net: bpf: Implement bpf iterator for tcp

The bpf iterator for tcp is implemented. Both tcp4 and tcp6
sockets will be traversed. It is up to bpf program to
filter for tcp4 or tcp6 only, or both families of sockets.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200623230805.3987959-1-yhs@fb.com

net/ipv4/tcp_ipv4.c

@@ -2613,6 +2613,74 @@ static int tcp4_seq_show(struct seq_file *seq, void *v)
 	return 0;
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+struct bpf_iter__tcp {
+	__bpf_md_ptr(struct bpf_iter_meta *, meta);
+	__bpf_md_ptr(struct sock_common *, sk_common);
+	uid_t uid __aligned(8);
+};
+
+static int tcp_prog_seq_show(struct bpf_prog *prog, struct bpf_iter_meta *meta,
+			     struct sock_common *sk_common, uid_t uid)
+{
+	struct bpf_iter__tcp ctx;
+
+	meta->seq_num--;  /* skip SEQ_START_TOKEN */
+	ctx.meta = meta;
+	ctx.sk_common = sk_common;
+	ctx.uid = uid;
+	return bpf_iter_run_prog(prog, &ctx);
+}
+
+static int bpf_iter_tcp_seq_show(struct seq_file *seq, void *v)
+{
+	struct bpf_iter_meta meta;
+	struct bpf_prog *prog;
+	struct sock *sk = v;
+	uid_t uid;
+
+	if (v == SEQ_START_TOKEN)
+		return 0;
+
+	if (sk->sk_state == TCP_TIME_WAIT) {
+		uid = 0;
+	} else if (sk->sk_state == TCP_NEW_SYN_RECV) {
+		const struct request_sock *req = v;
+
+		uid = from_kuid_munged(seq_user_ns(seq),
+				       sock_i_uid(req->rsk_listener));
+	} else {
+		uid = from_kuid_munged(seq_user_ns(seq), sock_i_uid(sk));
+	}
+
+	meta.seq = seq;
+	prog = bpf_iter_get_info(&meta, false);
+	return tcp_prog_seq_show(prog, &meta, v, uid);
+}
+
+static void bpf_iter_tcp_seq_stop(struct seq_file *seq, void *v)
+{
+	struct bpf_iter_meta meta;
+	struct bpf_prog *prog;
+
+	if (!v) {
+		meta.seq = seq;
+		prog = bpf_iter_get_info(&meta, true);
+		if (prog)
+			(void)tcp_prog_seq_show(prog, &meta, v, 0);
+	}
+
+	tcp_seq_stop(seq, v);
+}
+
+static const struct seq_operations bpf_iter_tcp_seq_ops = {
+	.show		= bpf_iter_tcp_seq_show,
+	.start		= tcp_seq_start,
+	.next		= tcp_seq_next,
+	.stop		= bpf_iter_tcp_seq_stop,
+};
+#endif
+
 static const struct seq_operations tcp4_seq_ops = {
 	.show		= tcp4_seq_show,
 	.start		= tcp_seq_start,
@@ -2844,8 +2912,63 @@ static struct pernet_operations __net_initdata tcp_sk_ops = {
        .exit_batch = tcp_sk_exit_batch,
 };
 
+#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
+DEFINE_BPF_ITER_FUNC(tcp, struct bpf_iter_meta *meta,
+		     struct sock_common *sk_common, uid_t uid)
+
+static int bpf_iter_init_tcp(void *priv_data)
+{
+	struct tcp_iter_state *st = priv_data;
+	struct tcp_seq_afinfo *afinfo;
+	int ret;
+
+	afinfo = kmalloc(sizeof(*afinfo), GFP_USER | __GFP_NOWARN);
+	if (!afinfo)
+		return -ENOMEM;
+
+	afinfo->family = AF_UNSPEC;
+	st->bpf_seq_afinfo = afinfo;
+	ret = bpf_iter_init_seq_net(priv_data);
+	if (ret)
+		kfree(afinfo);
+	return ret;
+}
+
+static void bpf_iter_fini_tcp(void *priv_data)
+{
+	struct tcp_iter_state *st = priv_data;
+
+	kfree(st->bpf_seq_afinfo);
+	bpf_iter_fini_seq_net(priv_data);
+}
+
+static const struct bpf_iter_reg tcp_reg_info = {
+	.target			= "tcp",
+	.seq_ops		= &bpf_iter_tcp_seq_ops,
+	.init_seq_private	= bpf_iter_init_tcp,
+	.fini_seq_private	= bpf_iter_fini_tcp,
+	.seq_priv_size		= sizeof(struct tcp_iter_state),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__tcp, sk_common),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+};
+
+static void __init bpf_iter_register(void)
+{
+	if (bpf_iter_reg_target(&tcp_reg_info))
+		pr_warn("Warning: could not register bpf iterator tcp\n");
+}
+
+#endif
+
 void __init tcp_v4_init(void)
 {
 	if (register_pernet_subsys(&tcp_sk_ops))
 		panic("Failed to create the TCP control socket.\n");
+
+#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
+	bpf_iter_register();
+#endif
 }