kernel/kmod.c

   1 /*
   2         kmod, the new module loader (replaces kerneld)
   3         Kirk Petersen
   4
   5         Reorganized not to be a daemon by Adam Richter, with guidance
   6         from Greg Zornetzer.
   7
   8         Modified to avoid chroot and file sharing problems.
   9         Mikael Pettersson
  10
  11         Limit the concurrent number of kmod modprobes to catch loops from
  12         "modprobe needs a service that is in a module".
  13         Keith Owens <kaos@ocs.com.au> December 1999
  14
  15         Unblock all signals when we exec a usermode process.
  16         Shuu Yamaguchi <shuu@wondernetworkresources.com> December 2000
  17
  18         call_usermodehelper wait flag, and remove exec_usermodehelper.
  19         Rusty Russell <rusty@rustcorp.com.au>  Jan 2003
  20 */
  21 #include <linux/module.h>
  22 #include <linux/sched.h>
  23 #include <linux/syscalls.h>
  24 #include <linux/unistd.h>
  25 #include <linux/kmod.h>
  26 #include <linux/slab.h>
  27 #include <linux/completion.h>
  28 #include <linux/cred.h>
  29 #include <linux/file.h>
  30 #include <linux/fdtable.h>
  31 #include <linux/workqueue.h>
  32 #include <linux/security.h>
  33 #include <linux/mount.h>
  34 #include <linux/kernel.h>
  35 #include <linux/init.h>
  36 #include <linux/resource.h>
  37 #include <linux/notifier.h>
  38 #include <linux/suspend.h>
  39 #include <linux/rwsem.h>
  40 #include <asm/uaccess.h>
  41
  42 #include <trace/events/module.h>
  43
  44 extern int max_threads;
  45
  46 static struct workqueue_struct *khelper_wq;
  47
  48 #define CAP_BSET        (void *)1
  49 #define CAP_PI          (void *)2
  50
  51 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
  52 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
  53 static DEFINE_SPINLOCK(umh_sysctl_lock);
  54 static DECLARE_RWSEM(umhelper_sem);
  55
  56 #ifdef CONFIG_MODULES
  57
  58 /*
  59         modprobe_path is set via /proc/sys.
  60 */
  61 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  62
  63 static void free_modprobe_argv(struct subprocess_info *info)
  64 {
  65         kfree(info->argv[3]); /* check call_modprobe() */
  66         kfree(info->argv);
  67 }
  68
  69 static int call_modprobe(char *module_name, int wait)
  70 {
  71         static char *envp[] = {
  72                 "HOME=/",
  73                 "TERM=linux",
  74                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  75                 NULL
  76         };
  77
  78         char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
  79         if (!argv)
  80                 goto out;
  81
  82         module_name = kstrdup(module_name, GFP_KERNEL);
  83         if (!module_name)
  84                 goto free_argv;
  85
  86         argv[0] = modprobe_path;
  87         argv[1] = "-q";
  88         argv[2] = "--";
  89         argv[3] = module_name;  /* check free_modprobe_argv() */
  90         argv[4] = NULL;
  91
  92         return call_usermodehelper_fns(modprobe_path, argv, envp,
  93                 wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
  94 free_argv:
  95         kfree(argv);
  96 out:
  97         return -ENOMEM;
  98 }
  99
 100 /**
 101  * __request_module - try to load a kernel module
 102  * @wait: wait (or not) for the operation to complete
 103  * @fmt: printf style format string for the name of the module
 104  * @...: arguments as specified in the format string
 105  *
 106  * Load a module using the user mode module loader. The function returns
 107  * zero on success or a negative errno code on failure. Note that a
 108  * successful module load does not mean the module did not then unload
 109  * and exit on an error of its own. Callers must check that the service
 110  * they requested is now available not blindly invoke it.
 111  *
 112  * If module auto-loading support is disabled then this function
 113  * becomes a no-operation.
 114  */
 115 int __request_module(bool wait, const char *fmt, ...)
 116 {
 117         va_list args;
 118         char module_name[MODULE_NAME_LEN];
 119         unsigned int max_modprobes;
 120         int ret;
 121         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
 122 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
 123         static int kmod_loop_msg;
 124
 125         va_start(args, fmt);
 126         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
 127         va_end(args);
 128         if (ret >= MODULE_NAME_LEN)
 129                 return -ENAMETOOLONG;
 130
 131         ret = security_kernel_module_request(module_name);
 132         if (ret)
 133                 return ret;
 134
 135         /* If modprobe needs a service that is in a module, we get a recursive
 136          * loop.  Limit the number of running kmod threads to max_threads/2 or
 137          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 138          * would be to run the parents of this process, counting how many times
 139          * kmod was invoked.  That would mean accessing the internals of the
 140          * process tables to get the command line, proc_pid_cmdline is static
 141          * and it is not worth changing the proc code just to handle this case.
 142          * KAO.
 143          *
 144          * "trace the ppid" is simple, but will fail if someone's
 145          * parent exits.  I think this is as good as it gets. --RR
 146          */
 147         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 148         atomic_inc(&kmod_concurrent);
 149         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 150                 /* We may be blaming an innocent here, but unlikely */
 151                 if (kmod_loop_msg < 5) {
 152                         printk(KERN_ERR
 153                                "request_module: runaway loop modprobe %s\n",
 154                                module_name);
 155                         kmod_loop_msg++;
 156                 }
 157                 atomic_dec(&kmod_concurrent);
 158                 return -ENOMEM;
 159         }
 160
 161         trace_module_request(module_name, wait, _RET_IP_);
 162
 163         ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 164
 165         atomic_dec(&kmod_concurrent);
 166         return ret;
 167 }
 168 EXPORT_SYMBOL(__request_module);
 169 #endif /* CONFIG_MODULES */
 170
 171 /*
 172  * This is the task which runs the usermode application
 173  */
 174 static int ____call_usermodehelper(void *data)
 175 {
 176         struct subprocess_info *sub_info = data;
 177         struct cred *new;
 178         int retval;
 179
 180         spin_lock_irq(&current->sighand->siglock);
 181         flush_signal_handlers(current, 1);
 182         spin_unlock_irq(&current->sighand->siglock);
 183
 184         /* We can run anywhere, unlike our parent keventd(). */
 185         set_cpus_allowed_ptr(current, cpu_all_mask);
 186
 187         /*
 188          * Our parent is keventd, which runs with elevated scheduling priority.
 189          * Avoid propagating that into the userspace child.
 190          */
 191         set_user_nice(current, 0);
 192
 193         retval = -ENOMEM;
 194         new = prepare_kernel_cred(current);
 195         if (!new)
 196                 goto fail;
 197
 198         spin_lock(&umh_sysctl_lock);
 199         new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
 200         new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
 201                                              new->cap_inheritable);
 202         spin_unlock(&umh_sysctl_lock);
 203
 204         if (sub_info->init) {
 205                 retval = sub_info->init(sub_info, new);
 206                 if (retval) {
 207                         abort_creds(new);
 208                         goto fail;
 209                 }
 210         }
 211
 212         commit_creds(new);
 213
 214         retval = kernel_execve(sub_info->path,
 215                                (const char *const *)sub_info->argv,
 216                                (const char *const *)sub_info->envp);
 217
 218         /* Exec failed? */
 219 fail:
 220         sub_info->retval = retval;
 221         return 0;
 222 }
 223
 224 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 225 {
 226         if (info->cleanup)
 227                 (*info->cleanup)(info);
 228         kfree(info);
 229 }
 230 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 231
 232 static void umh_complete(struct subprocess_info *sub_info)
 233 {
 234         struct completion *comp = xchg(&sub_info->complete, NULL);
 235         /*
 236          * See call_usermodehelper_exec(). If xchg() returns NULL
 237          * we own sub_info, the UMH_KILLABLE caller has gone away.
 238          */
 239         if (comp)
 240                 complete(comp);
 241         else
 242                 call_usermodehelper_freeinfo(sub_info);
 243 }
 244
 245 /* Keventd can't block, but this (a child) can. */
 246 static int wait_for_helper(void *data)
 247 {
 248         struct subprocess_info *sub_info = data;
 249         pid_t pid;
 250
 251         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 252         spin_lock_irq(&current->sighand->siglock);
 253         current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
 254         spin_unlock_irq(&current->sighand->siglock);
 255
 256         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 257         if (pid < 0) {
 258                 sub_info->retval = pid;
 259         } else {
 260                 int ret = -ECHILD;
 261                 /*
 262                  * Normally it is bogus to call wait4() from in-kernel because
 263                  * wait4() wants to write the exit code to a userspace address.
 264                  * But wait_for_helper() always runs as keventd, and put_user()
 265                  * to a kernel address works OK for kernel threads, due to their
 266                  * having an mm_segment_t which spans the entire address space.
 267                  *
 268                  * Thus the __user pointer cast is valid here.
 269                  */
 270                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 271
 272                 /*
 273                  * If ret is 0, either ____call_usermodehelper failed and the
 274                  * real error code is already in sub_info->retval or
 275                  * sub_info->retval is 0 anyway, so don't mess with it then.
 276                  */
 277                 if (ret)
 278                         sub_info->retval = ret;
 279         }
 280
 281         umh_complete(sub_info);
 282         return 0;
 283 }
 284
 285 /* This is run by khelper thread  */
 286 static void __call_usermodehelper(struct work_struct *work)
 287 {
 288         struct subprocess_info *sub_info =
 289                 container_of(work, struct subprocess_info, work);
 290         int wait = sub_info->wait & ~UMH_KILLABLE;
 291         pid_t pid;
 292
 293         /* CLONE_VFORK: wait until the usermode helper has execve'd
 294          * successfully We need the data structures to stay around
 295          * until that is done.  */
 296         if (wait == UMH_WAIT_PROC)
 297                 pid = kernel_thread(wait_for_helper, sub_info,
 298                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 299         else
 300                 pid = kernel_thread(____call_usermodehelper, sub_info,
 301                                     CLONE_VFORK | SIGCHLD);
 302
 303         switch (wait) {
 304         case UMH_NO_WAIT:
 305                 call_usermodehelper_freeinfo(sub_info);
 306                 break;
 307
 308         case UMH_WAIT_PROC:
 309                 if (pid > 0)
 310                         break;
 311                 /* FALLTHROUGH */
 312         case UMH_WAIT_EXEC:
 313                 if (pid < 0)
 314                         sub_info->retval = pid;
 315                 umh_complete(sub_info);
 316         }
 317 }
 318
 319 /*
 320  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 321  * (used for preventing user land processes from being created after the user
 322  * land has been frozen during a system-wide hibernation or suspend operation).
 323  * Should always be manipulated under umhelper_sem acquired for write.
 324  */
 325 static int usermodehelper_disabled = 1;
 326
 327 /* Number of helpers running */
 328 static atomic_t running_helpers = ATOMIC_INIT(0);
 329
 330 /*
 331  * Wait queue head used by usermodehelper_disable() to wait for all running
 332  * helpers to finish.
 333  */
 334 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 335
 336 /*
 337  * Time to wait for running_helpers to become zero before the setting of
 338  * usermodehelper_disabled in usermodehelper_disable() fails
 339  */
 340 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 341
 342 void read_lock_usermodehelper(void)
 343 {
 344         down_read(&umhelper_sem);
 345 }
 346 EXPORT_SYMBOL_GPL(read_lock_usermodehelper);
 347
 348 void read_unlock_usermodehelper(void)
 349 {
 350         up_read(&umhelper_sem);
 351 }
 352 EXPORT_SYMBOL_GPL(read_unlock_usermodehelper);
 353
 354 /**
 355  * usermodehelper_disable - prevent new helpers from being started
 356  */
 357 int usermodehelper_disable(void)
 358 {
 359         long retval;
 360
 361         down_write(&umhelper_sem);
 362         usermodehelper_disabled = 1;
 363         up_write(&umhelper_sem);
 364
 365         /*
 366          * From now on call_usermodehelper_exec() won't start any new
 367          * helpers, so it is sufficient if running_helpers turns out to
 368          * be zero at one point (it may be increased later, but that
 369          * doesn't matter).
 370          */
 371         retval = wait_event_timeout(running_helpers_waitq,
 372                                         atomic_read(&running_helpers) == 0,
 373                                         RUNNING_HELPERS_TIMEOUT);
 374         if (retval)
 375                 return 0;
 376
 377         down_write(&umhelper_sem);
 378         usermodehelper_disabled = 0;
 379         up_write(&umhelper_sem);
 380         return -EAGAIN;
 381 }
 382
 383 /**
 384  * usermodehelper_enable - allow new helpers to be started again
 385  */
 386 void usermodehelper_enable(void)
 387 {
 388         down_write(&umhelper_sem);
 389         usermodehelper_disabled = 0;
 390         up_write(&umhelper_sem);
 391 }
 392
 393 /**
 394  * usermodehelper_is_disabled - check if new helpers are allowed to be started
 395  */
 396 bool usermodehelper_is_disabled(void)
 397 {
 398         return usermodehelper_disabled;
 399 }
 400 EXPORT_SYMBOL_GPL(usermodehelper_is_disabled);
 401
 402 static void helper_lock(void)
 403 {
 404         atomic_inc(&running_helpers);
 405         smp_mb__after_atomic_inc();
 406 }
 407
 408 static void helper_unlock(void)
 409 {
 410         if (atomic_dec_and_test(&running_helpers))
 411                 wake_up(&running_helpers_waitq);
 412 }
 413
 414 /**
 415  * call_usermodehelper_setup - prepare to call a usermode helper
 416  * @path: path to usermode executable
 417  * @argv: arg vector for process
 418  * @envp: environment for process
 419  * @gfp_mask: gfp mask for memory allocation
 420  *
 421  * Returns either %NULL on allocation failure, or a subprocess_info
 422  * structure.  This should be passed to call_usermodehelper_exec to
 423  * exec the process and free the structure.
 424  */
 425 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 426                                                   char **envp, gfp_t gfp_mask)
 427 {
 428         struct subprocess_info *sub_info;
 429         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 430         if (!sub_info)
 431                 goto out;
 432
 433         INIT_WORK(&sub_info->work, __call_usermodehelper);
 434         sub_info->path = path;
 435         sub_info->argv = argv;
 436         sub_info->envp = envp;
 437   out:
 438         return sub_info;
 439 }
 440 EXPORT_SYMBOL(call_usermodehelper_setup);
 441
 442 /**
 443  * call_usermodehelper_setfns - set a cleanup/init function
 444  * @info: a subprocess_info returned by call_usermodehelper_setup
 445  * @cleanup: a cleanup function
 446  * @init: an init function
 447  * @data: arbitrary context sensitive data
 448  *
 449  * The init function is used to customize the helper process prior to
 450  * exec.  A non-zero return code causes the process to error out, exit,
 451  * and return the failure to the calling process
 452  *
 453  * The cleanup function is just before ethe subprocess_info is about to
 454  * be freed.  This can be used for freeing the argv and envp.  The
 455  * Function must be runnable in either a process context or the
 456  * context in which call_usermodehelper_exec is called.
 457  */
 458 void call_usermodehelper_setfns(struct subprocess_info *info,
 459                     int (*init)(struct subprocess_info *info, struct cred *new),
 460                     void (*cleanup)(struct subprocess_info *info),
 461                     void *data)
 462 {
 463         info->cleanup = cleanup;
 464         info->init = init;
 465         info->data = data;
 466 }
 467 EXPORT_SYMBOL(call_usermodehelper_setfns);
 468
 469 /**
 470  * call_usermodehelper_exec - start a usermode application
 471  * @sub_info: information about the subprocessa
 472  * @wait: wait for the application to finish and return status.
 473  *        when -1 don't wait at all, but you get no useful error back when
 474  *        the program couldn't be exec'ed. This makes it safe to call
 475  *        from interrupt context.
 476  *
 477  * Runs a user-space application.  The application is started
 478  * asynchronously if wait is not set, and runs as a child of keventd.
 479  * (ie. it runs with full root capabilities).
 480  */
 481 int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 482 {
 483         DECLARE_COMPLETION_ONSTACK(done);
 484         int retval = 0;
 485
 486         helper_lock();
 487         if (sub_info->path[0] == '\0')
 488                 goto out;
 489
 490         if (!khelper_wq || usermodehelper_disabled) {
 491                 retval = -EBUSY;
 492                 goto out;
 493         }
 494
 495         sub_info->complete = &done;
 496         sub_info->wait = wait;
 497
 498         queue_work(khelper_wq, &sub_info->work);
 499         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 500                 goto unlock;
 501
 502         if (wait & UMH_KILLABLE) {
 503                 retval = wait_for_completion_killable(&done);
 504                 if (!retval)
 505                         goto wait_done;
 506
 507                 /* umh_complete() will see NULL and free sub_info */
 508                 if (xchg(&sub_info->complete, NULL))
 509                         goto unlock;
 510                 /* fallthrough, umh_complete() was already called */
 511         }
 512
 513         wait_for_completion(&done);
 514 wait_done:
 515         retval = sub_info->retval;
 516 out:
 517         call_usermodehelper_freeinfo(sub_info);
 518 unlock:
 519         helper_unlock();
 520         return retval;
 521 }
 522 EXPORT_SYMBOL(call_usermodehelper_exec);
 523
 524 static int proc_cap_handler(struct ctl_table *table, int write,
 525                          void __user *buffer, size_t *lenp, loff_t *ppos)
 526 {
 527         struct ctl_table t;
 528         unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
 529         kernel_cap_t new_cap;
 530         int err, i;
 531
 532         if (write && (!capable(CAP_SETPCAP) ||
 533                       !capable(CAP_SYS_MODULE)))
 534                 return -EPERM;
 535
 536         /*
 537          * convert from the global kernel_cap_t to the ulong array to print to
 538          * userspace if this is a read.
 539          */
 540         spin_lock(&umh_sysctl_lock);
 541         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
 542                 if (table->data == CAP_BSET)
 543                         cap_array[i] = usermodehelper_bset.cap[i];
 544                 else if (table->data == CAP_PI)
 545                         cap_array[i] = usermodehelper_inheritable.cap[i];
 546                 else
 547                         BUG();
 548         }
 549         spin_unlock(&umh_sysctl_lock);
 550
 551         t = *table;
 552         t.data = &cap_array;
 553
 554         /*
 555          * actually read or write and array of ulongs from userspace.  Remember
 556          * these are least significant 32 bits first
 557          */
 558         err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
 559         if (err < 0)
 560                 return err;
 561
 562         /*
 563          * convert from the sysctl array of ulongs to the kernel_cap_t
 564          * internal representation
 565          */
 566         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
 567                 new_cap.cap[i] = cap_array[i];
 568
 569         /*
 570          * Drop everything not in the new_cap (but don't add things)
 571          */
 572         spin_lock(&umh_sysctl_lock);
 573         if (write) {
 574                 if (table->data == CAP_BSET)
 575                         usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 576                 if (table->data == CAP_PI)
 577                         usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
 578         }
 579         spin_unlock(&umh_sysctl_lock);
 580
 581         return 0;
 582 }
 583
 584 struct ctl_table usermodehelper_table[] = {
 585         {
 586                 .procname       = "bset",
 587                 .data           = CAP_BSET,
 588                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 589                 .mode           = 0600,
 590                 .proc_handler   = proc_cap_handler,
 591         },
 592         {
 593                 .procname       = "inheritable",
 594                 .data           = CAP_PI,
 595                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 596                 .mode           = 0600,
 597                 .proc_handler   = proc_cap_handler,
 598         },
 599         { }
 600 };
 601
 602 void __init usermodehelper_init(void)
 603 {
 604         khelper_wq = create_singlethread_workqueue("khelper");
 605         BUG_ON(!khelper_wq);
 606 }