// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2021 Cong Wang <cong.wang@bytedance.com> */

#include <linux/bpf.h>
#include <linux/skmsg.h>
#include <net/af_unix.h>

#include "af_unix.h"

#define unix_sk_has_data(__sk, __psock)                                 \
                ({      !skb_queue_empty(&__sk->sk_receive_queue) ||    \
                        !skb_queue_empty(&__psock->ingress_skb) ||      \
                        !list_empty(&__psock->ingress_msg);             \
                })

static int unix_msg_wait_data(struct sock *sk, struct sk_psock *psock,
                              long timeo)
{
        DEFINE_WAIT_FUNC(wait, woken_wake_function);
        struct unix_sock *u = unix_sk(sk);
        int ret = 0;

        if (sk->sk_shutdown & RCV_SHUTDOWN)
                return 1;

        if (!timeo)
                return ret;

        add_wait_queue(sk_sleep(sk), &wait);
        sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        if (!unix_sk_has_data(sk, psock)) {
                mutex_unlock(&u->iolock);
                wait_woken(&wait, TASK_INTERRUPTIBLE, timeo);
                mutex_lock(&u->iolock);
                ret = unix_sk_has_data(sk, psock);
        }
        sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        remove_wait_queue(sk_sleep(sk), &wait);
        return ret;
}

static int __unix_recvmsg(struct sock *sk, struct msghdr *msg,
                          size_t len, int flags)
{
        if (sk->sk_type == SOCK_DGRAM)
                return __unix_dgram_recvmsg(sk, msg, len, flags);
        else
                return __unix_stream_recvmsg(sk, msg, len, flags);
}

static int unix_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
                            size_t len, int flags, int *addr_len)
{
        struct unix_sock *u = unix_sk(sk);
        struct sk_psock *psock;
        int copied;

        if (flags & MSG_OOB)
                return -EOPNOTSUPP;

        if (!len)
                return 0;

        psock = sk_psock_get(sk);
        if (unlikely(!psock))
                return __unix_recvmsg(sk, msg, len, flags);

        mutex_lock(&u->iolock);
        if (!skb_queue_empty(&sk->sk_receive_queue) &&
            sk_psock_queue_empty(psock)) {
                mutex_unlock(&u->iolock);
                sk_psock_put(sk, psock);
                return __unix_recvmsg(sk, msg, len, flags);
        }

msg_bytes_ready:
        copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
        if (!copied) {
                long timeo;
                int data;

                timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
                data = unix_msg_wait_data(sk, psock, timeo);
                if (data) {
                        if (!sk_psock_queue_empty(psock))
                                goto msg_bytes_ready;
                        mutex_unlock(&u->iolock);
                        sk_psock_put(sk, psock);
                        return __unix_recvmsg(sk, msg, len, flags);
                }
                copied = -EAGAIN;
        }
        mutex_unlock(&u->iolock);
        sk_psock_put(sk, psock);
        return copied;
}

static struct proto *unix_dgram_prot_saved __read_mostly;
static DEFINE_SPINLOCK(unix_dgram_prot_lock);
static struct proto unix_dgram_bpf_prot;

static struct proto *unix_stream_prot_saved __read_mostly;
static DEFINE_SPINLOCK(unix_stream_prot_lock);
static struct proto unix_stream_bpf_prot;

static void unix_dgram_bpf_rebuild_protos(struct proto *prot, const struct proto *base)
{
        *prot        = *base;
        prot->close  = sock_map_close;
        prot->recvmsg = unix_bpf_recvmsg;
        prot->sock_is_readable = sk_msg_is_readable;
}

static void unix_stream_bpf_rebuild_protos(struct proto *prot,
                                           const struct proto *base)
{
        *prot        = *base;
        prot->close  = sock_map_close;
        prot->recvmsg = unix_bpf_recvmsg;
        prot->sock_is_readable = sk_msg_is_readable;
        prot->unhash  = sock_map_unhash;
}

static void unix_dgram_bpf_check_needs_rebuild(struct proto *ops)
{
        if (unlikely(ops != smp_load_acquire(&unix_dgram_prot_saved))) {
                spin_lock_bh(&unix_dgram_prot_lock);
                if (likely(ops != unix_dgram_prot_saved)) {
                        unix_dgram_bpf_rebuild_protos(&unix_dgram_bpf_prot, ops);
                        smp_store_release(&unix_dgram_prot_saved, ops);
                }
                spin_unlock_bh(&unix_dgram_prot_lock);
        }
}

static void unix_stream_bpf_check_needs_rebuild(struct proto *ops)
{
        if (unlikely(ops != smp_load_acquire(&unix_stream_prot_saved))) {
                spin_lock_bh(&unix_stream_prot_lock);
                if (likely(ops != unix_stream_prot_saved)) {
                        unix_stream_bpf_rebuild_protos(&unix_stream_bpf_prot, ops);
                        smp_store_release(&unix_stream_prot_saved, ops);
                }
                spin_unlock_bh(&unix_stream_prot_lock);
        }
}

int unix_dgram_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)
{
        if (sk->sk_type != SOCK_DGRAM)
                return -EOPNOTSUPP;

        if (restore) {
                sk->sk_write_space = psock->saved_write_space;
                sock_replace_proto(sk, psock->sk_proto);
                return 0;
        }

        unix_dgram_bpf_check_needs_rebuild(psock->sk_proto);
        sock_replace_proto(sk, &unix_dgram_bpf_prot);
        return 0;
}

int unix_stream_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)
{
        struct sock *sk_pair;

        /* Restore does not decrement the sk_pair reference yet because we must
         * keep the a reference to the socket until after an RCU grace period
         * and any pending sends have completed.
         */
        if (restore) {
                sk->sk_write_space = psock->saved_write_space;
                sock_replace_proto(sk, psock->sk_proto);
                return 0;
        }

        /* psock_update_sk_prot can be called multiple times if psock is
         * added to multiple maps and/or slots in the same map. There is
         * also an edge case where replacing a psock with itself can trigger
         * an extra psock_update_sk_prot during the insert process. So it
         * must be safe to do multiple calls. Here we need to ensure we don't
         * increment the refcnt through sock_hold many times. There will only
         * be a single matching destroy operation.
         */
        if (!psock->sk_pair) {
                sk_pair = unix_peer(sk);
                sock_hold(sk_pair);
                psock->sk_pair = sk_pair;
        }

        unix_stream_bpf_check_needs_rebuild(psock->sk_proto);
        sock_replace_proto(sk, &unix_stream_bpf_prot);
        return 0;
}

void __init unix_bpf_build_proto(void)
{
        unix_dgram_bpf_rebuild_protos(&unix_dgram_bpf_prot, &unix_dgram_proto);
        unix_stream_bpf_rebuild_protos(&unix_stream_bpf_prot, &unix_stream_proto);

}