Re: [PATCH net-next 2/2] Add a eBPF helper function to retrieve socket uid

[Daniel Borkmann]

On 02/02/2017 09:59 PM, Chenbo Feng wrote:

From: Chenbo Feng <fe...@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.

Signed-off-by: Chenbo Feng <chenbofeng.ker...@gmail.com>
---
  include/linux/bpf.h      |  1 +
  include/uapi/linux/bpf.h |  9 ++++++++-
  net/core/filter.c        | 19 +++++++++++++++++++
  3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 3f2e0af28c6e..c775ca4678b7 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -350,6 +350,7 @@ 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;
+extern const struct bpf_func_proto bpf_get_socket_uid_proto;

Likewise, no need to add it here.

  /* Shared helpers among cBPF and eBPF. */
  void bpf_user_rnd_init_once(void);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 62ee5fab08e5..dad4dc7aca49 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -436,6 +436,12 @@ 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
   */
  #define __BPF_FUNC_MAPPER(FN)         \
        FN(unspec),                     \
@@ -483,7 +489,8 @@ union bpf_attr {
        FN(get_numa_node_id),           \
        FN(skb_change_head),            \
        FN(xdp_adjust_head),            \
-       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 913b14d3b484..bc36ed72551f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2610,6 +2610,23 @@ 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;
+       kuid_t kuid;

Nit: already init them above.

+       sk = skb->sk;
+       kuid = sock_net_uid(dev_net(skb->dev), sk);

Don't you need to test for fullsock? Do you mean something like below?

struct sock *sk = skb->sk;
kuid_t kuid = sock_net_uid(net, sk && sk_fullsock(sk) ?
                           sk : NULL);

+       return (u32)kuid.val;
+}
+
+const struct bpf_func_proto bpf_get_socket_uid_proto = {

static ...

+       .func           = bpf_get_socket_uid,
+       .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)
  {
@@ -2635,6 +2652,8 @@ sk_filter_func_proto(enum bpf_func_id func_id)
                        return bpf_get_trace_printk_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 NULL;
        }