[RFC Patch v6 5/5] net_sched: Introduce helper bpf_skb_tc_classify()

[Cong Wang <xiyou.wangcong@gmail.com>]

From: Cong Wang <cong.wang@bytedance.com>

Introduce an eBPF helper function bpf_skb_tc_classify() to reuse exising
TC filters on *any* Qdisc to classify the skb.

Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
 include/uapi/linux/bpf.h |  1 +
 net/core/filter.c        | 17 +++++++++-
 net/sched/cls_api.c      | 69 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c21fd1f189bc..7ed04736c4e4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5650,6 +5650,7 @@ union bpf_attr {
 	FN(tcp_raw_check_syncookie_ipv6),	\
 	FN(ktime_get_tai_ns),		\
 	FN(user_ringbuf_drain),		\
+	FN(skb_tc_classify),		\
 	/* */
 
 /* 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 7a271b77a2cc..d1ed60114794 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7926,6 +7926,21 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	}
 }
 
+const struct bpf_func_proto bpf_skb_tc_classify_proto __weak;
+
+static const struct bpf_func_proto *
+tc_qdisc_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
+{
+	switch (func_id) {
+#ifdef CONFIG_NET_CLS_ACT
+	case BPF_FUNC_skb_tc_classify:
+		return &bpf_skb_tc_classify_proto;
+#endif
+	default:
+		return tc_cls_act_func_proto(func_id, prog);
+	}
+}
+
 static const struct bpf_func_proto *
 xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -10656,7 +10671,7 @@ const struct bpf_prog_ops tc_cls_act_prog_ops = {
 };
 
 const struct bpf_verifier_ops tc_qdisc_verifier_ops = {
-	.get_func_proto		= tc_cls_act_func_proto,
+	.get_func_proto		= tc_qdisc_func_proto,
 	.is_valid_access	= tc_cls_act_is_valid_access,
 	.convert_ctx_access	= tc_cls_act_convert_ctx_access,
 	.gen_prologue		= tc_cls_act_prologue,
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 50566db45949..64470a8947b1 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -22,6 +22,7 @@
 #include <linux/idr.h>
 #include <linux/jhash.h>
 #include <linux/rculist.h>
+#include <linux/filter.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 #include <net/netlink.h>
@@ -1655,6 +1656,74 @@ int tcf_classify(struct sk_buff *skb,
 }
 EXPORT_SYMBOL(tcf_classify);
 
+#ifdef CONFIG_BPF_SYSCALL
+BPF_CALL_3(bpf_skb_tc_classify, struct sk_buff *, skb, int, ifindex, u32, handle)
+{
+	struct net *net = dev_net(skb->dev);
+	const struct Qdisc_class_ops *cops;
+	struct tcf_result res = {};
+	struct tcf_block *block;
+	struct tcf_chain *chain;
+	struct net_device *dev;
+	unsigned long cl = 0;
+	struct Qdisc *q;
+	int result;
+
+	rcu_read_lock();
+	dev = dev_get_by_index_rcu(net, ifindex);
+	if (!dev)
+		goto out;
+	q = qdisc_lookup_rcu(dev, handle);
+	if (!q)
+		goto out;
+
+	cops = q->ops->cl_ops;
+	if (!cops)
+		goto out;
+	if (!cops->tcf_block)
+		goto out;
+	if (TC_H_MIN(handle)) {
+		cl = cops->find(q, handle);
+		if (cl == 0)
+			goto out;
+	}
+	block = cops->tcf_block(q, cl, NULL);
+	if (!block)
+		goto out;
+
+	for (chain = tcf_get_next_chain(block, NULL);
+	     chain;
+	     chain = tcf_get_next_chain(block, chain)) {
+		struct tcf_proto *tp;
+
+		result = tcf_classify(skb, NULL, tp, &res, false);
+		if (result  >= 0) {
+			switch (result) {
+			case TC_ACT_QUEUED:
+			case TC_ACT_STOLEN:
+			case TC_ACT_TRAP:
+				fallthrough;
+			case TC_ACT_SHOT:
+				rcu_read_unlock();
+				return 0;
+			}
+		}
+	}
+out:
+	rcu_read_unlock();
+	return res.class;
+}
+
+const struct bpf_func_proto bpf_skb_tc_classify_proto = {
+	.func		= bpf_skb_tc_classify,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+};
+#endif
+
 struct tcf_chain_info {
 	struct tcf_proto __rcu **pprev;
 	struct tcf_proto __rcu *next;
-- 
2.34.1