On Thu, Aug 15, 2019 at 07:19:12PM +0200, Thomas Gleixner wrote:
> Dmitry,
>
> On Thu, 15 Aug 2019, Dmitry Safonov wrote:
> > 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/.
>
> > +++ 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.
>
> > + 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.
>
> > + }
> > + 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!
>
> > + */
> > +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.
>
> > + */
> > +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;
>
> > + 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.
>
> > +
> > + 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
