Re: [PATCH 1/3] selinux: Implement LSM notification system

[Casey Schaufler <casey@schaufler-ca.com>]

On 4/26/2017 10:36 AM, Stephen Smalley wrote:
> On Wed, 2017-04-26 at 08:38 -0700, Casey Schaufler wrote:
>> On 4/26/2017 8:02 AM, Sebastien Buisson wrote:
>>> From: Daniel Jurgens <danielj@mellanox.com>
>>>
>>> Add a generic notification mechanism in the LSM. Interested
>>> consumers
>>> can register a callback with the LSM and security modules can
>>> produce
>>> events.
>> Why is this a generic mechanism? Do you ever see anyone
>> other than SELinux using it?
> I do - any security module that wants to support access control over
> Lustre filesystems or Infiniband. Seems ironic for you to be arguing
> for a SELinux-specific interface rather than a LSM interface.

I lost the connection between this mechanism and
Lustre and Infiniband, neither of which are mentioned
in the patchset. And I *did* pose it as a question.
I am all in favor of general mechanisms where they
are generally useful. I am also adverse to special
purpose clutter.

>
>>> Add a call to the notification mechanism from SELinux when the AVC
>>> cache changes.
>> This seems like a whole lot of mechanism for
>> something you could accomplish with a log message.
>> What am I missing?
> It's a notification to a kernel subsystem that policy has changed so
> that the subsystem can update any cached state.
>
>>> Signed-off-by: Daniel Jurgens <danielj@mellanox.com>
>>> Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
>>> ---
>>>  include/linux/security.h | 23 +++++++++++++++++++++++
>>>  security/security.c      | 20 ++++++++++++++++++++
>>>  security/selinux/hooks.c | 12 ++++++++++++
>>>  3 files changed, 55 insertions(+)
>>>
>>> diff --git a/include/linux/security.h b/include/linux/security.h
>>> index af675b5..73a9c93 100644
>>> --- a/include/linux/security.h
>>> +++ b/include/linux/security.h
>>> @@ -68,6 +68,10 @@
>>>  struct user_namespace;
>>>  struct timezone;
>>>  
>>> +enum lsm_event {
>>> +	LSM_POLICY_CHANGE,
>>> +};
>>> +
>>>  /* These functions are in security/commoncap.c */
>>>  extern int cap_capable(const struct cred *cred, struct
>>> user_namespace *ns,
>>>  		       int cap, int audit);
>>> @@ -163,6 +167,10 @@ struct security_mnt_opts {
>>>  	int num_mnt_opts;
>>>  };
>>>  
>>> +int call_lsm_notifier(enum lsm_event event, void *data);
>>> +int register_lsm_notifier(struct notifier_block *nb);
>>> +int unregister_lsm_notifier(struct notifier_block *nb);
>>> +
>>>  static inline void security_init_mnt_opts(struct security_mnt_opts
>>> *opts)
>>>  {
>>>  	opts->mnt_opts = NULL;
>>> @@ -381,6 +389,21 @@ int security_sem_semop(struct sem_array *sma,
>>> struct sembuf *sops,
>>>  struct security_mnt_opts {
>>>  };
>>>  
>>> +static inline int call_lsm_notifier(enum lsm_event event, void
>>> *data)
>>> +{
>>> +	return 0;
>>> +}
>>> +
>>> +static inline int register_lsm_notifier(struct notifier_block *nb)
>>> +{
>>> +	return 0;
>>> +}
>>> +
>>> +static inline  int unregister_lsm_notifier(struct notifier_block
>>> *nb)
>>> +{
>>> +	return 0;
>>> +}
>>> +
>>>  static inline void security_init_mnt_opts(struct security_mnt_opts
>>> *opts)
>>>  {
>>>  }
>>> diff --git a/security/security.c b/security/security.c
>>> index b9fea39..ef9d9e1 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -32,6 +32,8 @@
>>>  /* Maximum number of letters for an LSM name string */
>>>  #define SECURITY_NAME_MAX	10
>>>  
>>> +static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
>>> +
>>>  struct security_hook_heads security_hook_heads
>>> __lsm_ro_after_init;
>>>  char *lsm_names;
>>>  /* Boot-time LSM user choice */
>>> @@ -146,6 +148,24 @@ void __init security_add_hooks(struct
>>> security_hook_list *hooks, int count,
>>>  		panic("%s - Cannot get early memory.\n",
>>> __func__);
>>>  }
>>>  
>>> +int call_lsm_notifier(enum lsm_event event, void *data)
>>> +{
>>> +	return atomic_notifier_call_chain(&lsm_notifier_chain,
>>> event, data);
>>> +}
>>> +EXPORT_SYMBOL(call_lsm_notifier);
>>> +
>>> +int register_lsm_notifier(struct notifier_block *nb)
>>> +{
>>> +	return atomic_notifier_chain_register(&lsm_notifier_chain,
>>> nb);
>>> +}
>>> +EXPORT_SYMBOL(register_lsm_notifier);
>>> +
>>> +int unregister_lsm_notifier(struct notifier_block *nb)
>>> +{
>>> +	return
>>> atomic_notifier_chain_unregister(&lsm_notifier_chain, nb);
>>> +}
>>> +EXPORT_SYMBOL(unregister_lsm_notifier);
>>> +
>>>  /*
>>>   * Hook list operation macros.
>>>   *
>>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>>> index e67a526..a4d36f8 100644
>>> --- a/security/selinux/hooks.c
>>> +++ b/security/selinux/hooks.c
>>> @@ -171,6 +171,14 @@ static int selinux_netcache_avc_callback(u32
>>> event)
>>>  	return 0;
>>>  }
>>>  
>>> +static int selinux_lsm_notifier_avc_callback(u32 event)
>>> +{
>>> +	if (event == AVC_CALLBACK_RESET)
>>> +		call_lsm_notifier(LSM_POLICY_CHANGE, NULL);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>>  /*
>>>   * initialise the security for the init task
>>>   */
>>> @@ -6379,6 +6387,10 @@ static __init int selinux_init(void)
>>>  	if (avc_add_callback(selinux_netcache_avc_callback,
>>> AVC_CALLBACK_RESET))
>>>  		panic("SELinux: Unable to register AVC netcache
>>> callback\n");
>>>  
>>> +	if (avc_add_callback(selinux_lsm_notifier_avc_callback,
>>> +			     AVC_CALLBACK_RESET))
>>> +		panic("SELinux: Unable to register AVC LSM
>>> notifier callback\n");
>>> +
>>>  	if (selinux_enforcing)
>>>  		printk(KERN_DEBUG "SELinux:  Starting in enforcing
>>> mode\n");
>>>  	else