[RFC PATCH 29/29] lsm: add support for counting lsm_prop support among LSMs

[Casey Schaufler]

On 5/13/2025 1:23 PM, Paul Moore wrote:
> On Tue, May 13, 2025 at 12:39 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
>> On 4/9/2025 11:50 AM, Paul Moore wrote:
>>> Add two new variables, lsm_count_prop_subj and lsm_count_prop_obj, to
>>> count the number of lsm_prop entries for subjects and objects across all
>>> of the enabled LSMs.  Future patches will use this to continue the
>>> conversion towards the lsm_prop struct.
>>>
>>> Signed-off-by: Paul Moore <paul at paul-moore.com>
>>> ---
>>>  include/linux/lsm_hooks.h         | 6 ++++++
>>>  security/apparmor/lsm.c           | 1 +
>>>  security/bpf/hooks.c              | 1 +
>>>  security/commoncap.c              | 1 +
>>>  security/integrity/evm/evm_main.c | 1 +
>>>  security/integrity/ima/ima_main.c | 1 +
>>>  security/ipe/ipe.c                | 1 +
>>>  security/landlock/setup.c         | 1 +
>>>  security/loadpin/loadpin.c        | 1 +
>>>  security/lockdown/lockdown.c      | 1 +
>>>  security/lsm.h                    | 4 ++++
>>>  security/lsm_init.c               | 6 ++++++
>>>  security/safesetid/lsm.c          | 1 +
>>>  security/security.c               | 3 +++
>>>  security/selinux/hooks.c          | 1 +
>>>  security/smack/smack_lsm.c        | 1 +
>>>  security/tomoyo/tomoyo.c          | 1 +
>>>  security/yama/yama_lsm.c          | 1 +
>>>  18 files changed, 33 insertions(+)
> ..
>
>>> diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
>>> index 40efde233f3a..c72df6ff69f7 100644
>>> --- a/security/bpf/hooks.c
>>> +++ b/security/bpf/hooks.c
>>> @@ -18,6 +18,7 @@ static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
>>>  static const struct lsm_id bpf_lsmid = {
>>>       .name = "bpf",
>>>       .id = LSM_ID_BPF,
>>> +     .flags = LSM_ID_FLG_PROP_SUBJ | LSM_ID_FLG_PROP_OBJ,
>> There's a problem here. BPF can have properties, but usually does not.
>> Unless there's a bpf program loaded that provides them it is incorrect
>> to use these flags. You can't know that at initialization.
>>
>> I have an alternative that will address this that I will propose
>> shortly.
> Okay, thanks.

In my coming audit patch I changed where the counts of properties are
maintained from the LSM infrastructure to the audit subsystem, where they are
actually used. Instead of the LSM init code counting the property users, the
individual LSM init functions call an audit function that keeps track. BPF
could call that audit function if it loads a program that uses contexts. That
could happen after init, and the audit system would handle it properly.
Unloading the bpf program would be problematic. I honestly don't know whether
that's permitted.