kernel/umh.c

   1 /*
   2  * umh - the kernel usermode helper
   3  */
   4 #include <linux/module.h>
   5 #include <linux/sched.h>
   6 #include <linux/sched/task.h>
   7 #include <linux/binfmts.h>
   8 #include <linux/syscalls.h>
   9 #include <linux/unistd.h>
  10 #include <linux/kmod.h>
  11 #include <linux/slab.h>
  12 #include <linux/completion.h>
  13 #include <linux/cred.h>
  14 #include <linux/file.h>
  15 #include <linux/fdtable.h>
  16 #include <linux/workqueue.h>
  17 #include <linux/security.h>
  18 #include <linux/mount.h>
  19 #include <linux/kernel.h>
  20 #include <linux/init.h>
  21 #include <linux/resource.h>
  22 #include <linux/notifier.h>
  23 #include <linux/suspend.h>
  24 #include <linux/rwsem.h>
  25 #include <linux/ptrace.h>
  26 #include <linux/async.h>
  27 #include <linux/uaccess.h>
  28
  29 #include <trace/events/module.h>
  30
  31 #define CAP_BSET        (void *)1
  32 #define CAP_PI          (void *)2
  33
  34 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
  35 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
  36 static DEFINE_SPINLOCK(umh_sysctl_lock);
  37 static DECLARE_RWSEM(umhelper_sem);
  38
  39 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
  40 {
  41         if (info->cleanup)
  42                 (*info->cleanup)(info);
  43         kfree(info);
  44 }
  45
  46 static void umh_complete(struct subprocess_info *sub_info)
  47 {
  48         struct completion *comp = xchg(&sub_info->complete, NULL);
  49         /*
  50          * See call_usermodehelper_exec(). If xchg() returns NULL
  51          * we own sub_info, the UMH_KILLABLE caller has gone away
  52          * or the caller used UMH_NO_WAIT.
  53          */
  54         if (comp)
  55                 complete(comp);
  56         else
  57                 call_usermodehelper_freeinfo(sub_info);
  58 }
  59
  60 /*
  61  * This is the task which runs the usermode application
  62  */
  63 static int call_usermodehelper_exec_async(void *data)
  64 {
  65         struct subprocess_info *sub_info = data;
  66         struct cred *new;
  67         int retval;
  68
  69         spin_lock_irq(&current->sighand->siglock);
  70         flush_signal_handlers(current, 1);
  71         spin_unlock_irq(&current->sighand->siglock);
  72
  73         /*
  74          * Our parent (unbound workqueue) runs with elevated scheduling
  75          * priority. Avoid propagating that into the userspace child.
  76          */
  77         set_user_nice(current, 0);
  78
  79         retval = -ENOMEM;
  80         new = prepare_kernel_cred(current);
  81         if (!new)
  82                 goto out;
  83
  84         spin_lock(&umh_sysctl_lock);
  85         new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
  86         new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
  87                                              new->cap_inheritable);
  88         spin_unlock(&umh_sysctl_lock);
  89
  90         if (sub_info->init) {
  91                 retval = sub_info->init(sub_info, new);
  92                 if (retval) {
  93                         abort_creds(new);
  94                         goto out;
  95                 }
  96         }
  97
  98         commit_creds(new);
  99
 100         retval = do_execve(getname_kernel(sub_info->path),
 101                            (const char __user *const __user *)sub_info->argv,
 102                            (const char __user *const __user *)sub_info->envp);
 103 out:
 104         sub_info->retval = retval;
 105         /*
 106          * call_usermodehelper_exec_sync() will call umh_complete
 107          * if UHM_WAIT_PROC.
 108          */
 109         if (!(sub_info->wait & UMH_WAIT_PROC))
 110                 umh_complete(sub_info);
 111         if (!retval)
 112                 return 0;
 113         do_exit(0);
 114 }
 115
 116 /* Handles UMH_WAIT_PROC.  */
 117 static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
 118 {
 119         pid_t pid;
 120
 121         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 122         kernel_sigaction(SIGCHLD, SIG_DFL);
 123         pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
 124         if (pid < 0) {
 125                 sub_info->retval = pid;
 126         } else {
 127                 int ret = -ECHILD;
 128                 /*
 129                  * Normally it is bogus to call wait4() from in-kernel because
 130                  * wait4() wants to write the exit code to a userspace address.
 131                  * But call_usermodehelper_exec_sync() always runs as kernel
 132                  * thread (workqueue) and put_user() to a kernel address works
 133                  * OK for kernel threads, due to their having an mm_segment_t
 134                  * which spans the entire address space.
 135                  *
 136                  * Thus the __user pointer cast is valid here.
 137                  */
 138                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 139
 140                 /*
 141                  * If ret is 0, either call_usermodehelper_exec_async failed and
 142                  * the real error code is already in sub_info->retval or
 143                  * sub_info->retval is 0 anyway, so don't mess with it then.
 144                  */
 145                 if (ret)
 146                         sub_info->retval = ret;
 147         }
 148
 149         /* Restore default kernel sig handler */
 150         kernel_sigaction(SIGCHLD, SIG_IGN);
 151
 152         umh_complete(sub_info);
 153 }
 154
 155 /*
 156  * We need to create the usermodehelper kernel thread from a task that is affine
 157  * to an optimized set of CPUs (or nohz housekeeping ones) such that they
 158  * inherit a widest affinity irrespective of call_usermodehelper() callers with
 159  * possibly reduced affinity (eg: per-cpu workqueues). We don't want
 160  * usermodehelper targets to contend a busy CPU.
 161  *
 162  * Unbound workqueues provide such wide affinity and allow to block on
 163  * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
 164  *
 165  * Besides, workqueues provide the privilege level that caller might not have
 166  * to perform the usermodehelper request.
 167  *
 168  */
 169 static void call_usermodehelper_exec_work(struct work_struct *work)
 170 {
 171         struct subprocess_info *sub_info =
 172                 container_of(work, struct subprocess_info, work);
 173
 174         if (sub_info->wait & UMH_WAIT_PROC) {
 175                 call_usermodehelper_exec_sync(sub_info);
 176         } else {
 177                 pid_t pid;
 178                 /*
 179                  * Use CLONE_PARENT to reparent it to kthreadd; we do not
 180                  * want to pollute current->children, and we need a parent
 181                  * that always ignores SIGCHLD to ensure auto-reaping.
 182                  */
 183                 pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
 184                                     CLONE_PARENT | SIGCHLD);
 185                 if (pid < 0) {
 186                         sub_info->retval = pid;
 187                         umh_complete(sub_info);
 188                 }
 189         }
 190 }
 191
 192 /*
 193  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 194  * (used for preventing user land processes from being created after the user
 195  * land has been frozen during a system-wide hibernation or suspend operation).
 196  * Should always be manipulated under umhelper_sem acquired for write.
 197  */
 198 static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
 199
 200 /* Number of helpers running */
 201 static atomic_t running_helpers = ATOMIC_INIT(0);
 202
 203 /*
 204  * Wait queue head used by usermodehelper_disable() to wait for all running
 205  * helpers to finish.
 206  */
 207 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 208
 209 /*
 210  * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
 211  * to become 'false'.
 212  */
 213 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
 214
 215 /*
 216  * Time to wait for running_helpers to become zero before the setting of
 217  * usermodehelper_disabled in usermodehelper_disable() fails
 218  */
 219 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 220
 221 int usermodehelper_read_trylock(void)
 222 {
 223         DEFINE_WAIT(wait);
 224         int ret = 0;
 225
 226         down_read(&umhelper_sem);
 227         for (;;) {
 228                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 229                                 TASK_INTERRUPTIBLE);
 230                 if (!usermodehelper_disabled)
 231                         break;
 232
 233                 if (usermodehelper_disabled == UMH_DISABLED)
 234                         ret = -EAGAIN;
 235
 236                 up_read(&umhelper_sem);
 237
 238                 if (ret)
 239                         break;
 240
 241                 schedule();
 242                 try_to_freeze();
 243
 244                 down_read(&umhelper_sem);
 245         }
 246         finish_wait(&usermodehelper_disabled_waitq, &wait);
 247         return ret;
 248 }
 249 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
 250
 251 long usermodehelper_read_lock_wait(long timeout)
 252 {
 253         DEFINE_WAIT(wait);
 254
 255         if (timeout < 0)
 256                 return -EINVAL;
 257
 258         down_read(&umhelper_sem);
 259         for (;;) {
 260                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 261                                 TASK_UNINTERRUPTIBLE);
 262                 if (!usermodehelper_disabled)
 263                         break;
 264
 265                 up_read(&umhelper_sem);
 266
 267                 timeout = schedule_timeout(timeout);
 268                 if (!timeout)
 269                         break;
 270
 271                 down_read(&umhelper_sem);
 272         }
 273         finish_wait(&usermodehelper_disabled_waitq, &wait);
 274         return timeout;
 275 }
 276 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
 277
 278 void usermodehelper_read_unlock(void)
 279 {
 280         up_read(&umhelper_sem);
 281 }
 282 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
 283
 284 /**
 285  * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
 286  * @depth: New value to assign to usermodehelper_disabled.
 287  *
 288  * Change the value of usermodehelper_disabled (under umhelper_sem locked for
 289  * writing) and wakeup tasks waiting for it to change.
 290  */
 291 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
 292 {
 293         down_write(&umhelper_sem);
 294         usermodehelper_disabled = depth;
 295         wake_up(&usermodehelper_disabled_waitq);
 296         up_write(&umhelper_sem);
 297 }
 298
 299 /**
 300  * __usermodehelper_disable - Prevent new helpers from being started.
 301  * @depth: New value to assign to usermodehelper_disabled.
 302  *
 303  * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
 304  */
 305 int __usermodehelper_disable(enum umh_disable_depth depth)
 306 {
 307         long retval;
 308
 309         if (!depth)
 310                 return -EINVAL;
 311
 312         down_write(&umhelper_sem);
 313         usermodehelper_disabled = depth;
 314         up_write(&umhelper_sem);
 315
 316         /*
 317          * From now on call_usermodehelper_exec() won't start any new
 318          * helpers, so it is sufficient if running_helpers turns out to
 319          * be zero at one point (it may be increased later, but that
 320          * doesn't matter).
 321          */
 322         retval = wait_event_timeout(running_helpers_waitq,
 323                                         atomic_read(&running_helpers) == 0,
 324                                         RUNNING_HELPERS_TIMEOUT);
 325         if (retval)
 326                 return 0;
 327
 328         __usermodehelper_set_disable_depth(UMH_ENABLED);
 329         return -EAGAIN;
 330 }
 331
 332 static void helper_lock(void)
 333 {
 334         atomic_inc(&running_helpers);
 335         smp_mb__after_atomic();
 336 }
 337
 338 static void helper_unlock(void)
 339 {
 340         if (atomic_dec_and_test(&running_helpers))
 341                 wake_up(&running_helpers_waitq);
 342 }
 343
 344 /**
 345  * call_usermodehelper_setup - prepare to call a usermode helper
 346  * @path: path to usermode executable
 347  * @argv: arg vector for process
 348  * @envp: environment for process
 349  * @gfp_mask: gfp mask for memory allocation
 350  * @cleanup: a cleanup function
 351  * @init: an init function
 352  * @data: arbitrary context sensitive data
 353  *
 354  * Returns either %NULL on allocation failure, or a subprocess_info
 355  * structure.  This should be passed to call_usermodehelper_exec to
 356  * exec the process and free the structure.
 357  *
 358  * The init function is used to customize the helper process prior to
 359  * exec.  A non-zero return code causes the process to error out, exit,
 360  * and return the failure to the calling process
 361  *
 362  * The cleanup function is just before ethe subprocess_info is about to
 363  * be freed.  This can be used for freeing the argv and envp.  The
 364  * Function must be runnable in either a process context or the
 365  * context in which call_usermodehelper_exec is called.
 366  */
 367 struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
 368                 char **envp, gfp_t gfp_mask,
 369                 int (*init)(struct subprocess_info *info, struct cred *new),
 370                 void (*cleanup)(struct subprocess_info *info),
 371                 void *data)
 372 {
 373         struct subprocess_info *sub_info;
 374         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 375         if (!sub_info)
 376                 goto out;
 377
 378         INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
 379
 380 #ifdef CONFIG_STATIC_USERMODEHELPER
 381         sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
 382 #else
 383         sub_info->path = path;
 384 #endif
 385         sub_info->argv = argv;
 386         sub_info->envp = envp;
 387
 388         sub_info->cleanup = cleanup;
 389         sub_info->init = init;
 390         sub_info->data = data;
 391   out:
 392         return sub_info;
 393 }
 394 EXPORT_SYMBOL(call_usermodehelper_setup);
 395
 396 /**
 397  * call_usermodehelper_exec - start a usermode application
 398  * @sub_info: information about the subprocessa
 399  * @wait: wait for the application to finish and return status.
 400  *        when UMH_NO_WAIT don't wait at all, but you get no useful error back
 401  *        when the program couldn't be exec'ed. This makes it safe to call
 402  *        from interrupt context.
 403  *
 404  * Runs a user-space application.  The application is started
 405  * asynchronously if wait is not set, and runs as a child of system workqueues.
 406  * (ie. it runs with full root capabilities and optimized affinity).
 407  */
 408 int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 409 {
 410         DECLARE_COMPLETION_ONSTACK(done);
 411         int retval = 0;
 412
 413         if (!sub_info->path) {
 414                 call_usermodehelper_freeinfo(sub_info);
 415                 return -EINVAL;
 416         }
 417         helper_lock();
 418         if (usermodehelper_disabled) {
 419                 retval = -EBUSY;
 420                 goto out;
 421         }
 422
 423         /*
 424          * If there is no binary for us to call, then just return and get out of
 425          * here.  This allows us to set STATIC_USERMODEHELPER_PATH to "" and
 426          * disable all call_usermodehelper() calls.
 427          */
 428         if (strlen(sub_info->path) == 0)
 429                 goto out;
 430
 431         /*
 432          * Set the completion pointer only if there is a waiter.
 433          * This makes it possible to use umh_complete to free
 434          * the data structure in case of UMH_NO_WAIT.
 435          */
 436         sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
 437         sub_info->wait = wait;
 438
 439         queue_work(system_unbound_wq, &sub_info->work);
 440         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 441                 goto unlock;
 442
 443         if (wait & UMH_KILLABLE) {
 444                 retval = wait_for_completion_killable(&done);
 445                 if (!retval)
 446                         goto wait_done;
 447
 448                 /* umh_complete() will see NULL and free sub_info */
 449                 if (xchg(&sub_info->complete, NULL))
 450                         goto unlock;
 451                 /* fallthrough, umh_complete() was already called */
 452         }
 453
 454         wait_for_completion(&done);
 455 wait_done:
 456         retval = sub_info->retval;
 457 out:
 458         call_usermodehelper_freeinfo(sub_info);
 459 unlock:
 460         helper_unlock();
 461         return retval;
 462 }
 463 EXPORT_SYMBOL(call_usermodehelper_exec);
 464
 465 /**
 466  * call_usermodehelper() - prepare and start a usermode application
 467  * @path: path to usermode executable
 468  * @argv: arg vector for process
 469  * @envp: environment for process
 470  * @wait: wait for the application to finish and return status.
 471  *        when UMH_NO_WAIT don't wait at all, but you get no useful error back
 472  *        when the program couldn't be exec'ed. This makes it safe to call
 473  *        from interrupt context.
 474  *
 475  * This function is the equivalent to use call_usermodehelper_setup() and
 476  * call_usermodehelper_exec().
 477  */
 478 int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
 479 {
 480         struct subprocess_info *info;
 481         gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
 482
 483         info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
 484                                          NULL, NULL, NULL);
 485         if (info == NULL)
 486                 return -ENOMEM;
 487
 488         return call_usermodehelper_exec(info, wait);
 489 }
 490 EXPORT_SYMBOL(call_usermodehelper);
 491
 492 static int proc_cap_handler(struct ctl_table *table, int write,
 493                          void __user *buffer, size_t *lenp, loff_t *ppos)
 494 {
 495         struct ctl_table t;
 496         unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
 497         kernel_cap_t new_cap;
 498         int err, i;
 499
 500         if (write && (!capable(CAP_SETPCAP) ||
 501                       !capable(CAP_SYS_MODULE)))
 502                 return -EPERM;
 503
 504         /*
 505          * convert from the global kernel_cap_t to the ulong array to print to
 506          * userspace if this is a read.
 507          */
 508         spin_lock(&umh_sysctl_lock);
 509         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
 510                 if (table->data == CAP_BSET)
 511                         cap_array[i] = usermodehelper_bset.cap[i];
 512                 else if (table->data == CAP_PI)
 513                         cap_array[i] = usermodehelper_inheritable.cap[i];
 514                 else
 515                         BUG();
 516         }
 517         spin_unlock(&umh_sysctl_lock);
 518
 519         t = *table;
 520         t.data = &cap_array;
 521
 522         /*
 523          * actually read or write and array of ulongs from userspace.  Remember
 524          * these are least significant 32 bits first
 525          */
 526         err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
 527         if (err < 0)
 528                 return err;
 529
 530         /*
 531          * convert from the sysctl array of ulongs to the kernel_cap_t
 532          * internal representation
 533          */
 534         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
 535                 new_cap.cap[i] = cap_array[i];
 536
 537         /*
 538          * Drop everything not in the new_cap (but don't add things)
 539          */
 540         if (write) {
 541                 spin_lock(&umh_sysctl_lock);
 542                 if (table->data == CAP_BSET)
 543                         usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 544                 if (table->data == CAP_PI)
 545                         usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
 546                 spin_unlock(&umh_sysctl_lock);
 547         }
 548
 549         return 0;
 550 }
 551
 552 struct ctl_table usermodehelper_table[] = {
 553         {
 554                 .procname       = "bset",
 555                 .data           = CAP_BSET,
 556                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 557                 .mode           = 0600,
 558                 .proc_handler   = proc_cap_handler,
 559         },
 560         {
 561                 .procname       = "inheritable",
 562                 .data           = CAP_PI,
 563                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 564                 .mode           = 0600,
 565                 .proc_handler   = proc_cap_handler,
 566         },
 567         { }
 568 };