On Sun, Jun 09, 2024 at 08:18:48PM GMT, Paul Moore wrote:
On Sun, Jun 9, 2024 at 6:40 AM Jonathan Calmels jcalmels@3xx0.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@3xx0.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.
Well unless I'm misunderstanding, this does allow modifying the capabilities/commoncap LSM through BTF. The reason for allowing `userns_create` to be modified is that it is functionally very similar to `cred_prepare` in that it operates with new creds (but specific to user namespaces because of reasons detailed in [1]).
There were some concerns in previous threads that the userns caps by themselves wouldn't be granular enough, hence the LSM integration. Ubuntu for example, currently has to resort to a hardcoded profile transition to achieve this [2].
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... [2] https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble/com...