Re: [PATCH net-next v5 2/3] Add a eBPF helper function to retrieve socket uid

From: Chenbo Feng <redacted>

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 <redacted>
---
  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
   */
  #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..a7c25c1 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)
+{
+	kuid_t kuid;
+	struct sock *sk = sk_to_full_sk(skb->sk);