Re: [PATCH v10 27/27] ima: Enable IMA namespaces

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/23/22 12:58, Serge E. Hallyn wrote:
> On Tue, Feb 01, 2022 at 03:37:35PM -0500, Stefan Berger wrote:
>> Introduce the IMA_NS in Kconfig for IMA namespace enablement.
>>
>> Enable the lazy initialization of an IMA namespace when a user mounts
>> SecurityFS and writes '1' into IMA's 'active' securityfs file. A
>> user_namespace will now get a pointer to an ima_namespace and therefore
>> implement get_current_ns() for the namespacing case that returns this
>> pointer. Use get_current_ns() in those places that require access to the
>> current IMA namespace. In some places, primarily those related to
>> IMA-appraisal and changes to file attributes, keep the pointer to
>> init_ima_ns, since there flags related to file measurements may be
>> affected, which are not supported in IMA namespaces, yet.
>>
>> Before using the ima_namespace pointer test it with ns_is_active()
>> to check whether it is NULL and whether the ima_namespace is active.
>> If it's not active, it cannot be used, yet. Therefore, return early
>> from those functions that may now get either get a NULL pointer from
>> this call or where ns->active is still 0. The init_ima_ns is always
>> set to be active, thus passing the check.
>>
>> Implement ima_ns_from_file() for SecurityFS-related files where we can
>> now get the IMA namespace via the user namespace pointer associated
>> with the superblock of the SecurityFS filesystem instance.
>>
>> Return -EACCES to IMA's securityfs files, except for the 'active' file,
>> until the IMA namespace has been set to active.
>>
>> Switch access to userns->ima_ns to use acquire/release semantics to ensure
>> that a newly created ima_namespace structure is fully visible upon access.
>>
>> Only emit the kernel log message 'policy update completed' for the
>> init_ima_ns.
>>
>> When parsing an IMA policy rule use the user namespace of the opener
>> to translate uid and gid values to kernel values rather than the user
>> namespace of the writer.
>>
>> Gate access to ima_appraise variable to init_ima_ns in ima_load_data()
>> and ima_write_policy().
>>
>> Gate access to temp_ima_appraise variable to init_ima_ns in
>> ima_delete_rules().
>>
>> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
>>
>> ---
>> v10:
>>   - dropped ima_ns_to_user_ns(); using current_user_ns() instead
>>   - Pass user_namespace of file opener into ima_parse_rule and propagate
>>     this parameter back all the way to the initial caller in the chain
>>   - Gate access to ima_appraise to init_ima_ns in ima_write_policy()
>>
>> v9:
>>   - ima_post_key_create_or_update: Only handle key if in init_ima_ns
>>   - Removed ns == NULL checks where user_namespace is now passed
>>   - Defer setting of user_ns->ima_ns until end of ima_fs_ns_init();
>>     required new ima_free_imans() and new user_ns_set_ima_ns()
>>   - Only emit log message 'policy update completed' for init_ima_ns
>>   - Introduce get_current_ns() only in this patch
>>   - Check for ns == &init_ima_ns in ima_load_data()
>> ---
>>   include/linux/ima.h                          |  1 +
>>   init/Kconfig                                 | 13 +++
>>   kernel/user_namespace.c                      |  2 +
>>   security/integrity/ima/ima.h                 | 55 +++++++++++--
>>   security/integrity/ima/ima_appraise.c        |  3 +
>>   security/integrity/ima/ima_asymmetric_keys.c |  6 +-
>>   security/integrity/ima/ima_fs.c              | 87 ++++++++++++++++----
>>   security/integrity/ima/ima_init.c            |  2 +-
>>   security/integrity/ima/ima_init_ima_ns.c     |  2 +
>>   security/integrity/ima/ima_main.c            | 34 +++++---
>>   security/integrity/ima/ima_ns.c              | 15 +++-
>>   security/integrity/ima/ima_policy.c          | 43 ++++++----
>>   12 files changed, 202 insertions(+), 61 deletions(-)
>>
>> diff --git a/include/linux/ima.h b/include/linux/ima.h
>> index c584527c0f47..a8cb2c269f61 100644
>> --- a/include/linux/ima.h
>> +++ b/include/linux/ima.h
>> @@ -11,6 +11,7 @@
>>   #include <linux/fs.h>
>>   #include <linux/security.h>
>>   #include <linux/kexec.h>
>> +#include <linux/user_namespace.h>
>>   #include <crypto/hash_info.h>
>>   struct linux_binprm;
>>   
>> diff --git a/init/Kconfig b/init/Kconfig
>> index 4b7bac10c72d..e27155e0ddba 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -1247,6 +1247,19 @@ config NET_NS
>>   	  Allow user space to create what appear to be multiple instances
>>   	  of the network stack.
>>   
>> +config IMA_NS
>> +	bool "IMA namespace"
>> +	depends on USER_NS
>> +	depends on IMA
>> +	default n
>> +	help
>> +	  Allow the creation of an IMA namespace for each user namespace.
>> +	  Namespaced IMA enables having IMA features work separately
>> +	  in each IMA namespace.
>> +	  Currently, only the audit status flags are stored in the namespace,
>> +	  which allows the same file to be audited each time it is accessed
>> +	  in a new namespace.
>> +
>>   endif # NAMESPACES
>>   
>>   config CHECKPOINT_RESTORE
>> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
>> index 6b2e3ca7ee99..653f8fa83b69 100644
>> --- a/kernel/user_namespace.c
>> +++ b/kernel/user_namespace.c
>> @@ -20,6 +20,7 @@
>>   #include <linux/fs_struct.h>
>>   #include <linux/bsearch.h>
>>   #include <linux/sort.h>
>> +#include <linux/ima.h>
>>   
>>   static struct kmem_cache *user_ns_cachep __read_mostly;
>>   static DEFINE_MUTEX(userns_state_mutex);
>> @@ -196,6 +197,7 @@ static void free_user_ns(struct work_struct *work)
>>   			kfree(ns->projid_map.forward);
>>   			kfree(ns->projid_map.reverse);
>>   		}
>> +		free_ima_ns(ns);
>>   		retire_userns_sysctls(ns);
>>   		key_free_user_ns(ns);
>>   		ns_free_inum(&ns->ns);
>> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
>> index 05e2de7697da..73df1d8a2ece 100644
>> --- a/security/integrity/ima/ima.h
>> +++ b/security/integrity/ima/ima.h
>> @@ -337,10 +337,10 @@ int ima_match_policy(struct ima_namespace *ns,
>>   		     int mask, int flags, int *pcr,
>>   		     struct ima_template_desc **template_desc,
>>   		     const char *func_data, unsigned int *allowed_algos);
>> -void ima_init_policy(struct ima_namespace *ns);
>> +void ima_init_policy(struct user_namespace *user_ns);
>>   void ima_update_policy(struct ima_namespace *ns);
>>   void ima_update_policy_flags(struct ima_namespace *ns);
>> -ssize_t ima_parse_add_rule(struct ima_namespace *ns, char *rule);
>> +ssize_t ima_parse_add_rule(struct user_namespace *user_ns, char *rule);
>>   void ima_delete_rules(struct ima_namespace *ns);
>>   int ima_check_policy(struct ima_namespace *ns);
>>   void ima_free_policy_rules(struct ima_namespace *ns);
>> @@ -538,32 +538,70 @@ struct user_namespace *ima_user_ns_from_file(const struct file *filp)
>>   	return file_inode(filp)->i_sb->s_user_ns;
>>   }
>>   
>> +#ifdef CONFIG_IMA_NS
>> +
>>   static inline struct ima_namespace
>>   *ima_ns_from_user_ns(struct user_namespace *user_ns)
>>   {
>> -	if (user_ns == &init_user_ns)
>> -		return &init_ima_ns;
>> -	return NULL;
>> +	/* Pairs with smp_store_releases() in user_ns_set_ima_ns(). */
>> +	return smp_load_acquire(&user_ns->ima_ns);
>>   }
>>   
>> -#ifdef CONFIG_IMA_NS
>> +static inline void user_ns_set_ima_ns(struct user_namespace *user_ns,
>> +				      struct ima_namespace *ns)
>> +{
>> +	/* Pairs with smp_load_acquire() in ima_ns_from_user_ns() */
>> +	smp_store_release(&user_ns->ima_ns, ns);
>> +}
>> +
>> +static inline struct ima_namespace *get_current_ns(void)
>> +{
>> +	return ima_ns_from_user_ns(current_user_ns());
>> +}
>>   
>>   struct ima_namespace *create_ima_ns(void);
>>   
>> +void ima_free_ima_ns(struct ima_namespace *ns);
>> +
>>   struct ns_status *ima_get_ns_status(struct ima_namespace *ns,
>>   				    struct inode *inode,
>>   				    struct integrity_iint_cache *iint);
>>   
>>   void ima_free_ns_status_tree(struct ima_namespace *ns);
>>   
>> +static inline struct ima_namespace *ima_ns_from_file(const struct file *filp)
>> +{
> Why is it ok here to dereference userns->ima_ns without
> going through ima_ns_from_user_ns() to do the smp_load_acquire()?

Good catch! Fixed.

     Stefan