Re: [PATCH bpf-next] BPF: helpers: New helper to obtain namespace data from current task

[Carlos Neira <cneirabustos@gmail.com>]

Yes, you are right. I'll resubmit the patch with those corrections.
Thanks a lot for catching this. 

Thu, Aug 09, 2018 at 03:46:53PM +0200, Jesper Dangaard Brouer wrote:
> On Thu,  9 Aug 2018 09:18:00 -0400
> Carlos Neira <cneirabustos@gmail.com> wrote:
> 
> > From: cneira <cneirabustos@gmail.com>
> > 
> > This helper obtains the active namespace from current and returns pid, tgid,
> > device and namespace id as seen from that namespace, allowing to instrument
> > a process inside a container.
> > Device is read from /proc/self/ns/pid, as in the future it's possible that
> > different pid_ns files may belong to different devices, according
> > to the discussion between Eric Biederman and Yonghong in 2017 linux plumbers
> > conference.
> > 
> > Currently bpf_get_current_pid_tgid(), is used to do pid filtering in bcc's
> > scripts but this helper returns the pid as seen by the root namespace which is
> > fine when a bcc script is not executed inside a container.
> > When the process of interest is inside a container, pid filtering will not work
> > if bpf_get_current_pid_tgid() is used. This helper addresses this limitation
> > returning the pid as it's seen by the current namespace where the script is
> > executing.
> > 
> > This helper has the same use cases as bpf_get_current_pid_tgid() as it can be
> > used to do pid filtering even inside a container.
> > 
> > For example a bcc script using bpf_get_current_pid_tgid() (tools/funccount.py):
> > 
> > 	u32 pid = bpf_get_current_pid_tgid() >> 32;
> > 	if (pid != <pid_arg_passed_in>)
> > 		return 0;
> > 
> > Could be modified to use bpf_get_current_pidns_info() as follows:
> > 
> > 	struct bpf_pidns pidns;
> > 	bpf_get_current_pid_tgid(&pidns, sizeof(struct bpf_pidns));
>         ^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Shouldn't this be:
>         bpf_get_current_pidns_info(...)
> 
> > 	u32 pid = pidns.tgid;
> > 	u32 nsid = pidns.nsid;
> > 	if ((pid != <pid_arg_passed_in>) && (nsid != <nsid_arg_passed_in>))
> > 		return 0;
> > 
> 
> [...]
> 
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index dd5758dc35d3..031e7d9dba09 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -2113,6 +2113,18 @@ union bpf_attr {
> >   *		the shared data.
> >   *	Return
> >   *		Pointer to the local storage area.
> > + *
> > + * int bpf_get_current_pidns(struct bpf_pidns_info *pidns, u32 size_of_pidns)
> 
> Should this be:
>           bpf_get_current_pidns_info(...)
> 
> > + *	Description
> > + *		Copies into *pidns* pid, namespace id and tgid as seen by the
> > + *		current namespace and also device from /proc/self/ns/pid.
> > + *		*size_of_pidns* must be the size of *pidns*
> > + *
> > + *		This helper is used when pid filtering is needed inside a
> > + *		container as bpf_get_current_tgid() helper returns always the
> > + *		pid id as seen by the root namespace.
> > + *	Return
> > + *		0 on success -EINVAL on error.
> >   */
> >  #define __BPF_FUNC_MAPPER(FN)		\
> >  	FN(unspec),			\
> > @@ -2196,7 +2208,8 @@ union bpf_attr {
> >  	FN(rc_keydown),			\
> >  	FN(skb_cgroup_id),		\
> >  	FN(get_current_cgroup_id),	\
> > -	FN(get_local_storage),
> > +	FN(get_local_storage),		\
> > +	FN(get_current_pidns_info),
> 
> -- 
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer