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/mnt_namespace.h>
  28 #include <linux/completion.h>
  29 #include <linux/file.h>
  30 #include <linux/workqueue.h>
  31 #include <linux/security.h>
  32 #include <linux/mount.h>
  33 #include <linux/kernel.h>
  34 #include <linux/init.h>
  35 #include <linux/resource.h>
  36 #include <linux/notifier.h>
  37 #include <linux/suspend.h>
  38 #include <asm/uaccess.h>
  39
  40 extern int max_threads;
  41
  42 static struct workqueue_struct *khelper_wq;
  43
  44 #ifdef CONFIG_KMOD
  45
  46 /*
  47         modprobe_path is set via /proc/sys.
  48 */
  49 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  50
  51 /**
  52  * request_module - try to load a kernel module
  53  * @fmt:     printf style format string for the name of the module
  54  * @varargs: arguements as specified in the format string
  55  *
  56  * Load a module using the user mode module loader. The function returns
  57  * zero on success or a negative errno code on failure. Note that a
  58  * successful module load does not mean the module did not then unload
  59  * and exit on an error of its own. Callers must check that the service
  60  * they requested is now available not blindly invoke it.
  61  *
  62  * If module auto-loading support is disabled then this function
  63  * becomes a no-operation.
  64  */
  65 int request_module(const char *fmt, ...)
  66 {
  67         va_list args;
  68         char module_name[MODULE_NAME_LEN];
  69         unsigned int max_modprobes;
  70         int ret;
  71         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  72         static char *envp[] = { "HOME=/",
  73                                 "TERM=linux",
  74                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  75                                 NULL };
  76         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  77 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  78         static int kmod_loop_msg;
  79
  80         va_start(args, fmt);
  81         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  82         va_end(args);
  83         if (ret >= MODULE_NAME_LEN)
  84                 return -ENAMETOOLONG;
  85
  86         /* If modprobe needs a service that is in a module, we get a recursive
  87          * loop.  Limit the number of running kmod threads to max_threads/2 or
  88          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  89          * would be to run the parents of this process, counting how many times
  90          * kmod was invoked.  That would mean accessing the internals of the
  91          * process tables to get the command line, proc_pid_cmdline is static
  92          * and it is not worth changing the proc code just to handle this case.
  93          * KAO.
  94          *
  95          * "trace the ppid" is simple, but will fail if someone's
  96          * parent exits.  I think this is as good as it gets. --RR
  97          */
  98         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
  99         atomic_inc(&kmod_concurrent);
 100         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 101                 /* We may be blaming an innocent here, but unlikely */
 102                 if (kmod_loop_msg++ < 5)
 103                         printk(KERN_ERR
 104                                "request_module: runaway loop modprobe %s\n",
 105                                module_name);
 106                 atomic_dec(&kmod_concurrent);
 107                 return -ENOMEM;
 108         }
 109
 110         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 111         atomic_dec(&kmod_concurrent);
 112         return ret;
 113 }
 114 EXPORT_SYMBOL(request_module);
 115 #endif /* CONFIG_KMOD */
 116
 117 struct subprocess_info {
 118         struct work_struct work;
 119         struct completion *complete;
 120         char *path;
 121         char **argv;
 122         char **envp;
 123         struct key *ring;
 124         enum umh_wait wait;
 125         int retval;
 126         struct file *stdin;
 127         void (*cleanup)(char **argv, char **envp);
 128 };
 129
 130 /*
 131  * This is the task which runs the usermode application
 132  */
 133 static int ____call_usermodehelper(void *data)
 134 {
 135         struct subprocess_info *sub_info = data;
 136         struct key *new_session, *old_session;
 137         int retval;
 138
 139         /* Unblock all signals and set the session keyring. */
 140         new_session = key_get(sub_info->ring);
 141         spin_lock_irq(&current->sighand->siglock);
 142         old_session = __install_session_keyring(current, new_session);
 143         flush_signal_handlers(current, 1);
 144         sigemptyset(&current->blocked);
 145         recalc_sigpending();
 146         spin_unlock_irq(&current->sighand->siglock);
 147
 148         key_put(old_session);
 149
 150         /* Install input pipe when needed */
 151         if (sub_info->stdin) {
 152                 struct files_struct *f = current->files;
 153                 struct fdtable *fdt;
 154                 /* no races because files should be private here */
 155                 sys_close(0);
 156                 fd_install(0, sub_info->stdin);
 157                 spin_lock(&f->file_lock);
 158                 fdt = files_fdtable(f);
 159                 FD_SET(0, fdt->open_fds);
 160                 FD_CLR(0, fdt->close_on_exec);
 161                 spin_unlock(&f->file_lock);
 162
 163                 /* and disallow core files too */
 164                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 165         }
 166
 167         /* We can run anywhere, unlike our parent keventd(). */
 168         set_cpus_allowed(current, CPU_MASK_ALL);
 169
 170         /*
 171          * Our parent is keventd, which runs with elevated scheduling priority.
 172          * Avoid propagating that into the userspace child.
 173          */
 174         set_user_nice(current, 0);
 175
 176         retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);
 177
 178         /* Exec failed? */
 179         sub_info->retval = retval;
 180         do_exit(0);
 181 }
 182
 183 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 184 {
 185         if (info->cleanup)
 186                 (*info->cleanup)(info->argv, info->envp);
 187         kfree(info);
 188 }
 189 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 190
 191 /* Keventd can't block, but this (a child) can. */
 192 static int wait_for_helper(void *data)
 193 {
 194         struct subprocess_info *sub_info = data;
 195         pid_t pid;
 196
 197         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 198          * populate the status, but will return -ECHILD. */
 199         allow_signal(SIGCHLD);
 200
 201         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 202         if (pid < 0) {
 203                 sub_info->retval = pid;
 204         } else {
 205                 int ret;
 206
 207                 /*
 208                  * Normally it is bogus to call wait4() from in-kernel because
 209                  * wait4() wants to write the exit code to a userspace address.
 210                  * But wait_for_helper() always runs as keventd, and put_user()
 211                  * to a kernel address works OK for kernel threads, due to their
 212                  * having an mm_segment_t which spans the entire address space.
 213                  *
 214                  * Thus the __user pointer cast is valid here.
 215                  */
 216                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 217
 218                 /*
 219                  * If ret is 0, either ____call_usermodehelper failed and the
 220                  * real error code is already in sub_info->retval or
 221                  * sub_info->retval is 0 anyway, so don't mess with it then.
 222                  */
 223                 if (ret)
 224                         sub_info->retval = ret;
 225         }
 226
 227         if (sub_info->wait == UMH_NO_WAIT)
 228                 call_usermodehelper_freeinfo(sub_info);
 229         else
 230                 complete(sub_info->complete);
 231         return 0;
 232 }
 233
 234 /* This is run by khelper thread  */
 235 static void __call_usermodehelper(struct work_struct *work)
 236 {
 237         struct subprocess_info *sub_info =
 238                 container_of(work, struct subprocess_info, work);
 239         pid_t pid;
 240         enum umh_wait wait = sub_info->wait;
 241
 242         /* CLONE_VFORK: wait until the usermode helper has execve'd
 243          * successfully We need the data structures to stay around
 244          * until that is done.  */
 245         if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
 246                 pid = kernel_thread(wait_for_helper, sub_info,
 247                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 248         else
 249                 pid = kernel_thread(____call_usermodehelper, sub_info,
 250                                     CLONE_VFORK | SIGCHLD);
 251
 252         switch (wait) {
 253         case UMH_NO_WAIT:
 254                 break;
 255
 256         case UMH_WAIT_PROC:
 257                 if (pid > 0)
 258                         break;
 259                 sub_info->retval = pid;
 260                 /* FALLTHROUGH */
 261
 262         case UMH_WAIT_EXEC:
 263                 complete(sub_info->complete);
 264         }
 265 }
 266
 267 #ifdef CONFIG_PM
 268 /*
 269  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 270  * (used for preventing user land processes from being created after the user
 271  * land has been frozen during a system-wide hibernation or suspend operation).
 272  */
 273 static int usermodehelper_disabled;
 274
 275 /* Number of helpers running */
 276 static atomic_t running_helpers = ATOMIC_INIT(0);
 277
 278 /*
 279  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 280  * helpers to finish.
 281  */
 282 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 283
 284 /*
 285  * Time to wait for running_helpers to become zero before the setting of
 286  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 287  */
 288 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 289
 290 static int usermodehelper_pm_callback(struct notifier_block *nfb,
 291                                         unsigned long action,
 292                                         void *ignored)
 293 {
 294         long retval;
 295
 296         switch (action) {
 297         case PM_HIBERNATION_PREPARE:
 298         case PM_SUSPEND_PREPARE:
 299                 usermodehelper_disabled = 1;
 300                 smp_mb();
 301                 /*
 302                  * From now on call_usermodehelper_exec() won't start any new
 303                  * helpers, so it is sufficient if running_helpers turns out to
 304                  * be zero at one point (it may be increased later, but that
 305                  * doesn't matter).
 306                  */
 307                 retval = wait_event_timeout(running_helpers_waitq,
 308                                         atomic_read(&running_helpers) == 0,
 309                                         RUNNING_HELPERS_TIMEOUT);
 310                 if (retval) {
 311                         return NOTIFY_OK;
 312                 } else {
 313                         usermodehelper_disabled = 0;
 314                         return NOTIFY_BAD;
 315                 }
 316         case PM_POST_HIBERNATION:
 317         case PM_POST_SUSPEND:
 318                 usermodehelper_disabled = 0;
 319                 return NOTIFY_OK;
 320         }
 321
 322         return NOTIFY_DONE;
 323 }
 324
 325 static void helper_lock(void)
 326 {
 327         atomic_inc(&running_helpers);
 328         smp_mb__after_atomic_inc();
 329 }
 330
 331 static void helper_unlock(void)
 332 {
 333         if (atomic_dec_and_test(&running_helpers))
 334                 wake_up(&running_helpers_waitq);
 335 }
 336
 337 static void register_pm_notifier_callback(void)
 338 {
 339         pm_notifier(usermodehelper_pm_callback, 0);
 340 }
 341 #else /* CONFIG_PM */
 342 #define usermodehelper_disabled 0
 343
 344 static inline void helper_lock(void) {}
 345 static inline void helper_unlock(void) {}
 346 static inline void register_pm_notifier_callback(void) {}
 347 #endif /* CONFIG_PM */
 348
 349 /**
 350  * call_usermodehelper_setup - prepare to call a usermode helper
 351  * @path: path to usermode executable
 352  * @argv: arg vector for process
 353  * @envp: environment for process
 354  *
 355  * Returns either %NULL on allocation failure, or a subprocess_info
 356  * structure.  This should be passed to call_usermodehelper_exec to
 357  * exec the process and free the structure.
 358  */
 359 struct subprocess_info *call_usermodehelper_setup(char *path,
 360                                                   char **argv, char **envp)
 361 {
 362         struct subprocess_info *sub_info;
 363         sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
 364         if (!sub_info)
 365                 goto out;
 366
 367         INIT_WORK(&sub_info->work, __call_usermodehelper);
 368         sub_info->path = path;
 369         sub_info->argv = argv;
 370         sub_info->envp = envp;
 371
 372   out:
 373         return sub_info;
 374 }
 375 EXPORT_SYMBOL(call_usermodehelper_setup);
 376
 377 /**
 378  * call_usermodehelper_setkeys - set the session keys for usermode helper
 379  * @info: a subprocess_info returned by call_usermodehelper_setup
 380  * @session_keyring: the session keyring for the process
 381  */
 382 void call_usermodehelper_setkeys(struct subprocess_info *info,
 383                                  struct key *session_keyring)
 384 {
 385         info->ring = session_keyring;
 386 }
 387 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 388
 389 /**
 390  * call_usermodehelper_setcleanup - set a cleanup function
 391  * @info: a subprocess_info returned by call_usermodehelper_setup
 392  * @cleanup: a cleanup function
 393  *
 394  * The cleanup function is just befor ethe subprocess_info is about to
 395  * be freed.  This can be used for freeing the argv and envp.  The
 396  * Function must be runnable in either a process context or the
 397  * context in which call_usermodehelper_exec is called.
 398  */
 399 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 400                                     void (*cleanup)(char **argv, char **envp))
 401 {
 402         info->cleanup = cleanup;
 403 }
 404 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 405
 406 /**
 407  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 408  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 409  * @filp: set to the write-end of a pipe
 410  *
 411  * This constructs a pipe, and sets the read end to be the stdin of the
 412  * subprocess, and returns the write-end in *@filp.
 413  */
 414 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 415                                   struct file **filp)
 416 {
 417         struct file *f;
 418
 419         f = create_write_pipe();
 420         if (IS_ERR(f))
 421                 return PTR_ERR(f);
 422         *filp = f;
 423
 424         f = create_read_pipe(f);
 425         if (IS_ERR(f)) {
 426                 free_write_pipe(*filp);
 427                 return PTR_ERR(f);
 428         }
 429         sub_info->stdin = f;
 430
 431         return 0;
 432 }
 433 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 434
 435 /**
 436  * call_usermodehelper_exec - start a usermode application
 437  * @sub_info: information about the subprocessa
 438  * @wait: wait for the application to finish and return status.
 439  *        when -1 don't wait at all, but you get no useful error back when
 440  *        the program couldn't be exec'ed. This makes it safe to call
 441  *        from interrupt context.
 442  *
 443  * Runs a user-space application.  The application is started
 444  * asynchronously if wait is not set, and runs as a child of keventd.
 445  * (ie. it runs with full root capabilities).
 446  */
 447 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 448                              enum umh_wait wait)
 449 {
 450         DECLARE_COMPLETION_ONSTACK(done);
 451         int retval = 0;
 452
 453         helper_lock();
 454         if (sub_info->path[0] == '\0')
 455                 goto out;
 456
 457         if (!khelper_wq || usermodehelper_disabled) {
 458                 retval = -EBUSY;
 459                 goto out;
 460         }
 461
 462         sub_info->complete = &done;
 463         sub_info->wait = wait;
 464
 465         queue_work(khelper_wq, &sub_info->work);
 466         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 467                 goto unlock;
 468         wait_for_completion(&done);
 469         retval = sub_info->retval;
 470
 471 out:
 472         call_usermodehelper_freeinfo(sub_info);
 473 unlock:
 474         helper_unlock();
 475         return retval;
 476 }
 477 EXPORT_SYMBOL(call_usermodehelper_exec);
 478
 479 /**
 480  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 481  * @path: path to usermode executable
 482  * @argv: arg vector for process
 483  * @envp: environment for process
 484  * @filp: set to the write-end of a pipe
 485  *
 486  * This is a simple wrapper which executes a usermode-helper function
 487  * with a pipe as stdin.  It is implemented entirely in terms of
 488  * lower-level call_usermodehelper_* functions.
 489  */
 490 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 491                              struct file **filp)
 492 {
 493         struct subprocess_info *sub_info;
 494         int ret;
 495
 496         sub_info = call_usermodehelper_setup(path, argv, envp);
 497         if (sub_info == NULL)
 498                 return -ENOMEM;
 499
 500         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 501         if (ret < 0)
 502                 goto out;
 503
 504         return call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 505
 506   out:
 507         call_usermodehelper_freeinfo(sub_info);
 508         return ret;
 509 }
 510 EXPORT_SYMBOL(call_usermodehelper_pipe);
 511
 512 void __init usermodehelper_init(void)
 513 {
 514         khelper_wq = create_singlethread_workqueue("khelper");
 515         BUG_ON(!khelper_wq);
 516         register_pm_notifier_callback();
 517 }