Re: [RFC] [PATCH bpf-next 1/1] bpf: Add a BPF helper for getting the cgroup path of current task

[xufeng zhang]

在 2021/5/13 上午6:55, Alexei Starovoitov 写道:
> On Wed, May 12, 2021 at 05:58:23PM +0800, Xufeng Zhang wrote:
> > To implement security rules for application containers by utilizing
> > bpf LSM, the container to which the current running task belongs need
> > to be known in bpf context. Think about this scenario: kubernetes
> > schedules a pod into one host, before the application container can run,
> > the security rules for this application need to be loaded into bpf
> > maps firstly, so that LSM bpf programs can make decisions based on
> > this rule maps.
> >
> > However, there is no effective bpf helper to achieve this goal,
> > especially for cgroup v1. In the above case, the only available information
> > from user side is container-id, and the cgroup path for this container
> > is certain based on container-id, so in order to make a bridge between
> > user side and bpf programs, bpf programs also need to know the current
> > cgroup path of running task.
> ...
> > +#ifdef CONFIG_CGROUPS
> > +BPF_CALL_2(bpf_get_current_cpuset_cgroup_path, char *, buf, u32, buf_len)
> > +{
> > +	struct cgroup_subsys_state *css;
> > +	int retval;
> > +
> > +	css = task_get_css(current, cpuset_cgrp_id);
> > +	retval = cgroup_path_ns(css->cgroup, buf, buf_len, &init_cgroup_ns);
> > +	css_put(css);
> > +	if (retval >= buf_len)
> > +		retval = -ENAMETOOLONG;
> Manipulating string path to check the hierarchy will be difficult to do
> inside bpf prog. It seems to me this helper will be useful only for
> simplest cgroup setups where there is no additional cgroup nesting
> within containers.
> Have you looked at *ancestor_cgroup_id and *cgroup_id helpers?
> They're a bit more flexible when dealing with hierarchy and
> can be used to achieve the same correlation between kernel and user cgroup ids.


KP,

do you have any suggestion?

what I am thinking is the internal kernel object(cgroup id or ns.inum) 
is not so user friendly, we can get the container-context from them for 
tracing scenario, but not for LSM blocking cases, I'm not sure how 
Google internally resolve similar issue.


Thanks!

Xufeng