Re: [PATCH bpf-next 4/8] bpf, sockmap: Don't let child socket inherit psock or its ops on copy

[Martin Lau <kafai@fb.com>]

On Sat, Nov 23, 2019 at 12:07:47PM +0100, Jakub Sitnicki wrote:
[ ... ]

> @@ -370,6 +378,11 @@ static inline void sk_psock_restore_proto(struct sock *sk,
>  			sk->sk_prot = psock->sk_proto;
>  		psock->sk_proto = NULL;
>  	}
> +
> +	if (psock->icsk_af_ops) {
> +		icsk->icsk_af_ops = psock->icsk_af_ops;
> +		psock->icsk_af_ops = NULL;
> +	}
>  }

[ ... ]

> +static struct sock *tcp_bpf_syn_recv_sock(const struct sock *sk,
> +					  struct sk_buff *skb,
> +					  struct request_sock *req,
> +					  struct dst_entry *dst,
> +					  struct request_sock *req_unhash,
> +					  bool *own_req)
> +{
> +	const struct inet_connection_sock_af_ops *ops;
> +	void (*write_space)(struct sock *sk);
> +	struct sk_psock *psock;
> +	struct proto *proto;
> +	struct sock *child;
> +
> +	rcu_read_lock();
> +	psock = sk_psock(sk);
> +	if (likely(psock)) {
> +		proto = psock->sk_proto;
> +		write_space = psock->saved_write_space;
> +		ops = psock->icsk_af_ops;
It is not immediately clear to me what ensure
ops is not NULL here.

It is likely I missed something.  A short comment would
be very useful here.

> +	} else {
> +		ops = inet_csk(sk)->icsk_af_ops;
> +	}
> +	rcu_read_unlock();
> +
> +	child = ops->syn_recv_sock(sk, skb, req, dst, req_unhash, own_req);
> +
> +	/* Child must not inherit psock or its ops. */
> +	if (child && psock) {
> +		rcu_assign_sk_user_data(child, NULL);
> +		child->sk_prot = proto;
> +		child->sk_write_space = write_space;
> +
> +		/* v4-mapped sockets don't inherit parent ops. Don't restore. */
> +		if (inet_csk(child)->icsk_af_ops == inet_csk(sk)->icsk_af_ops)
> +			inet_csk(child)->icsk_af_ops = ops;
> +	}
> +	return child;
> +}
> +
>  enum {
>  	TCP_BPF_IPV4,
>  	TCP_BPF_IPV6,
> @@ -597,6 +642,7 @@ enum {
>  static struct proto *tcpv6_prot_saved __read_mostly;
>  static DEFINE_SPINLOCK(tcpv6_prot_lock);
>  static struct proto tcp_bpf_prots[TCP_BPF_NUM_PROTS][TCP_BPF_NUM_CFGS];
> +static struct inet_connection_sock_af_ops tcp_bpf_af_ops[TCP_BPF_NUM_PROTS];
>  
>  static void tcp_bpf_rebuild_protos(struct proto prot[TCP_BPF_NUM_CFGS],
>  				   struct proto *base)
> @@ -612,13 +658,23 @@ static void tcp_bpf_rebuild_protos(struct proto prot[TCP_BPF_NUM_CFGS],
>  	prot[TCP_BPF_TX].sendpage		= tcp_bpf_sendpage;
>  }
>  
> -static void tcp_bpf_check_v6_needs_rebuild(struct sock *sk, struct proto *ops)
> +static void tcp_bpf_rebuild_af_ops(struct inet_connection_sock_af_ops *ops,
> +				   const struct inet_connection_sock_af_ops *base)
> +{
> +	*ops = *base;
> +	ops->syn_recv_sock = tcp_bpf_syn_recv_sock;
> +}
> +
> +static void tcp_bpf_check_v6_needs_rebuild(struct sock *sk, struct proto *ops,
> +					   const struct inet_connection_sock_af_ops *af_ops)
>  {
>  	if (sk->sk_family == AF_INET6 &&
>  	    unlikely(ops != smp_load_acquire(&tcpv6_prot_saved))) {
>  		spin_lock_bh(&tcpv6_prot_lock);
>  		if (likely(ops != tcpv6_prot_saved)) {
>  			tcp_bpf_rebuild_protos(tcp_bpf_prots[TCP_BPF_IPV6], ops);
> +			tcp_bpf_rebuild_af_ops(&tcp_bpf_af_ops[TCP_BPF_IPV6],
> +					       af_ops);
>  			smp_store_release(&tcpv6_prot_saved, ops);
>  		}
>  		spin_unlock_bh(&tcpv6_prot_lock);
> @@ -628,6 +684,8 @@ static void tcp_bpf_check_v6_needs_rebuild(struct sock *sk, struct proto *ops)
>  static int __init tcp_bpf_v4_build_proto(void)
>  {
>  	tcp_bpf_rebuild_protos(tcp_bpf_prots[TCP_BPF_IPV4], &tcp_prot);
> +	tcp_bpf_rebuild_af_ops(&tcp_bpf_af_ops[TCP_BPF_IPV4], &ipv4_specific);
> +
>  	return 0;
>  }
>  core_initcall(tcp_bpf_v4_build_proto);
> @@ -637,7 +695,8 @@ static void tcp_bpf_update_sk_prot(struct sock *sk, struct sk_psock *psock)
>  	int family = sk->sk_family == AF_INET6 ? TCP_BPF_IPV6 : TCP_BPF_IPV4;
>  	int config = psock->progs.msg_parser   ? TCP_BPF_TX   : TCP_BPF_BASE;
>  
> -	sk_psock_update_proto(sk, psock, &tcp_bpf_prots[family][config]);
> +	sk_psock_update_proto(sk, psock, &tcp_bpf_prots[family][config],
> +			      &tcp_bpf_af_ops[family]);
>  }
>  
>  static void tcp_bpf_reinit_sk_prot(struct sock *sk, struct sk_psock *psock)
> @@ -677,6 +736,7 @@ void tcp_bpf_reinit(struct sock *sk)
>  
>  int tcp_bpf_init(struct sock *sk)
>  {
> +	struct inet_connection_sock *icsk = inet_csk(sk);
>  	struct proto *ops = READ_ONCE(sk->sk_prot);
>  	struct sk_psock *psock;
>  
> @@ -689,7 +749,7 @@ int tcp_bpf_init(struct sock *sk)
>  		rcu_read_unlock();
>  		return -EINVAL;
>  	}
> -	tcp_bpf_check_v6_needs_rebuild(sk, ops);
> +	tcp_bpf_check_v6_needs_rebuild(sk, ops, icsk->icsk_af_ops);
>  	tcp_bpf_update_sk_prot(sk, psock);
>  	rcu_read_unlock();
>  	return 0;
> -- 
> 2.20.1
>