[PATCH] bpf: Add bpf_skb_get_sock_comm() helper

[Jiang Yu]

skb distinguished by uid can only recorded to user who consume them.
in many case, skb should been recorded more specific to process who
consume them. E.g, the unexpected large data traffic of illegal process
in metered network.

this helper is used in tracing task comm of the sock to which a skb
belongs.

Signed-off-by: Jiang Yu <jyu.jiang@xxxxxxxx>
---
 include/net/sock.h             |  1 +
 include/uapi/linux/bpf.h       |  1 +
 net/core/filter.c              | 32 ++++++++++++++++++++++++++++++++
 net/core/sock.c                | 20 ++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  1 +
 5 files changed, 55 insertions(+)

diff --git a/include/net/sock.h b/include/net/sock.h
index 064637d1ddf6..9c6e8e61940f 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -519,6 +519,7 @@ struct sock {
 #ifdef CONFIG_BPF_SYSCALL
 	struct bpf_sk_storage __rcu	*sk_bpf_storage;
 #endif
+	char sk_task_com[TASK_COMM_LEN];
 	struct rcu_head		sk_rcu;
 };
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index b134e679e9db..c7f62215a483 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3538,6 +3538,7 @@ union bpf_attr {
 	FN(skc_to_tcp_request_sock),	\
 	FN(skc_to_udp6_sock),		\
 	FN(get_task_stack),		\
+	FN(skb_get_sock_comm),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/net/core/filter.c b/net/core/filter.c
index 7124f0fe6974..972c0bf8e7ca 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4313,6 +4313,36 @@ static const struct bpf_func_proto bpf_get_socket_uid_proto = {
 	.arg1_type      = ARG_PTR_TO_CTX,
 };
 
+BPF_CALL_3(bpf_skb_get_sock_comm,     struct sk_buff *, skb, char *, buf, u32, size)
+{
+	struct sock *sk;
+
+	if (!buf || 0 == size)
+		return -EINVAL;
+
+	sk = sk_to_full_sk(skb->sk);
+	if (!sk || !sk_fullsock(sk))
+		goto err_clear;
+
+	memcpy(buf, sk->sk_task_com, size);
+	buf[size - 1] = 0;
+	return 0;
+
+err_clear:
+	memset(buf, 0, size);
+	buf[size - 1] = 0;
+	return -ENOENT;
+}
+
+const struct bpf_func_proto bpf_skb_get_sock_comm_proto = {
+	.func           = bpf_skb_get_sock_comm,
+	.gpl_only       = false,
+	.ret_type       = RET_INTEGER,
+	.arg1_type      = ARG_PTR_TO_CTX,
+	.arg2_type      = ARG_PTR_TO_MEM,
+	.arg3_type      = ARG_CONST_SIZE,
+};
+
 #define SOCKOPT_CC_REINIT (1 << 0)
 
 static int _bpf_setsockopt(struct sock *sk, int level, int optname,
@@ -6313,6 +6343,8 @@ sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_socket_cookie_proto;
 	case BPF_FUNC_get_socket_uid:
 		return &bpf_get_socket_uid_proto;
+	case BPF_FUNC_skb_get_sock_comm:
+		return &bpf_skb_get_sock_comm_proto;
 	case BPF_FUNC_perf_event_output:
 		return &bpf_skb_event_output_proto;
 	default:
diff --git a/net/core/sock.c b/net/core/sock.c
index d29709e0790d..79d81afa048f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2961,6 +2961,24 @@ void sk_stop_timer(struct sock *sk, struct timer_list* timer)
 }
 EXPORT_SYMBOL(sk_stop_timer);
 
+void sock_init_task_comm(struct sock *sk)
+{
+	struct pid *pid = NULL;
+	struct task_struct *tgid_task = NULL;
+
+	pid = find_get_pid(current->tgid);
+	if (pid) {
+		tgid_task = get_pid_task(pid, PIDTYPE_PID);
+
+		if (tgid_task) {
+			snprintf(sk->sk_task_com, TASK_COMM_LEN, tgid_task->comm);
+			put_task_struct(tgid_task);
+		}
+
+		put_pid(pid);
+	}
+}
+
 void sock_init_data(struct socket *sock, struct sock *sk)
 {
 	sk_init_common(sk);
@@ -3031,6 +3049,8 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 	WRITE_ONCE(sk->sk_pacing_shift, 10);
 	sk->sk_incoming_cpu = -1;
 
+	sock_init_task_comm(sk);
+
 	sk_rx_queue_clear(sk);
 	/*
 	 * Before updating sk_refcnt, we must commit prior changes to memory
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index b134e679e9db..c7f62215a483 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3538,6 +3538,7 @@ union bpf_attr {
 	FN(skc_to_tcp_request_sock),	\
 	FN(skc_to_udp6_sock),		\
 	FN(get_task_stack),		\
+	FN(skb_get_sock_comm),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.25.1