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

From: Daniel Borkmann <[email-masked]>
Date: Thu, 02 Feb 2017 22:23:04 +0100

On 02/02/2017 09:59 PM, Chenbo Feng wrote:
> From: Chenbo Feng <[email-masked]>
>
> 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 <[email-masked]>
> ---
>   include/linux/bpf.h       |  1 +
>   include/linux/sock_diag.h |  1 +
>   include/uapi/linux/bpf.h  |  9 ++++++++-
>   net/core/filter.c         | 15 +++++++++++++++
>   net/core/sock_diag.c      |  3 ++-
>   5 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 3ed1f3b1d594..3f2e0af28c6e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -349,6 +349,7 @@ extern const struct bpf_func_proto bpf_get_current_comm_proto;
>   extern const struct bpf_func_proto bpf_skb_vlan_push_proto;
>   extern const struct bpf_func_proto bpf_skb_vlan_pop_proto;
>   extern const struct bpf_func_proto bpf_get_stackid_proto;
> +extern const struct bpf_func_proto bpf_get_socket_cookie_proto;

I don't think this needs to be added here.

>   /* Shared helpers among cBPF and eBPF. */
>   void bpf_user_rnd_init_once(void);
> diff --git a/include/linux/sock_diag.h b/include/linux/sock_diag.h
> index a0596ca0e80a..a2f8109bb215 100644
> --- a/include/linux/sock_diag.h
> +++ b/include/linux/sock_diag.h
> @@ -24,6 +24,7 @@ void sock_diag_unregister(const struct sock_diag_handler *h);
>   void sock_diag_register_inet_compat(int (*fn)(struct sk_buff *skb, struct nlmsghdr *nlh));
>   void sock_diag_unregister_inet_compat(int (*fn)(struct sk_buff *skb, struct nlmsghdr *nlh));
>
> +u64 sock_gen_cookie(struct sock *sk);
>   int sock_diag_check_cookie(struct sock *sk, const __u32 *cookie);
>   void sock_diag_save_cookie(struct sock *sk, __u32 *cookie);
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 0eb0e87dbe9f..62ee5fab08e5 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -430,6 +430,12 @@ union bpf_attr {
>    *     @xdp_md: pointer to xdp_md
>    *     @delta: An positive/negative integer to be added to xdp_md.data
>    *     Return: 0 on success or negative on error
> + *
> + * u64 bpf_bpf_get_socket_cookie(skb)
> + *     Get the cookie for the socket stored inside sk_buff.
> + *     @skb: pointer to skb
> + *     Return: 8 Bytes non-decreasing number on success or 0 if the socket
> + *     field is missing inside sk_buff
>    */
>   #define __BPF_FUNC_MAPPER(FN)		\
>   	FN(unspec),			\
> @@ -476,7 +482,8 @@ union bpf_attr {
>   	FN(set_hash_invalid),		\
>   	FN(get_numa_node_id),		\
>   	FN(skb_change_head),		\
> -	FN(xdp_adjust_head),
> +	FN(xdp_adjust_head),		\
> +	FN(get_socket_cookie),

Looks like you need a rebase to net-next, since probe_read_str() helper
was added in the meantime.

>   /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>    * function eBPF program intends to call
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 1969b3f118c1..913b14d3b484 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>
> @@ -2597,6 +2598,18 @@ static const struct bpf_func_proto bpf_xdp_event_output_proto = {
>   	.arg5_type	= ARG_CONST_STACK_SIZE,
>   };
>
> +BPF_CALL_1(bpf_get_socket_cookie, struct sk_buff *, skb)
> +{
> +	return skb->sk ? sock_gen_cookie(skb->sk) : 0;
> +}
> +
> +const struct bpf_func_proto bpf_get_socket_cookie_proto = {

static const struct bpf_func_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 *
>   sk_filter_func_proto(enum bpf_func_id func_id)
>   {
> @@ -2620,6 +2633,8 @@ sk_filter_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;
>   	}
> diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c
> index 6b10573cc9fa..b07b0a784f33 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);
> @@ -30,6 +30,7 @@ static u64 sock_gen_cookie(struct sock *sk)
>   		atomic64_cmpxchg(&sk->sk_cookie, 0, res);
>   	}
>   }
> +EXPORT_SYMBOL_GPL(sock_gen_cookie);

Also no need to export via EXPORT_SYMBOL_GPL().

>   int sock_diag_check_cookie(struct sock *sk, const __u32 *cookie)
>   {
>