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

[Daniel Jurgens]

On 4/26/2017 10:38 AM, Casey Schaufler wrote:
> On 4/26/2017 8:02 AM, Sebastien Buisson wrote:
>> From: Daniel Jurgens <danielj@xxxxxxxxxxxx>
>>
>> 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 had created an SELinux specific mechanism, Paul Moore requested I make it generic.
>> 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?
This was part of a larger patch set that hasn't been accepted yet.  SELinux support for Inifiniband.  Subsequent patches in that patch set will use it as well.
>> Signed-off-by: Daniel Jurgens <danielj@xxxxxxxxxxxx>
>> Signed-off-by: Sebastien Buisson <sbuisson@xxxxxxx>
>> ---
>>  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
>