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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. Blocking is just one example, but it is not limited to that, meaning we can have much different scenarios/policies that netfilter allows us than just blocking, e.g. fine grained settings where applications are allowed to connect/send traffic to, application traffic marking/conntracking, application-specific packet mangling, and so on. 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 if needed. 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, tracking, etc what they are allowed to communicate. In our case we're working on outgoing traffic based on which local socket that originated from. Also, one doesn't even need to have an a-prio knowledge of the application internals regarding their particular use of ports or protocols. Matching is *extremly* lightweight as we just test for the sk_classid marker of sockets, originating from net_cls. net_cls and netfilter do not contradict each other; in fact, each construct can live as standalone or they can be used in combination with each other, which is perfectly fine, plus it serves Tejun's requirement to not introduce a new cgroups subsystem. Through this, we result in a very minimal and efficient module, and don't add anything except netfilter code. One possible, minimal usage example (many other iptables options can be applied obviously): 1) Configuring cgroups if not already done, e.g.: mkdir /sys/fs/cgroup/net_cls mount -t cgroup -o net_cls net_cls /sys/fs/cgroup/net_cls mkdir /sys/fs/cgroup/net_cls/0 echo 1 > /sys/fs/cgroup/net_cls/0/net_cls.classid (resp. a real flow handle id for tc) 2) Configuring netfilter (iptables-nftables), e.g.: iptables -A OUTPUT -m cgroup ! --cgroup 1 -j DROP 3) Running applications, e.g.: ping 208.67.222.222 <pid:1799> echo 1799 > /sys/fs/cgroup/net_cls/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_cls/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 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@redhat.com> Cc: Tejun Heo <tj@kernel.org> Cc: cgroups@vger.kernel.org Acked-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> |
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