Re: [PATCHv6 01/36] ns: Introduce Time Namespace

On Thu, Aug 15, 2019 at 07:19:12PM +0200, Thomas Gleixner wrote:

Dmitry,

On Thu, 15 Aug 2019, Dmitry Safonov wrote:

quoted

diff --git a/MAINTAINERS b/MAINTAINERS
index 420567d1519a..97b7737f5aba 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -12898,6 +12898,8 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core
 S:	Maintained
 F:	fs/timerfd.c
 F:	include/linux/timer*
+F:	include/linux/time_namespace.h
+F:	kernel/time_namespace.c

Shouldn't this be kernel/time/namespace.c so all that stuff is lumped
together. No strong opinion though.

Sure, we can move this in kernel/time. I don't remember why I decided to
place it in kernel/.

quoted

+++ b/kernel/time_namespace.c
+static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, current_euid(), UCOUNT_TIME_NAMESPACES);
+}
+
+static void dec_time_namespaces(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_TIME_NAMESPACES);
+}
+
+static struct time_namespace *create_time_ns(void)
+{
+	struct time_namespace *time_ns;
+
+	time_ns = kmalloc(sizeof(struct time_namespace), GFP_KERNEL);

Shouldn't this use kzalloc()? There are tons of members in that struct.

I don't think so. All of other members are initialized in clone_time_ns.
Maybe we don't need this helper. When I wrote this code, I looked at
kernel/utsname.c. I will think what we can do here to make this code
more clear.

quoted

+	if (time_ns) {
+		kref_init(&time_ns->kref);
+		time_ns->initialized = false;

And you spare this one.

This one should be initialized in clone_time_ns too.

quoted

+	}
+	return time_ns;
+}
+
+/*
+ * Clone a new ns copying @old_ns, setting refcount to 1
+ * @old_ns: namespace to clone
+ * Return the new ns or ERR_PTR.

If you use kernel-doc style then please use te proper syntax

/*
 * clone_time_ns - Clone a time namespace
 * @old_ns:	Namespace to clone
 *
 * Clone @old_ns and set the clone refcount to 1
 *
 * Return: The new namespace or ERR_PTR.
 */

Will fix. Thanks!

quoted

+ */
+static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
+					  struct time_namespace *old_ns)
+{
+	struct time_namespace *ns;
+	struct ucounts *ucounts;
+	int err;
+
+	err = -ENOSPC;
+	ucounts = inc_time_namespaces(user_ns);
+	if (!ucounts)
+		goto fail;
+
+	err = -ENOMEM;
+	ns = create_time_ns();
+	if (!ns)
+		goto fail_dec;
+
+	err = ns_alloc_inum(&ns->ns);
+	if (err)
+		goto fail_free;
+
+	ns->ucounts = ucounts;
+	ns->ns.ops = &timens_operations;
+	ns->user_ns = get_user_ns(user_ns);
+	return ns;
+
+fail_free:
+	kfree(ns);
+fail_dec:
+	dec_time_namespaces(ucounts);
+fail:
+	return ERR_PTR(err);
+}
+
+/*
+ * Add a reference to old_ns, or clone it if @flags specify CLONE_NEWTIME.
+ * In latter case, changes to the time of this process won't be seen by parent,
+ * and vice versa.

Ditto

Will fix.

quoted

+ */
+struct time_namespace *copy_time_ns(unsigned long flags,
+	struct user_namespace *user_ns, struct time_namespace *old_ns)
+{
+	if (!(flags & CLONE_NEWTIME))
+		return get_time_ns(old_ns);
+
+	return clone_time_ns(user_ns, old_ns);
+}
+
+void free_time_ns(struct kref *kref)
+{
+	struct time_namespace *ns;
+
+	ns = container_of(kref, struct time_namespace, kref);
+	dec_time_namespaces(ns->ucounts);
+	put_user_ns(ns->user_ns);
+	ns_free_inum(&ns->ns);
+	kfree(ns);
+}
+
+static struct time_namespace *to_time_ns(struct ns_common *ns)
+{
+	return container_of(ns, struct time_namespace, ns);
+}
+
+static struct ns_common *timens_get(struct task_struct *task)
+{
+	struct time_namespace *ns = NULL;
+	struct nsproxy *nsproxy;
+
+	task_lock(task);
+	nsproxy = task->nsproxy;
+	if (nsproxy) {
+		ns = nsproxy->time_ns;
+		get_time_ns(ns);
+	}
+	task_unlock(task);
+
+	return ns ? &ns->ns : NULL;
+}
+
+static struct ns_common *timens_for_children_get(struct task_struct *task)
+{
+	struct time_namespace *ns = NULL;
+	struct nsproxy *nsproxy;
+
+	task_lock(task);
+	nsproxy = task->nsproxy;
+	if (nsproxy) {
+		ns = nsproxy->time_ns_for_children;
+		get_time_ns(ns);
+	}
+	task_unlock(task);
+
+	return ns ? &ns->ns : NULL;
+}
+
+static void timens_put(struct ns_common *ns)
+{
+	put_time_ns(to_time_ns(ns));
+}
+
+static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
+{
+	struct time_namespace *ns = to_time_ns(new);
+
+	if (!current_is_single_threaded())
+		return -EUSERS;
+
+	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
+	    !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+		return -EPERM;
+
+	get_time_ns(ns);
+	get_time_ns(ns);

Why is this a double get?

Because we change nsproxy->time_ns and nsproxy->time_ns_for_children.

Probably, I need to reorgonize the code this way:

	get_time_ns(ns);
	put_time_ns(nsproxy->time_ns);
	nsproxy->time_ns = ns;

	get_time_ns(ns);
	put_time_ns(nsproxy->time_ns_for_children);
	nsproxy->time_ns_for_children = ns;

quoted

+	put_time_ns(nsproxy->time_ns);
+	put_time_ns(nsproxy->time_ns_for_children);
+	nsproxy->time_ns = ns;
+	nsproxy->time_ns_for_children = ns;
+	ns->initialized = true;
+	return 0;
+}
+
+int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk)
+{
+	struct ns_common *nsc = &nsproxy->time_ns_for_children->ns;
+	struct time_namespace *ns = to_time_ns(nsc);
+
+	if (nsproxy->time_ns == nsproxy->time_ns_for_children)
+		return 0;
+
+	get_time_ns(ns);
+	put_time_ns(nsproxy->time_ns);
+	nsproxy->time_ns = ns;
+	ns->initialized = true;

Isn't that one initialized already?

When we discussed time namespaces last year, we decided that clock
offsets can be set only before any task enters a namespace.

When a namespace is created, ns->initialized is set to false. When a
task enters the namespace, ns->initialized is set to true.

Namespace clock offsets can be changed only if ns->initialized is false.

A new task can be forked to a specified time namespace or it can call
setns, so we set ns->initialized to true in timens_on_fork and
timens_install.

quoted

+
+	return 0;
+}
+
+static struct user_namespace *timens_owner(struct ns_common *ns)
+{
+	return to_time_ns(ns)->user_ns;
+}
+
+const struct proc_ns_operations timens_operations = {
+	.name		= "time",
+	.type		= CLONE_NEWTIME,
+	.get		= timens_get,
+	.put		= timens_put,
+	.install	= timens_install,
+	.owner		= timens_owner,
+};
+
+const struct proc_ns_operations timens_for_children_operations = {
+	.name		= "time_for_children",
+	.type		= CLONE_NEWTIME,
+	.get		= timens_for_children_get,
+	.put		= timens_put,
+	.install	= timens_install,
+	.owner		= timens_owner,
+};
+
+struct time_namespace init_time_ns = {
+	.kref = KREF_INIT(3),
+	.user_ns = &init_user_ns,
+	.ns.inum = PROC_TIME_INIT_INO,
+	.ns.ops = &timens_operations,
+};

Inconsisten formatting. The above static initializers are nicely
tabular. This on not.

Will fix. Thanks.

Thanks,
Andrei

Thanks,

	tglx