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

Serge Hallyn
2013-12-09T17:53:43Z

Quoting Gao feng (gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org):
> On 12/07/2013 06:10 AM, Serge E. Hallyn wrote:
> > Quoting Gao feng (gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org):
> >> 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-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
> >> ---
> >> 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?
> >
>
> task doesn't hold namespace's refcount directly. it hold ns's refcount

No but when you create the new_nsp with create_new_namespaces(),
that new_nsp bumps the refcount on the init_audit_ns. Then you
point new_nsp to a new audit_ns, but you never drop the refcount
on init_audit_ns.

> through nsproxy. switch_task_namespaces will release the refcount of old
> nsproxy. so I think the refcount here is no problem.
>
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