On Wed, Mar 31, 2021 at 04:32 AM CEST, Cong Wang wrote:
> From: Cong Wang <cong.w...@bytedance.com>
>
> Currently sockmap calls into each protocol to update the struct
> proto and replace it. This certainly won't work when the protocol
> is implemented as a module, for example, AF_UNIX.
>
> Introduce a new ops sk->sk_prot->psock_update_sk_prot(), so each
> protocol can implement its own way to replace the struct proto.
> This also helps get rid of symbol dependencies on CONFIG_INET.
>
> Cc: John Fastabend <john.fastab...@gmail.com>
> Cc: Daniel Borkmann <dan...@iogearbox.net>
> Cc: Jakub Sitnicki <ja...@cloudflare.com>
> Cc: Lorenz Bauer <l...@cloudflare.com>
> Signed-off-by: Cong Wang <cong.w...@bytedance.com>
> ---

[...]

> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 4a0478b17243..38952aaee3a1 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2849,6 +2849,9 @@ struct proto udp_prot = {
>       .unhash                 = udp_lib_unhash,
>       .rehash                 = udp_v4_rehash,
>       .get_port               = udp_v4_get_port,
> +#ifdef CONFIG_BPF_SYSCALL
> +     .psock_update_sk_prot   = udp_bpf_update_proto,
> +#endif
>       .memory_allocated       = &udp_memory_allocated,
>       .sysctl_mem             = sysctl_udp_mem,
>       .sysctl_wmem_offset     = offsetof(struct net, 
> ipv4.sysctl_udp_wmem_min),
> diff --git a/net/ipv4/udp_bpf.c b/net/ipv4/udp_bpf.c
> index 7a94791efc1a..6001f93cd3a0 100644
> --- a/net/ipv4/udp_bpf.c
> +++ b/net/ipv4/udp_bpf.c
> @@ -41,12 +41,23 @@ static int __init udp_bpf_v4_build_proto(void)
>  }
>  core_initcall(udp_bpf_v4_build_proto);
>
> -struct proto *udp_bpf_get_proto(struct sock *sk, struct sk_psock *psock)
> +int udp_bpf_update_proto(struct sock *sk, bool restore)
>  {
>       int family = sk->sk_family == AF_INET ? UDP_BPF_IPV4 : UDP_BPF_IPV6;
> +     struct sk_psock *psock = sk_psock(sk);
> +
> +     if (restore) {
> +             sk->sk_write_space = psock->saved_write_space;
> +             /* Pairs with lockless read in sk_clone_lock() */

Just to clarify. UDP sockets don't get cloned, so the above comment
apply.

> +             WRITE_ONCE(sk->sk_prot, psock->sk_proto);
> +             return 0;
> +     }
>
>       if (sk->sk_family == AF_INET6)
>               udp_bpf_check_v6_needs_rebuild(psock->sk_proto);
>
> -     return &udp_bpf_prots[family];
> +     /* Pairs with lockless read in sk_clone_lock() */
> +     WRITE_ONCE(sk->sk_prot, &udp_bpf_prots[family]);
> +     return 0;
>  }
> +EXPORT_SYMBOL_GPL(udp_bpf_update_proto);

[...]

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