net sched actions: Add support for user cookies

Introduce optional 128-bit action cookie.
Like all other cookie schemes in the networking world (eg in protocols
like http or existing kernel fib protocol field, etc) the idea is to save
user state that when retrieved serves as a correlator. The kernel
_should not_ intepret it.  The user can store whatever they wish in the
128 bits.

Sample exercise(showing variable length use of cookie)

.. create an accept action with cookie a1b2c3d4
sudo $TC actions add action ok index 1 cookie a1b2c3d4

.. dump all gact actions..
sudo $TC -s actions ls action gact

    action order 0: gact action pass
     random type none pass val 0
     index 1 ref 1 bind 0 installed 5 sec used 5 sec
    Action statistics:
    Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
    backlog 0b 0p requeues 0
    cookie a1b2c3d4

.. bind the accept action to a filter..
sudo $TC filter add dev lo parent ffff: protocol ip prio 1 \
u32 match ip dst 127.0.0.1/32 flowid 1:1 action gact index 1

... send some traffic..
$ ping 127.0.0.1 -c 3
PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.020 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.027 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.038 ms
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/act_api.h

@@ -41,6 +41,7 @@ struct tc_action {
 	struct rcu_head			tcfa_rcu;
 	struct gnet_stats_basic_cpu __percpu *cpu_bstats;
 	struct gnet_stats_queue __percpu *cpu_qstats;
+	struct tc_cookie	*act_cookie;
 };
 #define tcf_head	common.tcfa_head
 #define tcf_index	common.tcfa_index

include/net/pkt_cls.h

@@ -515,4 +515,12 @@ struct tc_cls_bpf_offload {
 	u32 gen_flags;
 };
 
+
+/* This structure holds cookie structure that is passed from user
+ * to the kernel for actions and classifiers
+ */
+struct tc_cookie {
+	u8  *data;
+	u32 len;
+};
 #endif

include/uapi/linux/pkt_cls.h

@@ -4,6 +4,8 @@
 #include <linux/types.h>
 #include <linux/pkt_sched.h>
 
+#define TC_COOKIE_MAX_SIZE 16
+
 /* Action attributes */
 enum {
 	TCA_ACT_UNSPEC,
@@ -12,6 +14,7 @@ enum {
 	TCA_ACT_INDEX,
 	TCA_ACT_STATS,
 	TCA_ACT_PAD,
+	TCA_ACT_COOKIE,
 	__TCA_ACT_MAX
 };
 

net/sched/act_api.c

@@ -24,6 +24,7 @@
 #include <net/net_namespace.h>
 #include <net/sock.h>
 #include <net/sch_generic.h>
+#include <net/pkt_cls.h>
 #include <net/act_api.h>
 #include <net/netlink.h>
 
@@ -33,6 +34,12 @@ static void free_tcf(struct rcu_head *head)
 
 	free_percpu(p->cpu_bstats);
 	free_percpu(p->cpu_qstats);
+
+	if (p->act_cookie) {
+		kfree(p->act_cookie->data);
+		kfree(p->act_cookie);
+	}
+
 	kfree(p);
 }
 
@@ -475,6 +482,12 @@ tcf_action_dump_1(struct sk_buff *skb, struct tc_action *a, int bind, int ref)
 		goto nla_put_failure;
 	if (tcf_action_copy_stats(skb, a, 0))
 		goto nla_put_failure;
+	if (a->act_cookie) {
+		if (nla_put(skb, TCA_ACT_COOKIE, a->act_cookie->len,
+			    a->act_cookie->data))
+			goto nla_put_failure;
+	}
+
 	nest = nla_nest_start(skb, TCA_OPTIONS);
 	if (nest == NULL)
 		goto nla_put_failure;
@@ -516,6 +529,22 @@ int tcf_action_dump(struct sk_buff *skb, struct list_head *actions,
 	return err;
 }
 
+int nla_memdup_cookie(struct tc_action *a, struct nlattr **tb)
+{
+	a->act_cookie = kzalloc(sizeof(*a->act_cookie), GFP_KERNEL);
+	if (!a->act_cookie)
+		return -ENOMEM;
+
+	a->act_cookie->data = nla_memdup(tb[TCA_ACT_COOKIE], GFP_KERNEL);
+	if (!a->act_cookie->data) {
+		kfree(a->act_cookie);
+		return -ENOMEM;
+	}
+	a->act_cookie->len = nla_len(tb[TCA_ACT_COOKIE]);
+
+	return 0;
+}
+
 struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
 				    struct nlattr *est, char *name, int ovr,
 				    int bind)
@@ -575,6 +604,22 @@ struct tc_action *tcf_action_init_1(struct net *net, struct nlattr *nla,
 	if (err < 0)
 		goto err_mod;
 
+	if (tb[TCA_ACT_COOKIE]) {
+		int cklen = nla_len(tb[TCA_ACT_COOKIE]);
+
+		if (cklen > TC_COOKIE_MAX_SIZE) {
+			err = -EINVAL;
+			tcf_hash_release(a, bind);
+			goto err_mod;
+		}
+
+		err = nla_memdup_cookie(a, tb);
+		if (err < 0) {
+			tcf_hash_release(a, bind);
+			goto err_mod;
+		}
+	}
+
 	/* module count goes up only when brand new policy is created
 	 * if it exists and is only bound to in a_o->init() then
 	 * ACT_P_CREATED is not returned (a zero is).