Re: [PATCH v10 15/27] ima: Implement hierarchical processing of file accesses

[Mimi Zohar <zohar@linux.ibm.com>]

On Tue, 2022-02-01 at 15:37 -0500, Stefan Berger wrote:
> Implement hierarchical processing of file accesses in IMA namespaces by
> walking the list of user namespaces towards the root. This way file
> accesses can be audited in an IMA namespace and also be evaluated against
> the IMA policies of parent IMA namespaces.
> 
> Pass the user_namespace into process_measurement since we will be walking
> the hierarchy of user_namespaces towards the init_user_ns and we can easily
> derive the ima_namespace from the user_namespace.
> 
> __process_measurement() returns either 0 or -EACCES. For hierarchical
> processing remember the -EACCES returned by this function but continue
> to the parent user namespace. At the end either return 0 or -EACCES
> if an error occurred in one of the IMA namespaces.
> 
> Currently the ima_ns pointer of the user_namespace is always NULL except
> at the init_user_ns, so test ima_ns for NULL pointer and skip the call to
> __process_measurement() if it is NULL. Once IMA namespacing is fully
> enabled, the pointer may still be NULL due to late initialization of the
> IMA namespace.
> 
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> 
> ---
> 
> v10:
>   - Fixed compilation issue
> 
> v9:
>   - Switch callers to pass user_namespace rather than ima_namespace with
>     potential NULL pointer
>   - Add default case to switch statement and warn if this happens
>   - Implement ima_ns_from_user_ns() in this patch now
> ---
>  security/integrity/ima/ima.h      |  8 ++++
>  security/integrity/ima/ima_main.c | 76 +++++++++++++++++++++++--------
>  2 files changed, 65 insertions(+), 19 deletions(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 0057b1fd6c18..aea8fb8d2854 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -493,4 +493,12 @@ struct user_namespace *ima_user_ns_from_file(const struct file *filp)
>  	return file_inode(filp)->i_sb->s_user_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;
> +}
> +
>  #endif /* __LINUX_IMA_H */
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index ae0e9b14554a..917504319e7f 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -196,10 +196,10 @@ void ima_file_free(struct file *file)
>  	ima_check_last_writer(iint, inode, file);
>  }
>  
> -static int process_measurement(struct ima_namespace *ns,
> -			       struct file *file, const struct cred *cred,
> -			       u32 secid, char *buf, loff_t size, int mask,
> -			       enum ima_hooks func)
> +static int __process_measurement(struct ima_namespace *ns,
> +				 struct file *file, const struct cred *cred,
> +				 u32 secid, char *buf, loff_t size, int mask,
> +				 enum ima_hooks func)
>  {
>  	struct inode *inode = file_inode(file);
>  	struct integrity_iint_cache *iint = NULL;
> @@ -391,6 +391,41 @@ static int process_measurement(struct ima_namespace *ns,
>  	return 0;
>  }
>  
> +static int process_measurement(struct user_namespace *user_ns,
> +			       struct file *file, const struct cred *cred,
> +			       u32 secid, char *buf, loff_t size, int mask,
> +			       enum ima_hooks func)
> +{
> +	struct ima_namespace *ns;
> +	int ret = 0;
> +
> +	while (user_ns) {
> +		ns = ima_ns_from_user_ns(user_ns);
> +		if (ns) {
> +			int rc;
> +
> +			rc = __process_measurement(ns, file, cred, secid, buf,
> +						   size, mask, func);
> +			switch (rc) {
> +			case 0:
> +				break;
> +			case -EACCES:
> +				/* return this error at the end but continue */
> +				ret = -EACCES;
> +				break;
> +			default:
> +				/* should not happen */
> +				ret = -EACCES;
> +				WARN_ON_ONCE(true);
> +			}
> +		}
> +
> +		user_ns = user_ns->parent;
> +	};
> +
> +	return ret;
> +}
> +

Very nice and concise!

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>

-- 
thanks,

Mimi