pkt_sched: Control group classifier

The classifier should cover the most common use case and will work
without any special configuration.

The principle of the classifier is to directly access the
task_struct via get_current(). In order for this to work,
classification requests from softirqs must be ignored. This is
not a problem because the vast majority of packets in softirq
context are not assigned to a task anyway. For this to work, a
mechanism is needed to trace softirq context. 

This repost goes back to the method of relying on the number of
nested bh disable calls for the sake of not adding too much
complexity and the option to come up with something more reliable
if actually needed.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/cgroup_subsys.h

@@ -54,3 +54,9 @@ SUBSYS(freezer)
 #endif
 
 /* */
+
+#ifdef CONFIG_NET_CLS_CGROUP
+SUBSYS(net_cls)
+#endif
+
+/* */

include/linux/pkt_cls.h

@@ -394,6 +394,20 @@ enum
 
 #define TCA_BASIC_MAX (__TCA_BASIC_MAX - 1)
 
+
+/* Cgroup classifier */
+
+enum
+{
+	TCA_CGROUP_UNSPEC,
+	TCA_CGROUP_ACT,
+	TCA_CGROUP_POLICE,
+	TCA_CGROUP_EMATCHES,
+	__TCA_CGROUP_MAX,
+};
+
+#define TCA_CGROUP_MAX (__TCA_CGROUP_MAX - 1)
+
 /* Extended Matches */
 
 struct tcf_ematch_tree_hdr

net/sched/Kconfig

@@ -316,6 +316,17 @@ config NET_CLS_FLOW
 	  To compile this code as a module, choose M here: the
 	  module will be called cls_flow.
 
+config NET_CLS_CGROUP
+	bool "Control Group Classifier"
+	select NET_CLS
+	depends on CGROUPS
+	---help---
+	  Say Y here if you want to classify packets based on the control
+	  cgroup of their process.
+
+	  To compile this code as a module, choose M here: the
+	  module will be called cls_cgroup.
+
 config NET_EMATCH
 	bool "Extended Matches"
 	select NET_CLS

net/sched/Makefile

@@ -38,6 +38,7 @@ obj-$(CONFIG_NET_CLS_TCINDEX)	+= cls_tcindex.o
 obj-$(CONFIG_NET_CLS_RSVP6)	+= cls_rsvp6.o
 obj-$(CONFIG_NET_CLS_BASIC)	+= cls_basic.o
 obj-$(CONFIG_NET_CLS_FLOW)	+= cls_flow.o
+obj-$(CONFIG_NET_CLS_CGROUP)	+= cls_cgroup.o
 obj-$(CONFIG_NET_EMATCH)	+= ematch.o
 obj-$(CONFIG_NET_EMATCH_CMP)	+= em_cmp.o
 obj-$(CONFIG_NET_EMATCH_NBYTE)	+= em_nbyte.o

net/sched/cls_cgroup.c

+/*
+ * net/sched/cls_cgroup.c	Control Group Classifier
+ *
+ *		This program is free software; you can redistribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ * Authors:	Thomas Graf <tgraf@suug.ch>
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <linux/cgroup.h>
+#include <net/rtnetlink.h>
+#include <net/pkt_cls.h>
+
+struct cgroup_cls_state
+{
+	struct cgroup_subsys_state css;
+	u32 classid;
+};
+
+static inline struct cgroup_cls_state *net_cls_state(struct cgroup *cgrp)
+{
+	return (struct cgroup_cls_state *)
+		cgroup_subsys_state(cgrp, net_cls_subsys_id);
+}
+
+static struct cgroup_subsys_state *cgrp_create(struct cgroup_subsys *ss,
+						 struct cgroup *cgrp)
+{
+	struct cgroup_cls_state *cs;
+
+	if (!(cs = kzalloc(sizeof(*cs), GFP_KERNEL)))
+		return ERR_PTR(-ENOMEM);
+
+	if (cgrp->parent)
+		cs->classid = net_cls_state(cgrp->parent)->classid;
+
+	return &cs->css;
+}
+
+static void cgrp_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
+{
+	kfree(ss);
+}
+
+static u64 read_classid(struct cgroup *cgrp, struct cftype *cft)
+{
+	return net_cls_state(cgrp)->classid;
+}
+
+static int write_classid(struct cgroup *cgrp, struct cftype *cft, u64 value)
+{
+	if (!cgroup_lock_live_group(cgrp))
+		return -ENODEV;
+
+	net_cls_state(cgrp)->classid = (u32) value;
+
+	cgroup_unlock();
+
+	return 0;
+}
+
+static struct cftype ss_files[] = {
+	{
+		.name = "classid",
+		.read_u64 = read_classid,
+		.write_u64 = write_classid,
+	},
+};
+
+static int cgrp_populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
+{
+	return cgroup_add_files(cgrp, ss, ss_files, ARRAY_SIZE(ss_files));
+}
+
+struct cgroup_subsys net_cls_subsys = {
+	.name		= "net_cls",
+	.create		= cgrp_create,
+	.destroy	= cgrp_destroy,
+	.populate	= cgrp_populate,
+	.subsys_id	= net_cls_subsys_id,
+};
+
+struct cls_cgroup_head
+{
+	u32			handle;
+	struct tcf_exts		exts;
+	struct tcf_ematch_tree	ematches;
+};
+
+static int cls_cgroup_classify(struct sk_buff *skb, struct tcf_proto *tp,
+			       struct tcf_result *res)
+{
+	struct cls_cgroup_head *head = tp->root;
+	struct cgroup_cls_state *cs;
+	int ret = 0;
+
+	/*
+	 * Due to the nature of the classifier it is required to ignore all
+	 * packets originating from softirq context as accessing `current'
+	 * would lead to false results.
+	 *
+	 * This test assumes that all callers of dev_queue_xmit() explicitely
+	 * disable bh. Knowing this, it is possible to detect softirq based
+	 * calls by looking at the number of nested bh disable calls because
+	 * softirqs always disables bh.
+	 */
+	if (softirq_count() != SOFTIRQ_OFFSET)
+		return -1;
+
+	rcu_read_lock();
+	cs = (struct cgroup_cls_state *) task_subsys_state(current,
+							   net_cls_subsys_id);
+	if (cs->classid && tcf_em_tree_match(skb, &head->ematches, NULL)) {
+		res->classid = cs->classid;
+		res->class = 0;
+		ret = tcf_exts_exec(skb, &head->exts, res);
+	} else
+		ret = -1;
+
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static unsigned long cls_cgroup_get(struct tcf_proto *tp, u32 handle)
+{
+	return 0UL;
+}
+
+static void cls_cgroup_put(struct tcf_proto *tp, unsigned long f)
+{
+}
+
+static int cls_cgroup_init(struct tcf_proto *tp)
+{
+	return 0;
+}
+
+static const struct tcf_ext_map cgroup_ext_map = {
+	.action = TCA_CGROUP_ACT,
+	.police = TCA_CGROUP_POLICE,
+};
+
+static const struct nla_policy cgroup_policy[TCA_CGROUP_MAX + 1] = {
+	[TCA_CGROUP_EMATCHES]	= { .type = NLA_NESTED },
+};
+
+static int cls_cgroup_change(struct tcf_proto *tp, unsigned long base,
+			     u32 handle, struct nlattr **tca,
+			     unsigned long *arg)
+{
+	struct nlattr *tb[TCA_CGROUP_MAX+1];
+	struct cls_cgroup_head *head = tp->root;
+	struct tcf_ematch_tree t;
+	struct tcf_exts e;
+	int err;
+
+	if (head == NULL) {
+		if (!handle)
+			return -EINVAL;
+
+		head = kzalloc(sizeof(*head), GFP_KERNEL);
+		if (head == NULL)
+			return -ENOBUFS;
+
+		head->handle = handle;
+
+		tcf_tree_lock(tp);
+		tp->root = head;
+		tcf_tree_unlock(tp);
+	}
+
+	if (handle != head->handle)
+		return -ENOENT;
+
+	err = nla_parse_nested(tb, TCA_CGROUP_MAX, tca[TCA_OPTIONS],
+			       cgroup_policy);
+	if (err < 0)
+		return err;
+
+	err = tcf_exts_validate(tp, tb, tca[TCA_RATE], &e, &cgroup_ext_map);
+	if (err < 0)
+		return err;
+
+	err = tcf_em_tree_validate(tp, tb[TCA_CGROUP_EMATCHES], &t);
+	if (err < 0)
+		return err;
+
+	tcf_exts_change(tp, &head->exts, &e);
+	tcf_em_tree_change(tp, &head->ematches, &t);
+
+	return 0;
+}
+
+static void cls_cgroup_destroy(struct tcf_proto *tp)
+{
+	struct cls_cgroup_head *head;
+
+	head = (struct cls_cgroup_head *)xchg(&tp->root, NULL);
+
+	if (head) {
+		tcf_exts_destroy(tp, &head->exts);
+		tcf_em_tree_destroy(tp, &head->ematches);
+		kfree(head);
+	}
+}
+
+static int cls_cgroup_delete(struct tcf_proto *tp, unsigned long arg)
+{
+	return -EOPNOTSUPP;
+}
+
+static void cls_cgroup_walk(struct tcf_proto *tp, struct tcf_walker *arg)
+{
+	struct cls_cgroup_head *head = tp->root;
+
+	if (arg->count < arg->skip)
+		goto skip;
+
+	if (arg->fn(tp, (unsigned long) head, arg) < 0) {
+		arg->stop = 1;
+		return;
+	}
+skip:
+	arg->count++;
+}
+
+static int cls_cgroup_dump(struct tcf_proto *tp, unsigned long fh,
+			   struct sk_buff *skb, struct tcmsg *t)
+{
+	struct cls_cgroup_head *head = tp->root;
+	unsigned char *b = skb_tail_pointer(skb);
+	struct nlattr *nest;
+
+	t->tcm_handle = head->handle;
+
+	nest = nla_nest_start(skb, TCA_OPTIONS);
+	if (nest == NULL)
+		goto nla_put_failure;
+
+	if (tcf_exts_dump(skb, &head->exts, &cgroup_ext_map) < 0 ||
+	    tcf_em_tree_dump(skb, &head->ematches, TCA_CGROUP_EMATCHES) < 0)
+		goto nla_put_failure;
+
+	nla_nest_end(skb, nest);
+
+	if (tcf_exts_dump_stats(skb, &head->exts, &cgroup_ext_map) < 0)
+		goto nla_put_failure;
+
+	return skb->len;
+
+nla_put_failure:
+	nlmsg_trim(skb, b);
+	return -1;
+}
+
+static struct tcf_proto_ops cls_cgroup_ops __read_mostly = {
+	.kind		=	"cgroup",
+	.init		=	cls_cgroup_init,
+	.change		=	cls_cgroup_change,
+	.classify	=	cls_cgroup_classify,
+	.destroy	=	cls_cgroup_destroy,
+	.get		=	cls_cgroup_get,
+	.put		=	cls_cgroup_put,
+	.delete		=	cls_cgroup_delete,
+	.walk		=	cls_cgroup_walk,
+	.dump		=	cls_cgroup_dump,
+	.owner		=	THIS_MODULE,
+};
+
+static int __init init_cgroup_cls(void)
+{
+	return register_tcf_proto_ops(&cls_cgroup_ops);
+}
+
+static void __exit exit_cgroup_cls(void)
+{
+	unregister_tcf_proto_ops(&cls_cgroup_ops);
+}
+
+module_init(init_cgroup_cls);
+module_exit(exit_cgroup_cls);
+MODULE_LICENSE("GPL");