Re: [PATCH 18/20] audit: add new message type AUDIT_CREATE_NS

[Serge E. Hallyn]

Quoting Gao feng (gaofeng@xxxxxxxxxxxxxx):
> Since there is no more place for flags of clone system call.
> we need to find a way to create audit namespace.
> 
> this patch add a new type of message AUDIT_CREATE_NS.
> user space can create new audit namespace through
> netlink.
> 
> Right now, The privileged user in user namespace is allowed
> to create audit namespace. it means the unprivileged user can
> create an user namespace and then create audit namespace.
> 
> Looks like it is not safe, but even the unprivileged user can
> create audit namespace, it can do no harm to the host. un-init
> audit namespace cann't effect the host.
> 
> In the follow patches, the audit_backlog_limit will be per
> audit namesapace, but only the privileged user has rights to
> modify it. and the default value of audit_backlog_limit for
> uninit audit namespace will be set to 0.
> 
> And the audit_rate_limit will be limited too.
> 
> Signed-off-by: Gao feng <gaofeng@xxxxxxxxxxxxxx>
> ---
>  include/linux/audit_namespace.h |  7 +++++++
>  include/uapi/linux/audit.h      |  1 +
>  kernel/audit.c                  | 22 ++++++++++++++++++++++
>  kernel/audit_namespace.c        | 29 +++++++++++++++++++++++++++++
>  4 files changed, 59 insertions(+)
> 
> diff --git a/include/linux/audit_namespace.h b/include/linux/audit_namespace.h
> index 79a9b78..b17f052 100644
> --- a/include/linux/audit_namespace.h
> +++ b/include/linux/audit_namespace.h
> @@ -54,6 +54,8 @@ void put_audit_ns(struct audit_namespace *ns)
>  		rcu_read_unlock();
>  	}
>  }
> +
> +extern int unshare_audit_namespace(void);
>  #else
>  static inline
>  struct audit_namespace *get_audit_ns(struct audit_namespace *ns)
> @@ -66,6 +68,11 @@ void put_audit_ns(struct audit_namespace *ns)
>  {
>  
>  }
> +
> +static inline int unshare_audit_namespace()
> +{
> +	return -EINVAL;
> +}
>  #endif
>  
>  static inline struct
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 75cef3f..877d509 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -68,6 +68,7 @@
>  #define AUDIT_MAKE_EQUIV	1015	/* Append to watched tree */
>  #define AUDIT_TTY_GET		1016	/* Get TTY auditing status */
>  #define AUDIT_TTY_SET		1017	/* Set TTY auditing status */
> +#define AUDIT_CREATE_NS		1018	/* Create new audit namespace */
>  
>  #define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */
>  #define AUDIT_USER_AVC		1107	/* We filter this differently */
> diff --git a/kernel/audit.c b/kernel/audit.c
> index c4d4291..86212d3 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -596,6 +596,12 @@ static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
>  		    !capable(CAP_AUDIT_CONTROL))
>  			err = -EPERM;
>  		break;
> +	case AUDIT_CREATE_NS:
> +		/* Allow privileged user in user namespace to
> +		 * create audit namespace */
> +		if (!ns_capable(current_user_ns(), CAP_AUDIT_CONTROL))
> +			err = -EPERM;
> +		break;
>  	case AUDIT_USER:
>  	case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
>  	case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
> @@ -735,6 +741,22 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
>  		if (status_get->mask & AUDIT_STATUS_BACKLOG_LIMIT)
>  			err = audit_set_backlog_limit(status_get->backlog_limit);
>  		break;
> +	case AUDIT_CREATE_NS:
> +		err = unshare_audit_namespace();
> +
> +		if (audit_enabled == AUDIT_OFF)
> +			break;
> +
> +		ab = audit_log_start_ns(ns, NULL, GFP_KERNEL, AUDIT_CREATE_NS);
> +		if (ab) {
> +			audit_log_format(ab, "Create audit namespace");
> +			audit_log_session_info(ab);
> +			audit_log_task_context(ab);
> +			audit_log_format(ab, "res=%d", err ? 0 : 1);
> +			audit_log_end_ns(ns, ab);
> +		}
> +
> +		break;
>  	case AUDIT_USER:
>  	case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
>  	case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
> diff --git a/kernel/audit_namespace.c b/kernel/audit_namespace.c
> index 6d9cb8f..28c608e 100644
> --- a/kernel/audit_namespace.c
> +++ b/kernel/audit_namespace.c
> @@ -6,3 +6,32 @@ struct audit_namespace init_audit_ns = {
>  	.user_ns = &init_user_ns,
>  };
>  EXPORT_SYMBOL_GPL(init_audit_ns);
> +
> +int unshare_audit_namespace(void)
> +{
> +	struct task_struct *tsk = current;
> +	struct audit_namespace *new_audit = NULL;
> +	struct nsproxy *new_nsp;
> +
> +	new_audit = kzalloc(sizeof(struct audit_namespace), GFP_KERNEL);
> +	if (!new_audit)
> +		return -ENOMEM;
> +
> +	skb_queue_head_init(&new_audit->queue);
> +	skb_queue_head_init(&new_audit->hold_queue);
> +	init_waitqueue_head(&new_audit->kauditd_wait);
> +	init_waitqueue_head(&new_audit->backlog_wait);
> +
> +	new_nsp = create_new_namespaces(0, tsk, NULL, NULL);
> +	if (IS_ERR(new_nsp)) {
> +		kfree(new_audit);
> +		return PTR_ERR(new_nsp);
> +	}
> +
> +	new_audit->user_ns = get_user_ns(current_user_ns());
> +	new_nsp->audit_ns = get_audit_ns(new_audit);
> +
> +	switch_task_namespaces(current, new_nsp);

Do you need to drop the old audit->ns refcount?

> +
> +	return 0;
> +}
> -- 
> 1.8.3.1
> 
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