BACKPORT: UPSTREAM: Add a eBPF helper function to retrieve socket uid

Cherry-pick from commit 6acc5c2910

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Bug: 30950746
Change-Id: Idc00947ccfdd4e9f2214ffc4178d701cd9ead0ac

tools/include/uapi/linux/bpf.h

@@ -466,6 +466,14 @@ enum bpf_func_id {
 	 */
 	BPF_FUNC_get_socket_cookie,
 
+	/**
+	 * 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 overflowuid if failed.
+	 */
+	BPF_FUNC_get_socket_uid,
+
 	__BPF_FUNC_MAX_ID,
 };