While creating a LSM BPF MAC policy to block user namespace creation, we
used the LSM cred_prepare hook because that is the closest hook to prevent
a call to create_user_ns().
The calls look something like this:
cred = prepare_creds()
security_prepare_creds()
call_int_hook(cred_prepare, ...
if (cred)
create_user_ns(cred)
We noticed that error codes were not propagated from this hook and
introduced a patch [1] to propagate those errors.
The discussion notes that security_prepare_creds()
is not appropriate for MAC policies, and instead the hook is
meant for LSM authors to prepare credentials for mutation. [2]
Ultimately, we concluded that a better course of action is to introduce
a new security hook for LSM authors. [3]
This patch set first introduces a new security_create_user_ns() function
and create_user_ns LSM hook, then marks the hook as sleepable in BPF.
Links:
1. https://lore.kernel.org/all/20220608150942.776446-1-fred@xxxxxxxxxxxxxx/
2. https://lore.kernel.org/all/87y1xzyhub.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
3. https://lore.kernel.org/all/9fe9cd9f-1ded-a179-8ded-5fde8960a586@xxxxxxxxxxxxxx/
Frederick Lawler (2):
security, lsm: Introduce security_create_user_ns()
bpf-lsm: Make bpf_lsm_create_user_ns() sleepable
include/linux/lsm_hook_defs.h | 2 ++
include/linux/lsm_hooks.h | 5 +++++
include/linux/security.h | 8 ++++++++
kernel/bpf/bpf_lsm.c | 1 +
kernel/user_namespace.c | 5 +++++
security/security.c | 6 ++++++
6 files changed, 27 insertions(+)
--
2.30.2
