kernel/time/namespace.c

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