1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Author: Andrei Vagin <avagin@openvz.org>
4 * Author: Dmitry Safonov <dima@arista.com>
5 */
6
7#include <linux/time_namespace.h>
8#include <linux/user_namespace.h>
9#include <linux/sched/signal.h>
10#include <linux/sched/task.h>
11#include <linux/clocksource.h>
12#include <linux/seq_file.h>
13#include <linux/proc_ns.h>
14#include <linux/export.h>
15#include <linux/nstree.h>
16#include <linux/time.h>
17#include <linux/slab.h>
18#include <linux/cred.h>
19#include <linux/err.h>
20#include <linux/mm.h>
21
22#include <vdso/datapage.h>
23
24ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
25 struct timens_offsets *ns_offsets)
26{
27 ktime_t offset;
28
29 switch (clockid) {
30 case CLOCK_MONOTONIC:
31 offset = timespec64_to_ktime(ts: ns_offsets->monotonic);
32 break;
33 case CLOCK_BOOTTIME:
34 case CLOCK_BOOTTIME_ALARM:
35 offset = timespec64_to_ktime(ts: ns_offsets->boottime);
36 break;
37 default:
38 return tim;
39 }
40
41 /*
42 * Check that @tim value is in [offset, KTIME_MAX + offset]
43 * and subtract offset.
44 */
45 if (tim < offset) {
46 /*
47 * User can specify @tim *absolute* value - if it's lesser than
48 * the time namespace's offset - it's already expired.
49 */
50 tim = 0;
51 } else {
52 tim = ktime_sub(tim, offset);
53 if (unlikely(tim > KTIME_MAX))
54 tim = KTIME_MAX;
55 }
56
57 return tim;
58}
59
60static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
61{
62 return inc_ucount(ns, current_euid(), type: UCOUNT_TIME_NAMESPACES);
63}
64
65static void dec_time_namespaces(struct ucounts *ucounts)
66{
67 dec_ucount(ucounts, type: UCOUNT_TIME_NAMESPACES);
68}
69
70/**
71 * clone_time_ns - Clone a time namespace
72 * @user_ns: User namespace which owns a new namespace.
73 * @old_ns: Namespace to clone
74 *
75 * Clone @old_ns and set the clone refcount to 1
76 *
77 * Return: The new namespace or ERR_PTR.
78 */
79static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
80 struct time_namespace *old_ns)
81{
82 struct time_namespace *ns;
83 struct ucounts *ucounts;
84 int err;
85
86 err = -ENOSPC;
87 ucounts = inc_time_namespaces(ns: user_ns);
88 if (!ucounts)
89 goto fail;
90
91 err = -ENOMEM;
92 ns = kzalloc(sizeof(*ns), GFP_KERNEL_ACCOUNT);
93 if (!ns)
94 goto fail_dec;
95
96 ns->vvar_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
97 if (!ns->vvar_page)
98 goto fail_free;
99
100 err = ns_common_init(ns);
101 if (err)
102 goto fail_free_page;
103
104 ns->ucounts = ucounts;
105 ns->user_ns = get_user_ns(ns: user_ns);
106 ns->offsets = old_ns->offsets;
107 ns->frozen_offsets = false;
108 ns_tree_add(ns);
109 return ns;
110
111fail_free_page:
112 __free_page(ns->vvar_page);
113fail_free:
114 kfree(objp: ns);
115fail_dec:
116 dec_time_namespaces(ucounts);
117fail:
118 return ERR_PTR(error: err);
119}
120
121/**
122 * copy_time_ns - Create timens_for_children from @old_ns
123 * @flags: Cloning flags
124 * @user_ns: User namespace which owns a new namespace.
125 * @old_ns: Namespace to clone
126 *
127 * If CLONE_NEWTIME specified in @flags, creates a new timens_for_children;
128 * adds a refcounter to @old_ns otherwise.
129 *
130 * Return: timens_for_children namespace or ERR_PTR.
131 */
132struct time_namespace *copy_time_ns(u64 flags,
133 struct user_namespace *user_ns, struct time_namespace *old_ns)
134{
135 if (!(flags & CLONE_NEWTIME))
136 return get_time_ns(ns: old_ns);
137
138 return clone_time_ns(user_ns, old_ns);
139}
140
141static struct timens_offset offset_from_ts(struct timespec64 off)
142{
143 struct timens_offset ret;
144
145 ret.sec = off.tv_sec;
146 ret.nsec = off.tv_nsec;
147
148 return ret;
149}
150
151/*
152 * A time namespace VVAR page has the same layout as the VVAR page which
153 * contains the system wide VDSO data.
154 *
155 * For a normal task the VVAR pages are installed in the normal ordering:
156 * VVAR
157 * PVCLOCK
158 * HVCLOCK
159 * TIMENS <- Not really required
160 *
161 * Now for a timens task the pages are installed in the following order:
162 * TIMENS
163 * PVCLOCK
164 * HVCLOCK
165 * VVAR
166 *
167 * The check for vdso_clock->clock_mode is in the unlikely path of
168 * the seq begin magic. So for the non-timens case most of the time
169 * 'seq' is even, so the branch is not taken.
170 *
171 * If 'seq' is odd, i.e. a concurrent update is in progress, the extra check
172 * for vdso_clock->clock_mode is a non-issue. The task is spin waiting for the
173 * update to finish and for 'seq' to become even anyway.
174 *
175 * Timens page has vdso_clock->clock_mode set to VDSO_CLOCKMODE_TIMENS which
176 * enforces the time namespace handling path.
177 */
178static void timens_setup_vdso_clock_data(struct vdso_clock *vc,
179 struct time_namespace *ns)
180{
181 struct timens_offset *offset = vc->offset;
182 struct timens_offset monotonic = offset_from_ts(off: ns->offsets.monotonic);
183 struct timens_offset boottime = offset_from_ts(off: ns->offsets.boottime);
184
185 vc->seq = 1;
186 vc->clock_mode = VDSO_CLOCKMODE_TIMENS;
187 offset[CLOCK_MONOTONIC] = monotonic;
188 offset[CLOCK_MONOTONIC_RAW] = monotonic;
189 offset[CLOCK_MONOTONIC_COARSE] = monotonic;
190 offset[CLOCK_BOOTTIME] = boottime;
191 offset[CLOCK_BOOTTIME_ALARM] = boottime;
192}
193
194struct page *find_timens_vvar_page(struct vm_area_struct *vma)
195{
196 if (likely(vma->vm_mm == current->mm))
197 return current->nsproxy->time_ns->vvar_page;
198
199 /*
200 * VM_PFNMAP | VM_IO protect .fault() handler from being called
201 * through interfaces like /proc/$pid/mem or
202 * process_vm_{readv,writev}() as long as there's no .access()
203 * in special_mapping_vmops().
204 * For more details check_vma_flags() and __access_remote_vm()
205 */
206
207 WARN(1, "vvar_page accessed remotely");
208
209 return NULL;
210}
211
212/*
213 * Protects possibly multiple offsets writers racing each other
214 * and tasks entering the namespace.
215 */
216static DEFINE_MUTEX(offset_lock);
217
218static void timens_set_vvar_page(struct task_struct *task,
219 struct time_namespace *ns)
220{
221 struct vdso_time_data *vdata;
222 struct vdso_clock *vc;
223 unsigned int i;
224
225 if (ns == &init_time_ns)
226 return;
227
228 /* Fast-path, taken by every task in namespace except the first. */
229 if (likely(ns->frozen_offsets))
230 return;
231
232 mutex_lock(&offset_lock);
233 /* Nothing to-do: vvar_page has been already initialized. */
234 if (ns->frozen_offsets)
235 goto out;
236
237 ns->frozen_offsets = true;
238 vdata = page_address(ns->vvar_page);
239 vc = vdata->clock_data;
240
241 for (i = 0; i < CS_BASES; i++)
242 timens_setup_vdso_clock_data(vc: &vc[i], ns);
243
244 if (IS_ENABLED(CONFIG_POSIX_AUX_CLOCKS)) {
245 for (i = 0; i < ARRAY_SIZE(vdata->aux_clock_data); i++)
246 timens_setup_vdso_clock_data(vc: &vdata->aux_clock_data[i], ns);
247 }
248
249out:
250 mutex_unlock(lock: &offset_lock);
251}
252
253void free_time_ns(struct time_namespace *ns)
254{
255 ns_tree_remove(ns);
256 dec_time_namespaces(ucounts: ns->ucounts);
257 put_user_ns(ns: ns->user_ns);
258 ns_common_free(ns);
259 __free_page(ns->vvar_page);
260 /* Concurrent nstree traversal depends on a grace period. */
261 kfree_rcu(ns, ns.ns_rcu);
262}
263
264static struct ns_common *timens_get(struct task_struct *task)
265{
266 struct time_namespace *ns = NULL;
267 struct nsproxy *nsproxy;
268
269 task_lock(p: task);
270 nsproxy = task->nsproxy;
271 if (nsproxy) {
272 ns = nsproxy->time_ns;
273 get_time_ns(ns);
274 }
275 task_unlock(p: task);
276
277 return ns ? &ns->ns : NULL;
278}
279
280static struct ns_common *timens_for_children_get(struct task_struct *task)
281{
282 struct time_namespace *ns = NULL;
283 struct nsproxy *nsproxy;
284
285 task_lock(p: task);
286 nsproxy = task->nsproxy;
287 if (nsproxy) {
288 ns = nsproxy->time_ns_for_children;
289 get_time_ns(ns);
290 }
291 task_unlock(p: task);
292
293 return ns ? &ns->ns : NULL;
294}
295
296static void timens_put(struct ns_common *ns)
297{
298 put_time_ns(ns: to_time_ns(ns));
299}
300
301void timens_commit(struct task_struct *tsk, struct time_namespace *ns)
302{
303 timens_set_vvar_page(task: tsk, ns);
304 vdso_join_timens(task: tsk, ns);
305}
306
307static int timens_install(struct nsset *nsset, struct ns_common *new)
308{
309 struct nsproxy *nsproxy = nsset->nsproxy;
310 struct time_namespace *ns = to_time_ns(ns: new);
311
312 if (!current_is_single_threaded())
313 return -EUSERS;
314
315 if (!ns_capable(ns: ns->user_ns, CAP_SYS_ADMIN) ||
316 !ns_capable(ns: nsset->cred->user_ns, CAP_SYS_ADMIN))
317 return -EPERM;
318
319 get_time_ns(ns);
320 put_time_ns(ns: nsproxy->time_ns);
321 nsproxy->time_ns = ns;
322
323 get_time_ns(ns);
324 put_time_ns(ns: nsproxy->time_ns_for_children);
325 nsproxy->time_ns_for_children = ns;
326 return 0;
327}
328
329void timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk)
330{
331 struct ns_common *nsc = &nsproxy->time_ns_for_children->ns;
332 struct time_namespace *ns = to_time_ns(ns: nsc);
333
334 /* create_new_namespaces() already incremented the ref counter */
335 if (nsproxy->time_ns == nsproxy->time_ns_for_children)
336 return;
337
338 get_time_ns(ns);
339 put_time_ns(ns: nsproxy->time_ns);
340 nsproxy->time_ns = ns;
341
342 timens_commit(tsk, ns);
343}
344
345static struct user_namespace *timens_owner(struct ns_common *ns)
346{
347 return to_time_ns(ns)->user_ns;
348}
349
350static void show_offset(struct seq_file *m, int clockid, struct timespec64 *ts)
351{
352 char *clock;
353
354 switch (clockid) {
355 case CLOCK_BOOTTIME:
356 clock = "boottime";
357 break;
358 case CLOCK_MONOTONIC:
359 clock = "monotonic";
360 break;
361 default:
362 clock = "unknown";
363 break;
364 }
365 seq_printf(m, fmt: "%-10s %10lld %9ld\n", clock, ts->tv_sec, ts->tv_nsec);
366}
367
368void proc_timens_show_offsets(struct task_struct *p, struct seq_file *m)
369{
370 struct ns_common *ns;
371 struct time_namespace *time_ns;
372
373 ns = timens_for_children_get(task: p);
374 if (!ns)
375 return;
376 time_ns = to_time_ns(ns);
377
378 show_offset(m, CLOCK_MONOTONIC, ts: &time_ns->offsets.monotonic);
379 show_offset(m, CLOCK_BOOTTIME, ts: &time_ns->offsets.boottime);
380 put_time_ns(ns: time_ns);
381}
382
383int proc_timens_set_offset(struct file *file, struct task_struct *p,
384 struct proc_timens_offset *offsets, int noffsets)
385{
386 struct ns_common *ns;
387 struct time_namespace *time_ns;
388 struct timespec64 tp;
389 int i, err;
390
391 ns = timens_for_children_get(task: p);
392 if (!ns)
393 return -ESRCH;
394 time_ns = to_time_ns(ns);
395
396 if (!file_ns_capable(file, ns: time_ns->user_ns, CAP_SYS_TIME)) {
397 put_time_ns(ns: time_ns);
398 return -EPERM;
399 }
400
401 for (i = 0; i < noffsets; i++) {
402 struct proc_timens_offset *off = &offsets[i];
403
404 switch (off->clockid) {
405 case CLOCK_MONOTONIC:
406 ktime_get_ts64(ts: &tp);
407 break;
408 case CLOCK_BOOTTIME:
409 ktime_get_boottime_ts64(ts: &tp);
410 break;
411 default:
412 err = -EINVAL;
413 goto out;
414 }
415
416 err = -ERANGE;
417
418 if (off->val.tv_sec > KTIME_SEC_MAX ||
419 off->val.tv_sec < -KTIME_SEC_MAX)
420 goto out;
421
422 tp = timespec64_add(lhs: tp, rhs: off->val);
423 /*
424 * KTIME_SEC_MAX is divided by 2 to be sure that KTIME_MAX is
425 * still unreachable.
426 */
427 if (tp.tv_sec < 0 || tp.tv_sec > KTIME_SEC_MAX / 2)
428 goto out;
429 }
430
431 mutex_lock(&offset_lock);
432 if (time_ns->frozen_offsets) {
433 err = -EACCES;
434 goto out_unlock;
435 }
436
437 err = 0;
438 /* Don't report errors after this line */
439 for (i = 0; i < noffsets; i++) {
440 struct proc_timens_offset *off = &offsets[i];
441 struct timespec64 *offset = NULL;
442
443 switch (off->clockid) {
444 case CLOCK_MONOTONIC:
445 offset = &time_ns->offsets.monotonic;
446 break;
447 case CLOCK_BOOTTIME:
448 offset = &time_ns->offsets.boottime;
449 break;
450 }
451
452 *offset = off->val;
453 }
454
455out_unlock:
456 mutex_unlock(lock: &offset_lock);
457out:
458 put_time_ns(ns: time_ns);
459
460 return err;
461}
462
463const struct proc_ns_operations timens_operations = {
464 .name = "time",
465 .get = timens_get,
466 .put = timens_put,
467 .install = timens_install,
468 .owner = timens_owner,
469};
470
471const struct proc_ns_operations timens_for_children_operations = {
472 .name = "time_for_children",
473 .real_ns_name = "time",
474 .get = timens_for_children_get,
475 .put = timens_put,
476 .install = timens_install,
477 .owner = timens_owner,
478};
479
480struct time_namespace init_time_ns = {
481 .ns = NS_COMMON_INIT(init_time_ns),
482 .user_ns = &init_user_ns,
483 .frozen_offsets = true,
484};
485
486void __init time_ns_init(void)
487{
488 ns_tree_add(&init_time_ns);
489}
490

source code of linux/kernel/time/namespace.c