Re: [PATCH net-next v2 1/2] Add a helper function to get socket cookie in eBPF

[Daniel Borkmann <daniel@iogearbox.net>]

On 02/06/2017 03:17 AM, Chenbo Feng wrote:
> From: Chenbo Feng <fengc@google.com>
>
> Retrieve the socket cookie generated by sock_gen_cookie() from a sk_buff
> with a known socket. Generates a new cookie if one was not yet set.If
> the socket pointer inside sk_buff is NULL, 0 is returned. The helper
> function coud be useful in monitoring per socket networking traffic
> statistics and provide a unique socket identifier per namespace.
>
> Signed-off-by: Chenbo Feng <chenbofeng.kernel@gmail.com>
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 0b753cb..632fb91 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -26,6 +26,7 @@
>   #include <linux/mm.h>
>   #include <linux/fcntl.h>
>   #include <linux/socket.h>
> +#include <linux/sock_diag.h>
>   #include <linux/in.h>
>   #include <linux/inet.h>
>   #include <linux/netdevice.h>
> @@ -2599,6 +2600,18 @@ static const struct bpf_func_proto bpf_xdp_event_output_proto = {
>   	.arg5_type	= ARG_CONST_SIZE,
>   };
>
> +BPF_CALL_1(bpf_get_socket_cookie, struct sk_buff *, skb)
> +{
> +	return skb->sk ? sock_gen_cookie(skb->sk) : 0;
> +}
> +
> +static const struct bpf_func_proto bpf_get_socket_cookie_proto = {
> +	.func           = bpf_get_socket_cookie,
> +	.gpl_only       = false,
> +	.ret_type       = RET_INTEGER,
> +	.arg1_type      = ARG_PTR_TO_CTX,
> +};
> +
>   static const struct bpf_func_proto *
>   bpf_base_func_proto(enum bpf_func_id func_id)
>   {
> @@ -2622,6 +2635,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
>   	case BPF_FUNC_trace_printk:
>   		if (capable(CAP_SYS_ADMIN))
>   			return bpf_get_trace_printk_proto();
> +	case BPF_FUNC_get_socket_cookie:
> +		return &bpf_get_socket_cookie_proto;
>   	default:
>   		return NULL;
>   	}

This still has one issue that would need to be addressed, otherwise
looks good and ready to me.

Issue is that it cannot be added to bpf_base_func_proto(), because
that is also used by cg_sock_ops, which has struct sock as input
instead of struct sk_buff.

I suggest, we initially add this to both, sk_filter_func_proto() and
tc_cls_act_func_proto() and, if needed, we could follow-up with other
prog types at some later point in time. Otherwise, looks fine.

> diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c
> index 6b10573..acd2a6c 100644
> --- a/net/core/sock_diag.c
> +++ b/net/core/sock_diag.c
> @@ -19,7 +19,7 @@ static int (*inet_rcv_compat)(struct sk_buff *skb, struct nlmsghdr *nlh);
>   static DEFINE_MUTEX(sock_diag_table_mutex);
>   static struct workqueue_struct *broadcast_wq;
>
> -static u64 sock_gen_cookie(struct sock *sk)
> +u64 sock_gen_cookie(struct sock *sk)
>   {
>   	while (1) {
>   		u64 res = atomic64_read(&sk->sk_cookie);
>