Re: [PATCH v1 bpf-next 09/11] bpf: Support bpf_get_socket_cookie_sock() for BPF_PROG_TYPE_SK_REUSEPORT.

[Martin KaFai Lau]

On Tue, Dec 01, 2020 at 11:44:16PM +0900, Kuniyuki Iwashima wrote:
> We will call sock_reuseport.prog for socket migration in the next commit,
> so the eBPF program has to know which listener is closing in order to
> select the new listener.
> 
> Currently, we can get a unique ID for each listener in the userspace by
> calling bpf_map_lookup_elem() for BPF_MAP_TYPE_REUSEPORT_SOCKARRAY map.
> 
> This patch makes the sk pointer available in sk_reuseport_md so that we can
> get the ID by BPF_FUNC_get_socket_cookie() in the eBPF program.
> 
> Link: https://lore.kernel.org/netdev/20201119001154.kapwihc2plp4f7zc@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> Suggested-by: Martin KaFai Lau <kafai@xxxxxx>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx>
> ---
>  include/uapi/linux/bpf.h       |  8 ++++++++
>  net/core/filter.c              | 12 +++++++++++-
>  tools/include/uapi/linux/bpf.h |  8 ++++++++
>  3 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index efe342bf3dbc..3e9b8bd42b4e 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1650,6 +1650,13 @@ union bpf_attr {
>   * 		A 8-byte long non-decreasing number on success, or 0 if the
>   * 		socket field is missing inside *skb*.
>   *
> + * u64 bpf_get_socket_cookie(struct bpf_sock *sk)
> + * 	Description
> + * 		Equivalent to bpf_get_socket_cookie() helper that accepts
> + * 		*skb*, but gets socket from **struct bpf_sock** context.
> + * 	Return
> + * 		A 8-byte long non-decreasing number.
> + *
>   * u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)
>   * 	Description
>   * 		Equivalent to bpf_get_socket_cookie() helper that accepts
> @@ -4420,6 +4427,7 @@ struct sk_reuseport_md {
>  	__u32 bind_inany;	/* Is sock bound to an INANY address? */
>  	__u32 hash;		/* A hash of the packet 4 tuples */
>  	__u8 migration;		/* Migration type */
> +	__bpf_md_ptr(struct bpf_sock *, sk); /* current listening socket */
>  };
>  
>  #define BPF_TAG_SIZE	8
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 0a0634787bb4..1059d31847ef 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4628,7 +4628,7 @@ static const struct bpf_func_proto bpf_get_socket_cookie_sock_proto = {
>  	.func		= bpf_get_socket_cookie_sock,
>  	.gpl_only	= false,
>  	.ret_type	= RET_INTEGER,
> -	.arg1_type	= ARG_PTR_TO_CTX,
> +	.arg1_type	= ARG_PTR_TO_SOCKET,
This will break existing bpf prog (BPF_PROG_TYPE_CGROUP_SOCK)
using this proto.  A new proto is needed and there is
an on-going patch doing this [0].

[0]: https://lore.kernel.org/bpf/20201203213330.1657666-1-revest@xxxxxxxxxx/