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linux-next/kernel/time/namespace.c
Christian Brauner f2a8d52e0a
nsproxy: add struct nsset
Add a simple struct nsset. It holds all necessary pieces to switch to a new
set of namespaces without leaving a task in a half-switched state which we
will make use of in the next patch. This patch switches the existing setns
logic over without causing a change in setns() behavior. This brings
setns() closer to how unshare() works(). The prepare_ns() function is
responsible to prepare all necessary information. This has two reasons.
First it minimizes dependencies between individual namespaces, i.e. all
install handler can expect that all fields are properly initialized
independent in what order they are called in. Second, this makes the code
easier to maintain and easier to follow if it needs to be changed.

The prepare_ns() helper will only be switched over to use a flags argument
in the next patch. Here it will still use nstype as a simple integer
argument which was argued would be clearer. I'm not particularly
opinionated about this if it really helps or not. The struct nsset itself
already contains the flags field since its name already indicates that it
can contain information required by different namespaces. None of this
should have functional consequences.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Link: https://lore.kernel.org/r/20200505140432.181565-2-christian.brauner@ubuntu.com
2020-05-09 13:57:12 +02:00

485 lines
11 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Author: Andrei Vagin <avagin@openvz.org>
* Author: Dmitry Safonov <dima@arista.com>
*/
#include <linux/time_namespace.h>
#include <linux/user_namespace.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/clocksource.h>
#include <linux/seq_file.h>
#include <linux/proc_ns.h>
#include <linux/export.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/err.h>
#include <linux/mm.h>
#include <vdso/datapage.h>
ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
struct timens_offsets *ns_offsets)
{
ktime_t offset;
switch (clockid) {
case CLOCK_MONOTONIC:
offset = timespec64_to_ktime(ns_offsets->monotonic);
break;
case CLOCK_BOOTTIME:
case CLOCK_BOOTTIME_ALARM:
offset = timespec64_to_ktime(ns_offsets->boottime);
break;
default:
return tim;
}
/*
* Check that @tim value is in [offset, KTIME_MAX + offset]
* and subtract offset.
*/
if (tim < offset) {
/*
* User can specify @tim *absolute* value - if it's lesser than
* the time namespace's offset - it's already expired.
*/
tim = 0;
} else {
tim = ktime_sub(tim, offset);
if (unlikely(tim > KTIME_MAX))
tim = KTIME_MAX;
}
return tim;
}
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);
}
/**
* clone_time_ns - Clone a time namespace
* @user_ns: User namespace which owns a new namespace.
* @old_ns: Namespace to clone
*
* Clone @old_ns and set the clone refcount to 1
*
* Return: The new namespace or ERR_PTR.
*/
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 = kmalloc(sizeof(*ns), GFP_KERNEL);
if (!ns)
goto fail_dec;
kref_init(&ns->kref);
ns->vvar_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!ns->vvar_page)
goto fail_free;
err = ns_alloc_inum(&ns->ns);
if (err)
goto fail_free_page;
ns->ucounts = ucounts;
ns->ns.ops = &timens_operations;
ns->user_ns = get_user_ns(user_ns);
ns->offsets = old_ns->offsets;
ns->frozen_offsets = false;
return ns;
fail_free_page:
__free_page(ns->vvar_page);
fail_free:
kfree(ns);
fail_dec:
dec_time_namespaces(ucounts);
fail:
return ERR_PTR(err);
}
/**
* copy_time_ns - Create timens_for_children from @old_ns
* @flags: Cloning flags
* @user_ns: User namespace which owns a new namespace.
* @old_ns: Namespace to clone
*
* If CLONE_NEWTIME specified in @flags, creates a new timens_for_children;
* adds a refcounter to @old_ns otherwise.
*
* Return: timens_for_children namespace or ERR_PTR.
*/
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);
}
static struct timens_offset offset_from_ts(struct timespec64 off)
{
struct timens_offset ret;
ret.sec = off.tv_sec;
ret.nsec = off.tv_nsec;
return ret;
}
/*
* A time namespace VVAR page has the same layout as the VVAR page which
* contains the system wide VDSO data.
*
* For a normal task the VVAR pages are installed in the normal ordering:
* VVAR
* PVCLOCK
* HVCLOCK
* TIMENS <- Not really required
*
* Now for a timens task the pages are installed in the following order:
* TIMENS
* PVCLOCK
* HVCLOCK
* VVAR
*
* The check for vdso_data->clock_mode is in the unlikely path of
* the seq begin magic. So for the non-timens case most of the time
* 'seq' is even, so the branch is not taken.
*
* If 'seq' is odd, i.e. a concurrent update is in progress, the extra check
* for vdso_data->clock_mode is a non-issue. The task is spin waiting for the
* update to finish and for 'seq' to become even anyway.
*
* Timens page has vdso_data->clock_mode set to VDSO_CLOCKMODE_TIMENS which
* enforces the time namespace handling path.
*/
static void timens_setup_vdso_data(struct vdso_data *vdata,
struct time_namespace *ns)
{
struct timens_offset *offset = vdata->offset;
struct timens_offset monotonic = offset_from_ts(ns->offsets.monotonic);
struct timens_offset boottime = offset_from_ts(ns->offsets.boottime);
vdata->seq = 1;
vdata->clock_mode = VDSO_CLOCKMODE_TIMENS;
offset[CLOCK_MONOTONIC] = monotonic;
offset[CLOCK_MONOTONIC_RAW] = monotonic;
offset[CLOCK_MONOTONIC_COARSE] = monotonic;
offset[CLOCK_BOOTTIME] = boottime;
offset[CLOCK_BOOTTIME_ALARM] = boottime;
}
/*
* Protects possibly multiple offsets writers racing each other
* and tasks entering the namespace.
*/
static DEFINE_MUTEX(offset_lock);
static void timens_set_vvar_page(struct task_struct *task,
struct time_namespace *ns)
{
struct vdso_data *vdata;
unsigned int i;
if (ns == &init_time_ns)
return;
/* Fast-path, taken by every task in namespace except the first. */
if (likely(ns->frozen_offsets))
return;
mutex_lock(&offset_lock);
/* Nothing to-do: vvar_page has been already initialized. */
if (ns->frozen_offsets)
goto out;
ns->frozen_offsets = true;
vdata = arch_get_vdso_data(page_address(ns->vvar_page));
for (i = 0; i < CS_BASES; i++)
timens_setup_vdso_data(&vdata[i], ns);
out:
mutex_unlock(&offset_lock);
}
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);
__free_page(ns->vvar_page);
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 nsset *nsset, struct ns_common *new)
{
struct nsproxy *nsproxy = nsset->nsproxy;
struct time_namespace *ns = to_time_ns(new);
int err;
if (!current_is_single_threaded())
return -EUSERS;
if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
!ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
return -EPERM;
timens_set_vvar_page(current, ns);
err = vdso_join_timens(current, ns);
if (err)
return err;
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;
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);
int err;
/* create_new_namespaces() already incremented the ref counter */
if (nsproxy->time_ns == nsproxy->time_ns_for_children)
return 0;
timens_set_vvar_page(tsk, ns);
err = vdso_join_timens(tsk, ns);
if (err)
return err;
get_time_ns(ns);
put_time_ns(nsproxy->time_ns);
nsproxy->time_ns = ns;
return 0;
}
static struct user_namespace *timens_owner(struct ns_common *ns)
{
return to_time_ns(ns)->user_ns;
}
static void show_offset(struct seq_file *m, int clockid, struct timespec64 *ts)
{
char *clock;
switch (clockid) {
case CLOCK_BOOTTIME:
clock = "boottime";
break;
case CLOCK_MONOTONIC:
clock = "monotonic";
break;
default:
clock = "unknown";
break;
}
seq_printf(m, "%-10s %10lld %9ld\n", clock, ts->tv_sec, ts->tv_nsec);
}
void proc_timens_show_offsets(struct task_struct *p, struct seq_file *m)
{
struct ns_common *ns;
struct time_namespace *time_ns;
ns = timens_for_children_get(p);
if (!ns)
return;
time_ns = to_time_ns(ns);
show_offset(m, CLOCK_MONOTONIC, &time_ns->offsets.monotonic);
show_offset(m, CLOCK_BOOTTIME, &time_ns->offsets.boottime);
put_time_ns(time_ns);
}
int proc_timens_set_offset(struct file *file, struct task_struct *p,
struct proc_timens_offset *offsets, int noffsets)
{
struct ns_common *ns;
struct time_namespace *time_ns;
struct timespec64 tp;
int i, err;
ns = timens_for_children_get(p);
if (!ns)
return -ESRCH;
time_ns = to_time_ns(ns);
if (!file_ns_capable(file, time_ns->user_ns, CAP_SYS_TIME)) {
put_time_ns(time_ns);
return -EPERM;
}
for (i = 0; i < noffsets; i++) {
struct proc_timens_offset *off = &offsets[i];
switch (off->clockid) {
case CLOCK_MONOTONIC:
ktime_get_ts64(&tp);
break;
case CLOCK_BOOTTIME:
ktime_get_boottime_ts64(&tp);
break;
default:
err = -EINVAL;
goto out;
}
err = -ERANGE;
if (off->val.tv_sec > KTIME_SEC_MAX ||
off->val.tv_sec < -KTIME_SEC_MAX)
goto out;
tp = timespec64_add(tp, off->val);
/*
* KTIME_SEC_MAX is divided by 2 to be sure that KTIME_MAX is
* still unreachable.
*/
if (tp.tv_sec < 0 || tp.tv_sec > KTIME_SEC_MAX / 2)
goto out;
}
mutex_lock(&offset_lock);
if (time_ns->frozen_offsets) {
err = -EACCES;
goto out_unlock;
}
err = 0;
/* Don't report errors after this line */
for (i = 0; i < noffsets; i++) {
struct proc_timens_offset *off = &offsets[i];
struct timespec64 *offset = NULL;
switch (off->clockid) {
case CLOCK_MONOTONIC:
offset = &time_ns->offsets.monotonic;
break;
case CLOCK_BOOTTIME:
offset = &time_ns->offsets.boottime;
break;
}
*offset = off->val;
}
out_unlock:
mutex_unlock(&offset_lock);
out:
put_time_ns(time_ns);
return err;
}
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",
.real_ns_name = "time",
.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,
.frozen_offsets = true,
};
static int __init time_ns_init(void)
{
return 0;
}
subsys_initcall(time_ns_init);