netdev - Re: [PATCH bpf-next v2 04/11] tcp_bpf: Don't let child socket inherit parent protocol ops on copy

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Date:   Mon, 13 Jan 2020 22:23:45 +0000
From:   Martin Lau <kafai@...com>
To:     Jakub Sitnicki <jakub@...udflare.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-team@...udflare.com" <kernel-team@...udflare.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "John Fastabend" <john.fastabend@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [PATCH bpf-next v2 04/11] tcp_bpf: Don't let child socket inherit
 parent protocol ops on copy

On Fri, Jan 10, 2020 at 11:50:20AM +0100, Jakub Sitnicki wrote:
> Prepare for cloning listening sockets that have their protocol callbacks
> overridden by sk_msg. Child sockets must not inherit parent callbacks that
> access state stored in sk_user_data owned by the parent.
> 
> Restore the child socket protocol callbacks before the it gets hashed and
> any of the callbacks can get invoked.
> 
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> ---
>  include/net/tcp.h        |  1 +
>  net/ipv4/tcp_bpf.c       | 13 +++++++++++++
>  net/ipv4/tcp_minisocks.c |  2 ++
>  3 files changed, 16 insertions(+)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 9dd975be7fdf..7cbf9465bb10 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2181,6 +2181,7 @@ int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
>  		    int nonblock, int flags, int *addr_len);
>  int __tcp_bpf_recvmsg(struct sock *sk, struct sk_psock *psock,
>  		      struct msghdr *msg, int len, int flags);
> +void tcp_bpf_clone(const struct sock *sk, struct sock *child);
>  
>  /* Call BPF_SOCK_OPS program that returns an int. If the return value
>   * is < 0, then the BPF op failed (for example if the loaded BPF
> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> index f6c83747c71e..6f96320fb7cf 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -586,6 +586,19 @@ static void tcp_bpf_close(struct sock *sk, long timeout)
>  	saved_close(sk, timeout);
>  }
>  
> +/* If a child got cloned from a listening socket that had tcp_bpf
> + * protocol callbacks installed, we need to restore the callbacks to
> + * the default ones because the child does not inherit the psock state
> + * that tcp_bpf callbacks expect.
> + */
> +void tcp_bpf_clone(const struct sock *sk, struct sock *newsk)
> +{
> +	struct proto *prot = newsk->sk_prot;
> +
> +	if (prot->recvmsg == tcp_bpf_recvmsg)
A question not related to this patch (may be it is more for patch 6).

How tcp_bpf_recvmsg may be used for a listening sock (sk here)?

> +		newsk->sk_prot = sk->sk_prot_creator;
> +}
> +