Date:	Fri,  4 Oct 2013 20:20:55 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	pablo@...filter.org
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org
Subject: [PATCH nf-next] netfilter: xtables: lightweight process control group matching

It would be useful e.g. in a server or desktop environment to have
a facility in the notion of fine-grained "per application" or "per
application group" firewall policies. Probably, users in the mobile/
embedded area (e.g. Android based) with different security policy
requirements for application groups could have great benefit from
that as well. For example, with a little bit of configuration effort,
an admin could whitelist well-known applications, and thus block
otherwise unwanted "hard-to-track" applications like [1] from a
user's machine.

Implementation of PID-based matching would not be appropriate
as they frequently change, and child tracking would make that
even more complex and ugly. Cgroups would be a perfect candidate
for accomplishing that as they associate a set of tasks with a
set of parameters for one or more subsystems, in our case the
netfilter subsystem, which, of course, can be combined with other
cgroup subsystems into something more complex.

As mentioned, to overcome this constraint, such processes could
be placed into one or multiple cgroups where different fine-grained
rules can be defined depending on the application scenario, while
e.g. everything else that is not part of that could be dropped (or
vice versa), thus making life harder for unwanted processes to
communicate to the outside world. So, we make use of cgroups here
to track jobs and limit their resources in terms of iptables
policies; in other words, limiting what they are allowed to
communicate.

We have similar cgroup facilities in networking for traffic
classifier, and netprio cgroups. This feature adds a lightweight
cgroup id matching in terms of network security resp. network
traffic isolation as part of netfilter's xtables subsystem.

Minimal, basic usage example (many other iptables options can be
applied obviously):

 1) Configuring cgroups:

  mkdir /sys/fs/cgroup/net_filter
  mount -t cgroup -o net_filter net_filter /sys/fs/cgroup/net_filter
  mkdir /sys/fs/cgroup/net_filter/0
  echo 1 > /sys/fs/cgroup/net_filter/0/net_filter.fwid

 2) Configuring netfilter:

  iptables -A OUTPUT -m cgroup ! --cgroup 1 -j DROP

 3) Running applications:

  ping 208.67.222.222  <pid:1799>
  echo 1799 > /sys/fs/cgroup/net_filter/0/tasks
  64 bytes from 208.67.222.222: icmp_seq=44 ttl=49 time=11.9 ms
  ...

  ping 208.67.220.220  <pid:1804>
  ping: sendmsg: Operation not permitted
  ...
  echo 1804 > /sys/fs/cgroup/net_filter/0/tasks
  64 bytes from 208.67.220.220: icmp_seq=89 ttl=56 time=19.0 ms
  ...

Of course, real-world deployments would make use of cgroups user
space toolsuite, or custom daemons dynamically moving applications
from/to net_filter cgroups.

  [1] http://www.blackhat.com/presentations/bh-europe-06/bh-eu-06-biondi/bh-eu-06-biondi-up.pdf

Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
Cc: Tejun Heo <tj@...nel.org>
Cc: cgroups@...r.kernel.org
---
 Documentation/cgroups/00-INDEX           |   2 +
 Documentation/cgroups/net_filter.txt     |  27 +++++
 include/linux/cgroup_subsys.h            |   5 +
 include/net/netfilter/xt_cgroup.h        |  58 ++++++++++
 include/net/sock.h                       |   3 +
 include/uapi/linux/netfilter/Kbuild      |   1 +
 include/uapi/linux/netfilter/xt_cgroup.h |  11 ++
 net/core/scm.c                           |   2 +
 net/core/sock.c                          |  14 +++
 net/netfilter/Kconfig                    |   8 ++
 net/netfilter/Makefile                   |   1 +
 net/netfilter/xt_cgroup.c                | 182 +++++++++++++++++++++++++++++++
 12 files changed, 314 insertions(+)
 create mode 100644 Documentation/cgroups/net_filter.txt
 create mode 100644 include/net/netfilter/xt_cgroup.h
 create mode 100644 include/uapi/linux/netfilter/xt_cgroup.h
 create mode 100644 net/netfilter/xt_cgroup.c

diff --git a/Documentation/cgroups/00-INDEX b/Documentation/cgroups/00-INDEX
index bc461b6..14424d2 100644
--- a/Documentation/cgroups/00-INDEX
+++ b/Documentation/cgroups/00-INDEX
@@ -20,6 +20,8 @@ memory.txt
 	- Memory Resource Controller; design, accounting, interface, testing.
 net_cls.txt
 	- Network classifier cgroups details and usages.
+net_filter.txt
+	- Network firewalling (netfilter) cgroups details and usages.
 net_prio.txt
 	- Network priority cgroups details and usages.
 resource_counter.txt
diff --git a/Documentation/cgroups/net_filter.txt b/Documentation/cgroups/net_filter.txt
new file mode 100644
index 0000000..0e21822
--- /dev/null
+++ b/Documentation/cgroups/net_filter.txt
@@ -0,0 +1,27 @@
+Netfilter cgroup
+----------------
+
+The netfilter cgroup provides an interface to aggregate jobs
+to a particular netfilter tag, that can be used to apply
+various iptables/netfilter policies for those jobs in order
+to limit resources/abilities for network communication.
+
+Creating a net_filter cgroups instance creates a net_filter.fwid
+file. The value of net_filter.fwid is initialized to 0 on
+default (so only global iptables/netfilter policies apply).
+You can write a unique decimal fwid tag into net_filter.fwid
+file, and use that tag along with iptables' --cgroup option.
+
+Minimal/basic usage example:
+
+1) Configuring cgroup:
+
+ mkdir /sys/fs/cgroup/net_filter
+ mount -t cgroup -o net_filter net_filter /sys/fs/cgroup/net_filter
+ mkdir /sys/fs/cgroup/net_filter/0
+ echo 1 > /sys/fs/cgroup/net_filter/0/net_filter.fwid
+ echo [pid] > /sys/fs/cgroup/net_filter/0/tasks
+
+2) Configuring netfilter:
+
+ iptables -A OUTPUT -m cgroup ! --cgroup 1 -p tcp --dport 80 -j DROP
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index b613ffd..ef58217 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -50,6 +50,11 @@ SUBSYS(net_prio)
 #if IS_SUBSYS_ENABLED(CONFIG_CGROUP_HUGETLB)
 SUBSYS(hugetlb)
 #endif
+
+#if IS_SUBSYS_ENABLED(CONFIG_NETFILTER_XT_MATCH_CGROUP)
+SUBSYS(net_filter)
+#endif
+
 /*
  * DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
  */
diff --git a/include/net/netfilter/xt_cgroup.h b/include/net/netfilter/xt_cgroup.h
new file mode 100644
index 0000000..b2c702f
--- /dev/null
+++ b/include/net/netfilter/xt_cgroup.h
@@ -0,0 +1,58 @@
+#ifndef _XT_CGROUP_H
+#define _XT_CGROUP_H
+
+#include <linux/types.h>
+#include <linux/cgroup.h>
+#include <linux/hardirq.h>
+#include <linux/rcupdate.h>
+
+#if IS_ENABLED(CONFIG_NETFILTER_XT_MATCH_CGROUP)
+struct cgroup_nf_state {
+	struct cgroup_subsys_state css;
+	u32 fwid;
+};
+
+void sock_update_fwid(struct sock *sk);
+
+#if IS_BUILTIN(CONFIG_NETFILTER_XT_MATCH_CGROUP)
+static inline u32 task_fwid(struct task_struct *p)
+{
+	u32 fwid;
+
+	if (in_interrupt())
+		return 0;
+
+	rcu_read_lock();
+	fwid = container_of(task_css(p, net_filter_subsys_id),
+			    struct cgroup_nf_state, css)->fwid;
+	rcu_read_unlock();
+
+	return fwid;
+}
+#elif IS_MODULE(CONFIG_NETFILTER_XT_MATCH_CGROUP)
+static inline u32 task_fwid(struct task_struct *p)
+{
+	struct cgroup_subsys_state *css;
+	u32 fwid = 0;
+
+	if (in_interrupt())
+		return 0;
+
+	rcu_read_lock();
+	css = task_css(p, net_filter_subsys_id);
+	if (css)
+		fwid = container_of(css, struct cgroup_nf_state, css)->fwid;
+	rcu_read_unlock();
+
+	return fwid;
+}
+#endif
+#else /* !CONFIG_NETFILTER_XT_MATCH_CGROUP */
+static inline u32 task_fwid(struct task_struct *p)
+{
+	return 0;
+}
+
+#define sock_update_fwid(sk)
+#endif /* CONFIG_NETFILTER_XT_MATCH_CGROUP */
+#endif /* _XT_CGROUP_H */
diff --git a/include/net/sock.h b/include/net/sock.h
index e3bf213..f7da4b4 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -387,6 +387,9 @@ struct sock {
 #if IS_ENABLED(CONFIG_NETPRIO_CGROUP)
 	__u32			sk_cgrp_prioidx;
 #endif
+#if IS_ENABLED(CONFIG_NETFILTER_XT_MATCH_CGROUP)
+	__u32			sk_cgrp_fwid;
+#endif
 	struct pid		*sk_peer_pid;
 	const struct cred	*sk_peer_cred;
 	long			sk_rcvtimeo;
diff --git a/include/uapi/linux/netfilter/Kbuild b/include/uapi/linux/netfilter/Kbuild
index 1749154..94a4890 100644
--- a/include/uapi/linux/netfilter/Kbuild
+++ b/include/uapi/linux/netfilter/Kbuild
@@ -37,6 +37,7 @@ header-y += xt_TEE.h
 header-y += xt_TPROXY.h
 header-y += xt_addrtype.h
 header-y += xt_bpf.h
+header-y += xt_cgroup.h
 header-y += xt_cluster.h
 header-y += xt_comment.h
 header-y += xt_connbytes.h
diff --git a/include/uapi/linux/netfilter/xt_cgroup.h b/include/uapi/linux/netfilter/xt_cgroup.h
new file mode 100644
index 0000000..43acb7e
--- /dev/null
+++ b/include/uapi/linux/netfilter/xt_cgroup.h
@@ -0,0 +1,11 @@
+#ifndef _UAPI_XT_CGROUP_H
+#define _UAPI_XT_CGROUP_H
+
+#include <linux/types.h>
+
+struct xt_cgroup_info {
+	__u32 id;
+	__u32 invert;
+};
+
+#endif /* _UAPI_XT_CGROUP_H */
diff --git a/net/core/scm.c b/net/core/scm.c
index b442e7e..f08672a 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -36,6 +36,7 @@
 #include <net/sock.h>
 #include <net/compat.h>
 #include <net/scm.h>
+#include <net/netfilter/xt_cgroup.h>
 #include <net/cls_cgroup.h>
 
 
@@ -290,6 +291,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 		/* Bump the usage count and install the file. */
 		sock = sock_from_file(fp[i], &err);
 		if (sock) {
+			sock_update_fwid(sock->sk);
 			sock_update_netprioidx(sock->sk);
 			sock_update_classid(sock->sk);
 		}
diff --git a/net/core/sock.c b/net/core/sock.c
index 2bd9b3f..524a376 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -125,6 +125,7 @@
 #include <linux/skbuff.h>
 #include <net/net_namespace.h>
 #include <net/request_sock.h>
+#include <net/netfilter/xt_cgroup.h>
 #include <net/sock.h>
 #include <linux/net_tstamp.h>
 #include <net/xfrm.h>
@@ -1337,6 +1338,18 @@ void sock_update_netprioidx(struct sock *sk)
 EXPORT_SYMBOL_GPL(sock_update_netprioidx);
 #endif
 
+#if IS_ENABLED(CONFIG_NETFILTER_XT_MATCH_CGROUP)
+void sock_update_fwid(struct sock *sk)
+{
+	u32 fwid;
+
+	fwid = task_fwid(current);
+	if (fwid != sk->sk_cgrp_fwid)
+		sk->sk_cgrp_fwid = fwid;
+}
+EXPORT_SYMBOL(sock_update_fwid);
+#endif
+
 /**
  *	sk_alloc - All socket objects are allocated here
  *	@net: the applicable net namespace
@@ -1363,6 +1376,7 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
 
 		sock_update_classid(sk);
 		sock_update_netprioidx(sk);
+		sock_update_fwid(sk);
 	}
 
 	return sk;
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 6e839b6..d276ff4 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -806,6 +806,14 @@ config NETFILTER_XT_MATCH_BPF
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config NETFILTER_XT_MATCH_CGROUP
+	tristate '"control group" match support'
+	depends on NETFILTER_ADVANCED
+	depends on CGROUPS
+	---help---
+	Socket/process control group matching allows you to match locally
+	generated packets based on which control group processes belong to.
+
 config NETFILTER_XT_MATCH_CLUSTER
 	tristate '"cluster" match support'
 	depends on NF_CONNTRACK
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index c3a0a12..12f014f 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -124,6 +124,7 @@ obj-$(CONFIG_NETFILTER_XT_MATCH_MULTIPORT) += xt_multiport.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_NFACCT) += xt_nfacct.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_OSF) += xt_osf.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_OWNER) += xt_owner.o
+obj-$(CONFIG_NETFILTER_XT_MATCH_CGROUP) += xt_cgroup.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_PHYSDEV) += xt_physdev.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_PKTTYPE) += xt_pkttype.o
 obj-$(CONFIG_NETFILTER_XT_MATCH_POLICY) += xt_policy.o
diff --git a/net/netfilter/xt_cgroup.c b/net/netfilter/xt_cgroup.c
new file mode 100644
index 0000000..86be16d
--- /dev/null
+++ b/net/netfilter/xt_cgroup.c
@@ -0,0 +1,182 @@
+/*
+ * Xtables module to match the process control group.
+ *
+ * Might be used to implement individual "per-application" firewall
+ * policies (in contrast to global policies) based on control groups.
+ *
+ * (C) 2013 Daniel Borkmann <dborkman@...hat.com>
+ * (C) 2013 Thomas Graf <tgraf@...hat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/skbuff.h>
+#include <linux/module.h>
+#include <linux/file.h>
+#include <linux/cgroup.h>
+#include <linux/fdtable.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_cgroup.h>
+#include <net/netfilter/xt_cgroup.h>
+#include <net/sock.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Daniel Borkmann <dborkman@...hat.com>");
+MODULE_DESCRIPTION("Xtables: process control group matching");
+MODULE_ALIAS("ipt_cgroup");
+MODULE_ALIAS("ip6t_cgroup");
+
+static int cgroup_mt_check(const struct xt_mtchk_param *par)
+{
+	struct xt_cgroup_info *info = par->matchinfo;
+
+	if (info->invert & ~1)
+		return -EINVAL;
+
+	return info->id ? 0 : -EINVAL;
+}
+
+static bool
+cgroup_mt(const struct sk_buff *skb, struct xt_action_param *par)
+{
+	const struct xt_cgroup_info *info = par->matchinfo;
+
+	if (skb->sk == NULL)
+		return false;
+
+	return (info->id == skb->sk->sk_cgrp_fwid) ^ info->invert;
+}
+
+static struct xt_match cgroup_mt_reg __read_mostly = {
+	.name       = "cgroup",
+	.revision   = 0,
+	.family     = NFPROTO_UNSPEC,
+	.checkentry = cgroup_mt_check,
+	.match      = cgroup_mt,
+	.matchsize  = sizeof(struct xt_cgroup_info),
+	.me         = THIS_MODULE,
+	.hooks      = (1 << NF_INET_LOCAL_OUT) |
+	              (1 << NF_INET_POST_ROUTING),
+};
+
+static inline struct cgroup_nf_state *
+css_nf_state(struct cgroup_subsys_state *css)
+{
+	return css ? container_of(css, struct cgroup_nf_state, css) : NULL;
+}
+
+static inline struct cgroup_nf_state *task_nf_state(struct task_struct *p)
+{
+	return css_nf_state(task_css(p, net_filter_subsys_id));
+}
+
+static struct cgroup_subsys_state *
+cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
+{
+	struct cgroup_nf_state *cs;
+
+	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
+	if (!cs)
+		return ERR_PTR(-ENOMEM);
+
+	return &cs->css;
+}
+
+static int cgroup_css_online(struct cgroup_subsys_state *css)
+{
+	struct cgroup_nf_state *cs = css_nf_state(css);
+	struct cgroup_nf_state *parent = css_nf_state(css_parent(css));
+
+	if (parent)
+		cs->fwid = parent->fwid;
+
+	return 0;
+}
+
+static void cgroup_css_free(struct cgroup_subsys_state *css)
+{
+	kfree(css_nf_state(css));
+}
+
+static int cgroup_fwid_update(const void *v, struct file *file, unsigned n)
+{
+	int err;
+	struct socket *sock = sock_from_file(file, &err);
+
+	if (sock)
+		sock->sk->sk_cgrp_fwid = (u32)(unsigned long) v;
+
+	return 0;
+}
+
+static u64 cgroup_fwid_read(struct cgroup_subsys_state *css,
+			    struct cftype *cft)
+{
+	return css_nf_state(css)->fwid;
+}
+
+static int cgroup_fwid_write(struct cgroup_subsys_state *css,
+			     struct cftype *cft, u64 id)
+{
+	css_nf_state(css)->fwid = (u32) id;
+
+	return 0;
+}
+
+static void cgroup_attach(struct cgroup_subsys_state *css,
+			  struct cgroup_taskset *tset)
+{
+	struct task_struct *p;
+	void *v;
+
+	cgroup_taskset_for_each(p, css, tset) {
+		task_lock(p);
+		v = (void *)(unsigned long) task_fwid(p);
+		iterate_fd(p->files, 0, cgroup_fwid_update, v);
+		task_unlock(p);
+	}
+}
+
+static struct cftype net_filter_ss_files[] = {
+	{
+		.name		= "fwid",
+		.read_u64	= cgroup_fwid_read,
+		.write_u64	= cgroup_fwid_write,
+	},
+	{ }
+};
+
+struct cgroup_subsys net_filter_subsys = {
+	.name		= "net_filter",
+	.css_alloc	= cgroup_css_alloc,
+	.css_online	= cgroup_css_online,
+	.css_free	= cgroup_css_free,
+	.attach		= cgroup_attach,
+	.subsys_id	= net_filter_subsys_id,
+	.base_cftypes	= net_filter_ss_files,
+	.module		= THIS_MODULE,
+};
+
+static int __init cgroup_mt_init(void)
+{
+	int ret = cgroup_load_subsys(&net_filter_subsys);
+	if (ret)
+		goto out;
+
+	ret = xt_register_match(&cgroup_mt_reg);
+	if (ret)
+		cgroup_unload_subsys(&net_filter_subsys);
+out:
+	return ret;
+}
+
+static void __exit cgroup_mt_exit(void)
+{
+	xt_unregister_match(&cgroup_mt_reg);
+	cgroup_unload_subsys(&net_filter_subsys);
+}
+
+module_init(cgroup_mt_init);
+module_exit(cgroup_mt_exit);
-- 
1.8.3.1

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