On 10/18/2013 03:28 PM, Daniel Borkmann wrote:
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. 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 own custom policy daemons dynamically moving applications from/to various net_filter cgroups. Design considerations appendix: Based on the discussion from [2], [3], it seems the best tradeoff imho to make this a subsystem, here's why: netfilter is a large enough and ubiquitous subsystem, meaning it is not somewhere in a niche, and enabled/shipped on most machines. It is true that the descision making on fwid is "outsourced" to netfilter itself, but that does not necessarily need to be considered as a bad thing to delegate and reuse as much as possible. The matching performance in the critical path is just a simple comparison of fwid tags, nothing more, thus resulting in a good performance suited for high-speed networking. Moreover, by simply transfering fwids between user- and kernel space, we can have the ruleset as packed as possible, giving an optimal footprint for large rulesets using this feature. The alternative draft that we have proposed in [3] comes at the cost of exposing some of the cgroups internals outside of cgroups to make it work, at least a higher memory footprint for transferal of rules and even worse a lower performance as more work needs to be done in the matching critical path, that is traversing all cgroups a task belongs to to find the one of our interest. Moreover, from the usability point of view, it seems less intuitive, rather more confusing than the approach presented here. Therefore, I consider this design the better and less intrusive tradeoff to go with.
As I've provided a code proposal for both variants and a design discussion/conclusion, are you d'accord with this patch Tejun?
[1] http://www.blackhat.com/presentations/bh-europe-06/bh-eu-06-biondi/bh-eu-06-biondi-up.pdf [2] http://patchwork.ozlabs.org/patch/280687/ [3] http://patchwork.ozlabs.org/patch/282477/ Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: cgroups@xxxxxxxxxxxxxxx --- v1->v2: - Updated commit message, rebased - Applied Gao Feng's feedback from [2] Note: iptables part is still available in http://patchwork.ozlabs.org/patch/280690/ 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 | 177 +++++++++++++++++++++++++++++++ 12 files changed, 309 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..22759e4 --- /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..249c7ee --- /dev/null +++ b/net/netfilter/xt_cgroup.c @@ -0,0 +1,177 @@ +/* + * 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@xxxxxxxxxx> + * (C) 2013 Thomas Graf <tgraf@xxxxxxxxxx> + * + * 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@xxxxxxxxxx>"); +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 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 cgroup_nf_state *cs = css_nf_state(css); + void *v = (void *)(unsigned long) cs->fwid; + struct task_struct *p; + + cgroup_taskset_for_each(p, css, tset) { + task_lock(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);
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