linux-kernel - Re: [PATCH v2 4/4] bpf,lsm: Allow editing capabilities in BPF-LSM hooks

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Date: Sun, 9 Jun 2024 20:18:48 -0400
From: Paul Moore <paul@...l-moore.com>
To: Jonathan Calmels <jcalmels@...0.net>
Cc: brauner@...nel.org, ebiederm@...ssion.com, 
	Jonathan Corbet <corbet@....net>, James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
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Subject: Re: [PATCH v2 4/4] bpf,lsm: Allow editing capabilities in BPF-LSM hooks

On Sun, Jun 9, 2024 at 6:40 AM Jonathan Calmels <jcalmels@...0.net> wrote:
>
> This patch allows modifying the various capabilities of the struct cred
> in BPF-LSM hooks. More specifically, the userns_create hook called
> prior to creating a new user namespace.
>
> With the introduction of userns capabilities, this effectively provides
> a simple way for LSMs to control the capabilities granted to a user
> namespace and all its descendants.
>
> Update the selftests accordingly by dropping CAP_SYS_ADMIN in
> namespaces and checking the resulting task's bounding set.
>
> Signed-off-by: Jonathan Calmels <jcalmels@...0.net>
> ---
>  include/linux/lsm_hook_defs.h                 |  2 +-
>  include/linux/security.h                      |  4 +-
>  kernel/bpf/bpf_lsm.c                          | 55 +++++++++++++++++++
>  security/apparmor/lsm.c                       |  2 +-
>  security/security.c                           |  6 +-
>  security/selinux/hooks.c                      |  2 +-
>  .../selftests/bpf/prog_tests/deny_namespace.c | 12 ++--
>  .../selftests/bpf/progs/test_deny_namespace.c |  7 ++-
>  8 files changed, 76 insertions(+), 14 deletions(-)

I'm not sure we want to go down the path of a LSM modifying the POSIX
capabilities of a task, other than the capabilities/commoncap LSM.  It
sets a bad precedent and could further complicate issues around LSM
ordering.

--
paul-moore.com