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

[Stanislav Fomichev <sdf@google.com>]

On 03/26, Yafang Shao wrote:
> 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.

Does it essentially mean unpriv bpf? Can I, as a non-root, create
a new bpf namespace and start loading/attaching progs?
Maybe add a paragraph about now vs whatever you're proposing.
Otherwise it's not very clear what's the security story.
(haven't looked at the whole series, so maybe it's answered somewhere else?)

> 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.
> For example, we can allow some of the BTF objects to be used in
> non-init bpf namespace, then the container user can only trace the
> processes running in his container, but can't get the information of
> tasks running in other containers.

> A simple example is introduced into selftests/bpf on how to use the bpf
> namespace.

> Putting bpf map, prog and link into bpf namespace is the first step.
> Let's start with it.

> [1].  
> https://lore.kernel.org/bpf/20200513230355.7858-1-alexei.starovoitov@gmail.com/

> Yafang Shao (13):
>    fork: New clone3 flag for BPF namespace
>    proc_ns: Extend the field type in struct proc_ns_operations to long
>    bpf: Implement bpf namespace
>    bpf: No need to check if id is 0
>    bpf: Make bpf objects id have the same alloc and free pattern
>    bpf: Helpers to alloc and free object id in bpf namespace
>    bpf: Add bpf helper to get bpf object id
>    bpf: Alloc and free bpf_map id in bpf namespace
>    bpf: Alloc and free bpf_prog id in bpf namespace
>    bpf: Alloc and free bpf_link id in bpf namespace
>    bpf: Allow iterating bpf objects with CAP_BPF in bpf namespace
>    bpf: Use bpf_idr_lock array instead
>    selftests/bpf: Add selftest for bpf namespace

>   fs/proc/namespaces.c                      |   4 +
>   include/linux/bpf.h                       |   9 +-
>   include/linux/bpf_namespace.h             |  88 ++++++++++
>   include/linux/nsproxy.h                   |   4 +
>   include/linux/proc_ns.h                   |   3 +-
>   include/linux/user_namespace.h            |   1 +
>   include/uapi/linux/bpf.h                  |   7 +
>   include/uapi/linux/sched.h                |   1 +
>   kernel/bpf/Makefile                       |   1 +
>   kernel/bpf/bpf_namespace.c                | 283  
> ++++++++++++++++++++++++++++++
>   kernel/bpf/offload.c                      |  16 +-
>   kernel/bpf/syscall.c                      | 262  
> ++++++++++-----------------
>   kernel/bpf/task_iter.c                    |  12 ++
>   kernel/fork.c                             |   5 +-
>   kernel/nsproxy.c                          |  19 +-
>   kernel/trace/bpf_trace.c                  |   2 +
>   kernel/ucount.c                           |   1 +
>   tools/bpf/bpftool/skeleton/pid_iter.bpf.c |  13 +-
>   tools/include/uapi/linux/bpf.h            |   7 +
>   tools/testing/selftests/bpf/Makefile      |   3 +-
>   tools/testing/selftests/bpf/test_bpfns.c  |  76 ++++++++
>   21 files changed, 637 insertions(+), 180 deletions(-)
>   create mode 100644 include/linux/bpf_namespace.h
>   create mode 100644 kernel/bpf/bpf_namespace.c
>   create mode 100644 tools/testing/selftests/bpf/test_bpfns.c

> --
> 1.8.3.1