linux-kernel - Re: [RFC PATCH bpf-next 00/13] bpf: Introduce BPF namespace

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Message-ID: <CALOAHbA-wRARTaKOrwqvf-rZF1BkNNuEGLgaysY7n6bAqmDRqg@mail.gmail.com>
Date:   Mon, 27 Mar 2023 11:07:46 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Toke Høiland-Jørgensen <toke@...nel.org>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next 00/13] bpf: Introduce BPF namespace

On Sun, Mar 26, 2023 at 6:49 PM Toke Høiland-Jørgensen <toke@...nel.org> wrote:
>
> Yafang Shao <laoar.shao@...il.com> writes:
>
> > Currently only CAP_SYS_ADMIN can iterate BPF object IDs and convert IDs
> > to FDs, that's intended for BPF's security model[1]. Not only does it
> > prevent non-privilidged users from getting other users' bpf program, but
> > also it prevents the user from iterating his own bpf objects.
> >
> > In container environment, some users want to run bpf programs in their
> > containers. These users can run their bpf programs under CAP_BPF and
> > some other specific CAPs, but they can't inspect their bpf programs in a
> > generic way. For example, the bpftool can't be used as it requires
> > CAP_SYS_ADMIN. That is very inconvenient.
> >
> > Without CAP_SYS_ADMIN, the only way to get the information of a bpf object
> > which is not created by the process itself is with SCM_RIGHTS, that
> > requires each processes which created bpf object has to implement a unix
> > domain socket to share the fd of a bpf object between different
> > processes, that is really trivial and troublesome.
> >
> > Hence we need a better mechanism to get bpf object info without
> > CAP_SYS_ADMIN.
> >
> > BPF namespace is introduced in this patchset with an attempt to remove
> > the CAP_SYS_ADMIN requirement. The user can create bpf map, prog and
> > link in a specific bpf namespace, then these bpf objects will not be
> > visible to the users in a different bpf namespace. But these bpf
> > objects are visible to its parent bpf namespace, so the sys admin can
> > still iterate and inspect them.
> >
> > BPF namespace is similar to PID namespace, and the bpf objects are
> > similar to tasks, so BPF namespace is very easy to understand. These
> > patchset only implements BPF namespace for bpf map, prog and link. In the
> > future we may extend it to other bpf objects like btf, bpffs and etc.
>
> May? I think we should cover all of the existing BPF objects from the
> beginning here, or we may miss important interactions that will
> invalidate the whole idea.

This patchset is intended to address iterating bpf IDs and converting
IDs to FDs.  To be more specific, it covers
BPF_{PROG,MAP,LINK}_GET_NEXT_ID and BPF_{PROG,MAP,LINK}_GET_FD_BY_ID.
It should also include BPF_BTF_GET_NEXT_ID and BPF_BTF_GET_FD_BY_ID,
but I don't implement it because I find we can do more wrt BTF, for
example, if we can expose a small amount of BTFs in the vmlinux to
non-root bpf namespace.
But, yes, I should implement BTF ID in this patchset.

> In particular, I'm a little worried about the
> interaction between namespaces and bpffs; what happens if you're in a
> bpf namespace and you try to read a BPF object from a bpffs that belongs
> to a different namespace? Does the operation fail? Is the object hidden
> entirely? Something else?
>

bpffs is a different topic and it can be implemented in later patchsets.
bpffs has its own specific problem even without the bpf namespace.
1. The user can always get the information of a bpf object through its
corresponding pinned file.
In our practice, different container users have different bpffs, and
we allow the container user to bind-mount its bpffs only, so others'
bpffs are invisible.
To make it better with the bpf namespace, I think we can fail the
operation if the pinned file doesn't belong to its bpf namespace. That
said, we will add pinned bpf files into the bpf namespace in the next
step.

2. The user can always iterate bpf objects through progs.debug and maps.debug
progs.debug and maps.debug are debugging purposes only. So I think we
can handle it later.

-- 
Regards
Yafang