The sk may be added to a sockarray
         * map. If so, sockarray logic will remove it from the map.
         *
         * Other bpf map types that work with reuseport, like sockmap,
         * don't need an explicit callback from here. They override sk
         * unhash/close ops to remove the sk from the map before we
         * get to this point.
         */
        bpf_sk_reuseport_detach(sk);

        rcu_assign_pointer(sk->sk_reuseport_cb, NULL);

        if (!__reuseport_detach_closed_sock(sk, reuse))
                __reuseport_detach_sock(sk, reuse);

        if (reuse->num_socks + reuse->num_closed_socks == 0)
                call_rcu(&reuse->rcu, reuseport_free_rcu);

out:
        spin_unlock_bh(&reuseport_lock);
}
EXPORT_SYMBOL(reuseport_detach_sock);

void reuseport_stop_listen_sock(struct sock *sk)
{
        if (sk->sk_protocol == IPPROTO_TCP) {
                struct sock_reuseport *reuse;
                struct bpf_prog *prog;

                spin_lock_bh(&reuseport_lock);

                reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
                                                  lockdep_is_held(&reuseport_lock));
                prog = rcu_dereference_protected(reuse->prog,
                                                 lockdep_is_held(&reuseport_lock));

                if (sock_net(sk)->ipv4.sysctl_tcp_migrate_req ||
                    (prog && prog->expected_attach_type == BPF_SK_REUSEPORT_SELECT_OR_MIGRATE)) {
                        /* Migration capable, move sk from the listening section
                         * to the closed section.
                         */
                        bpf_sk_reuseport_detach(sk);

                        __reuseport_detach_sock(sk, reuse);
                        __reuseport_add_closed_sock(sk, reuse);

                        spin_unlock_bh(&reuseport_lock);
                        return;
                }

                spin_unlock_bh(&reuseport_lock);
        }

        /* Not capable to do migration, detach immediately */
        reuseport_detach_sock(sk);
}
EXPORT_SYMBOL(reuseport_stop_listen_sock);

static struct sock *run_bpf_filter(struct sock_reuseport *reuse, u16 socks,
                                   struct bpf_prog *prog, struct sk_buff *skb,
                                   int hdr_len)
{
        struct sk_buff *nskb = NULL;
        u32 index;

        if (skb_shared(skb)) {
                nskb = skb_clone(skb, GFP_ATOMIC);
                if (!nskb)
                        return NULL;
                skb = nskb;
        }

        /* temporarily advance data past protocol header */
        if (!pskb_pull(skb, hdr_len)) {
                kfree_skb(nskb);
                return NULL;
        }
        index = bpf_prog_run_save_cb(prog, skb);
        __skb_push(skb, hdr_len);

        consume_skb(nskb);

        if (index >= socks)
                return NULL;

        return reuse->socks[index];
}

static struct sock *reuseport_select_sock_by_hash(struct sock_reuseport *reuse,
                                                  u32 hash, u16 num_socks)
{
        int i, j;

        i = j = reciprocal_scale(hash, num_socks);
        while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {
                i++;
                if (i >= num_socks)
                        i = 0;
                if (i == j)
                        return NULL;
        }

        return reuse->socks[i];
}

/**
 *  reuseport_select_sock - Select a socket from an SO_REUSEPORT group.
 *  @sk: First socket in the group.
 *  @hash: When no BPF filter is available, use this hash to select.
 *  @skb: skb to run through BPF filter.
 *  @hdr_len: BPF filter expects skb data pointer at payload data.  If
 *    the skb does not yet point at the payload, this parameter represents
 *    how far the pointer needs to advance to reach the payload.
 *  Returns a socket that should receive the packet (or NULL on error).
 */
struct sock *reuseport_select_sock(struct sock *sk,
                                   u32 hash,
                                   struct sk_buff *skb,
                                   int hdr_len)
{
        struct sock_reuseport *reuse;
        struct bpf_prog *prog;
        struct sock *sk2 = NULL;
        u16 socks;

        rcu_read_lock();
        reuse = rcu_dereference(sk->sk_reuseport_cb);

        /* if memory allocation failed or add call is not yet complete */
        if (!reuse)
                goto out;

        prog = rcu_dereference(reuse->prog);
        socks = READ_ONCE(reuse->num_socks);
        if (likely(socks)) {
                /* paired with smp_wmb() in __reuseport_add_sock() */
                smp_rmb();

                if (!prog || !skb)
                        goto select_by_hash;

                if (prog->type == BPF_PROG_TYPE_SK_REUSEPORT)
                        sk2 = bpf_run_sk_reuseport(reuse, sk, prog, skb, NULL, hash);
                else
                        sk2 = run_bpf_filter(reuse, socks, prog, skb, hdr_len);

select_by_hash:
                /* no bpf or invalid bpf result: fall back to hash usage */
                if (!sk2)
                        sk2 = reuseport_select_sock_by_hash(reuse, hash, socks);
        }

out:
        rcu_read_unlock();
        return sk2;
}
EXPORT_SYMBOL(reuseport_select_sock);

/**
 *  reuseport_migrate_sock - Select a socket from an SO_REUSEPORT group.
 *  @sk: close()ed or shutdown()ed socket in the group.
 *  @migrating_sk: ESTABLISHED/SYN_RECV full socket in the accept queue or
 *    NEW_SYN_RECV request socket during 3WHS.
 *  @skb: skb to run through BPF filter.
 *  Returns a socket (with sk_refcnt +1) that should accept the child socket
 *  (or NULL on error).
 */
struct sock *reuseport_migrate_sock(struct sock *sk,
                                    struct sock *migrating_sk,
                                    struct sk_buff *skb)
{
        struct sock_reuseport *reuse;
        struct sock *nsk = NULL;
        bool allocated = false;
        struct bpf_prog *prog;
        u16 socks;
        u32 hash;

        rcu_read_lock();

        reuse = rcu_dereference(sk->sk_reuseport_cb);
        if (!reuse)
                goto out;

        socks = READ_ONCE(reuse->num_socks);
        if (unlikely(!socks))
                goto failure;

        /* paired with smp_wmb() in __reuseport_add_sock() */
        smp_rmb();

        hash = migrating_sk->sk_hash;
        prog = rcu_dereference(reuse->prog);
        if (!prog || prog->expected_attach_type != BPF_SK_REUSEPORT_SELECT_OR_MIGRATE) {
                if (sock_net(sk)->ipv4.sysctl_tcp_migrate_req)
                        goto select_by_hash;
                goto failure;
        }

        if (!skb) {
                skb = alloc_skb(0, GFP_ATOMIC);
                if (!skb)
                        goto failure;
                allocated = true;
        }

        nsk = bpf_run_sk_reuseport(reuse, sk, prog, skb, migrating_sk, hash);

        if (allocated)
                kfree_skb(skb);

select_by_hash:
        if (!nsk)
                nsk = reuseport_select_sock_by_hash(reuse, hash, socks);

        if (IS_ERR_OR_NULL(nsk) || unlikely(!refcount_inc_not_zero(&nsk->sk_refcnt))) {
                nsk = NULL;
                goto failure;
        }

out:
        rcu_read_unlock();
        return nsk;

failure:
        __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
        goto out;
}
EXPORT_SYMBOL(reuseport_migrate_sock);

int reuseport_attach_prog(struct sock *sk, struct bpf_prog *prog)
{
        struct sock_reuseport *reuse;
        struct bpf_prog *old_prog;

        if (sk_unhashed(sk)) {
                int err;

                if (!sk->sk_reuseport)
                        return -EINVAL;

                err = reuseport_alloc(sk, false);
                if (err)
                        return err;
        } else if (!rcu_access_pointer(sk->sk_reuseport_cb)) {
                /* The socket wasn't bound with SO_REUSEPORT */
                return -EINVAL;
        }

        spin_lock_bh(&reuseport_lock);
        reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
                                          lockdep_is_held(&reuseport_lock));
        old_prog = rcu_dereference_protected(reuse->prog,
                                             lockdep_is_held(&reuseport_lock));
        rcu_assign_pointer(reuse->prog, prog);
        spin_unlock_bh(&reuseport_lock);

        sk_reuseport_prog_free(old_prog);
        return 0;
}
EXPORT_SYMBOL(reuseport_attach_prog);

int reuseport_detach_prog(struct sock *sk)
{
        struct sock_reuseport *reuse;
        struct bpf_prog *old_prog;

        old_prog = NULL;
        spin_lock_bh(&reuseport_lock);
        reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
                                          lockdep_is_held(&reuseport_lock));

        /* reuse must be checked after acquiring the reuseport_lock
         * because reuseport_grow() can detach a closed sk.
         */
        if (!reuse) {
                spin_unlock_bh(&reuseport_lock);
                return sk->sk_reuseport ? -ENOENT : -EINVAL;
        }

        if (sk_unhashed(sk) && reuse->num_closed_socks) {
                spin_unlock_bh(&reuseport_lock);
                return -ENOENT;
        }

        old_prog = rcu_replace_pointer(reuse->prog, old_prog,
                                       lockdep_is_held(&reuseport_lock));
        spin_unlock_bh(&reuseport_lock);

        if (!old_prog)
                return -ENOENT;

        sk_reuseport_prog_free(old_prog);
        return 0;
}
EXPORT_SYMBOL(reuseport_detach_prog);