Re: [PATCH bpf-next 0/4] sys_bpf() access control via /dev/bpf

[Stanislav Fomichev <sdf@fomichev.me>]

On 06/25, Song Liu wrote:
> Currently, most access to sys_bpf() is limited to root. However, there are
> use cases that would benefit from non-privileged use of sys_bpf(), e.g.
> systemd.
> 
> This set introduces a new model to control the access to sys_bpf(). A
> special device, /dev/bpf, is introduced to manage access to sys_bpf().
> Users with access to open /dev/bpf will be able to access most of
> sys_bpf() features. The use can get access to sys_bpf() by opening /dev/bpf
> and use ioctl to get/put permission.
> 
> The permission to access sys_bpf() is marked by bit TASK_BPF_FLAG_PERMITTED
> in task_struct. During fork(), child will not inherit this bit.
2c: if we are going to have an fd, I'd vote for a proper fd based access
checks instead of a per-task flag, so we can do:
	ioctl(fd, BPF_MAP_CREATE, uattr, sizeof(uattr))

(and pass this fd around)

I do understand that it breaks current assumptions that libbpf has,
but maybe we can extend _xattr variants to accept optinal fd (and try
to fallback to sysctl if it's absent/not working)?

> libbpf APIs libbpf_[get|put]_bpf_permission() are added to help get and
> put the permission. bpftool is updated to use these APIs.
> 
> Song Liu (4):
>   bpf: unprivileged BPF access via /dev/bpf
>   bpf: sync tools/include/uapi/linux/bpf.h
>   libbpf: add libbpf_[get|put]_bpf_permission()
>   bpftool: use libbpf_[get|put]_bpf_permission()
> 
>  Documentation/ioctl/ioctl-number.txt |  1 +
>  include/linux/bpf.h                  | 12 +++++
>  include/linux/sched.h                |  8 ++++
>  include/uapi/linux/bpf.h             |  5 ++
>  kernel/bpf/arraymap.c                |  2 +-
>  kernel/bpf/cgroup.c                  |  2 +-
>  kernel/bpf/core.c                    |  4 +-
>  kernel/bpf/cpumap.c                  |  2 +-
>  kernel/bpf/devmap.c                  |  2 +-
>  kernel/bpf/hashtab.c                 |  4 +-
>  kernel/bpf/lpm_trie.c                |  2 +-
>  kernel/bpf/offload.c                 |  2 +-
>  kernel/bpf/queue_stack_maps.c        |  2 +-
>  kernel/bpf/reuseport_array.c         |  2 +-
>  kernel/bpf/stackmap.c                |  2 +-
>  kernel/bpf/syscall.c                 | 72 +++++++++++++++++++++-------
>  kernel/bpf/verifier.c                |  2 +-
>  kernel/bpf/xskmap.c                  |  2 +-
>  kernel/fork.c                        |  4 ++
>  net/core/filter.c                    |  6 +--
>  tools/bpf/bpftool/feature.c          |  2 +-
>  tools/bpf/bpftool/main.c             |  5 ++
>  tools/include/uapi/linux/bpf.h       |  5 ++
>  tools/lib/bpf/libbpf.c               | 54 +++++++++++++++++++++
>  tools/lib/bpf/libbpf.h               |  7 +++
>  tools/lib/bpf/libbpf.map             |  2 +
>  26 files changed, 178 insertions(+), 35 deletions(-)
> 
> --
> 2.17.1