[PATCH 2/3] lsm: introduce security_lsm_manage_policy hook

[John Johansen]

On 5/7/25 08:37, Maxime Bélair wrote:
> 
> 
> On 5/7/25 08:19, Song Liu wrote:
>> On Tue, May 6, 2025 at 7:40 AM Maxime Bélair
>> <maxime.belair at canonical.com> wrote:
>>>
>>> Define a new LSM hook security_lsm_manage_policy and wire it into the
>>> lsm_manage_policy() syscall so that LSMs can register a unified interface
>>> for policy management. This initial, minimal implementation only supports
>>> the LSM_POLICY_LOAD operation to limit changes.
>>>
>>> Signed-off-by: Maxime Bélair <maxime.belair at canonical.com>
>> [...]
>>> diff --git a/security/security.c b/security/security.c
>>> index fb57e8fddd91..256104e338b1 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -5883,6 +5883,27 @@ int security_bdev_setintegrity(struct block_device *bdev,
>>>   }
>>>   EXPORT_SYMBOL(security_bdev_setintegrity);
>>>
>>> +/**
>>> + * security_lsm_manage_policy() - Manage the policies of LSMs
>>> + * @lsm_id: id of the lsm to target
>>> + * @op: Operation to perform (one of the LSM_POLICY_XXX values)
>>> + * @buf:  userspace pointer to policy data
>>> + * @size: size of @buf
>>> + * @flags: lsm policy management flags
>>> + *
>>> + * Manage the policies of a LSM. This notably allows to update them even when
>>> + * the lsmfs is unavailable is restricted. Currently, only LSM_POLICY_LOAD is
>>> + * supported.
>>> + *
>>> + * Return: Returns 0 on success, error on failure.
>>> + */
>>> +int security_lsm_manage_policy(u32 lsm_id, u32 op, void __user *buf,
>>> +                              size_t size, u32 flags)
>>> +{
>>> +       return call_int_hook(lsm_manage_policy, lsm_id, op, buf, size, flags);
>>
>> If the LSM doesn't implement this hook, sys_lsm_manage_policy will return 0
>> for any inputs, right? This is gonna be so confusing for users.
> 
> Indeed, that was an oversight. It will return -EOPNOTSUPP in the next patch revision.
> 

I think it needs to do more than that. I don't think this should call each LSM, the
infrastructure should filter it and only send it to the LSM identified by the lsm_id