[net-next,v8,2/3] Add a eBPF helper function to retrieve socket uid

From: Chenbo Feng <fengc@google.com>

Returns the owner uid of the socket inside a sk_buff. This is useful to
perform per-UID accounting of network traffic or per-UID packet
filtering. The socket need to be a fullsock otherwise overflowuid is
returned.

Signed-off-by: Chenbo Feng <fengc@google.com>
---
 include/uapi/linux/bpf.h       |  9 ++++++++-
 net/core/filter.c              | 22 ++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  3 ++-
 3 files changed, 32 insertions(+), 2 deletions(-)

On 23/03/2017 01:27, Chenbo Feng wrote:
> From: Chenbo Feng <fengc@google.com>
> 
> Returns the owner uid of the socket inside a sk_buff. This is useful to
> perform per-UID accounting of network traffic or per-UID packet
> filtering. The socket need to be a fullsock otherwise overflowuid is
> returned.
> 
> Signed-off-by: Chenbo Feng <fengc@google.com>
> ---
>  include/uapi/linux/bpf.h       |  9 ++++++++-
>  net/core/filter.c              | 22 ++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h |  3 ++-
>  3 files changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index dc81a9f..ff42111 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -462,6 +462,12 @@ union bpf_attr {
>   *     @skb: pointer to skb
>   *     Return: 8 Bytes non-decreasing number on success or 0 if the socket
>   *     field is missing inside sk_buff
> + *
> + * u32 bpf_get_socket_uid(skb)
> + *     Get the owner uid of the socket stored inside sk_buff.
> + *     @skb: pointer to skb
> + *     Return: uid of the socket owner on success or 0 if the socket pointer
> + *     inside sk_buff is NULL

What about UID 0? Why not returning -1 on error?

>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -510,7 +516,8 @@ union bpf_attr {
>  	FN(skb_change_head),		\
>  	FN(xdp_adjust_head),		\
>  	FN(probe_read_str),		\
> -	FN(get_socket_cookie),
> +	FN(get_socket_cookie),		\
> +	FN(get_socket_uid),
>  
>  /* 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 5b65ae3..93cc4af 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2612,6 +2612,24 @@ static const struct bpf_func_proto bpf_get_socket_cookie_proto = {
>  	.arg1_type      = ARG_PTR_TO_CTX,
>  };
>  
> +BPF_CALL_1(bpf_get_socket_uid, struct sk_buff *, skb)
> +{
> +	struct sock *sk = sk_to_full_sk(skb->sk);
> +	kuid_t kuid;
> +
> +	if (!sk || !sk_fullsock(sk))
> +		return overflowuid;
> +	kuid = sock_net_uid(sock_net(sk), sk);
> +	return from_kuid_munged(sock_net(sk)->user_ns, kuid);
> +}
> +
> +static const struct bpf_func_proto bpf_get_socket_uid_proto = {
> +	.func           = bpf_get_socket_uid,
> +	.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)
>  {
> @@ -2648,6 +2666,8 @@ sk_filter_func_proto(enum bpf_func_id func_id)
>  		return &bpf_skb_load_bytes_proto;
>  	case BPF_FUNC_get_socket_cookie:
>  		return &bpf_get_socket_cookie_proto;
> +	case BPF_FUNC_get_socket_uid:
> +		return &bpf_get_socket_uid_proto;
>  	default:
>  		return bpf_base_func_proto(func_id);
>  	}
> @@ -2709,6 +2729,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
>  		return &bpf_skb_under_cgroup_proto;
>  	case BPF_FUNC_get_socket_cookie:
>  		return &bpf_get_socket_cookie_proto;
> +	case BPF_FUNC_get_socket_uid:
> +		return &bpf_get_socket_uid_proto;
>  	default:
>  		return bpf_base_func_proto(func_id);
>  	}
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index a94bdd3..4a2d56d 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -504,7 +504,8 @@ union bpf_attr {
>  	FN(skb_change_head),		\
>  	FN(xdp_adjust_head),		\
>  	FN(probe_read_str),		\
> -	FN(get_socket_cookie),
> +	FN(get_socket_cookie),		\
> +	FN(get_socket_uid),
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
>