unix_bpf.c

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

#include <linux/skmsg.h>
#include <linux/bpf.h>
#include <net/sock.h>
#include <net/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);

}