netdev - Re: [PATCH bpf-next v3 04/12] tcp_bpf: Don't let child socket inherit parent protocol ops on copy

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Date:   Wed, 22 Jan 2020 20:35:42 +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>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "John Fastabend" <john.fastabend@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [PATCH bpf-next v3 04/12] tcp_bpf: Don't let child socket inherit
 parent protocol ops on copy

On Wed, Jan 22, 2020 at 02:05:41PM +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 it gets hashed and any
> of the callbacks can get invoked.
> 
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> ---
>  include/net/tcp.h        |  7 +++++++
>  net/ipv4/tcp_bpf.c       | 13 +++++++++++++
>  net/ipv4/tcp_minisocks.c |  2 ++
>  3 files changed, 22 insertions(+)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 9dd975be7fdf..ac205d31e4ad 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2181,6 +2181,13 @@ 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);
> +#ifdef CONFIG_NET_SOCK_MSG
> +void tcp_bpf_clone(const struct sock *sk, struct sock *child);
nit.  "struct sock *child" vs ...

> +#else
> +static inline void tcp_bpf_clone(const struct sock *sk, struct sock *child)
> +{
> +}
> +#endif
>  
>  /* 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 4f25aba44ead..16060e0893a1 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -582,6 +582,19 @@ 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 sock *newsk" here.

Could be a follow-up.

Other than that,
Acked-by: Martin KaFai Lau <kafai@...com>

> +{
> +	struct proto *prot = newsk->sk_prot;
> +
> +	if (prot->unhash == tcp_bpf_unhash)
> +		newsk->sk_prot = sk->sk_prot_creator;
> +}
> +