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 = -EPERM;
 177         if (current->fs->root)
 178                 retval = kernel_execve(sub_info->path,
 179                                 sub_info->argv, sub_info->envp);
 180
 181         /* Exec failed? */
 182         sub_info->retval = retval;
 183         do_exit(0);
 184 }
 185
 186 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 187 {
 188         if (info->cleanup)
 189                 (*info->cleanup)(info->argv, info->envp);
 190         kfree(info);
 191 }
 192 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 193
 194 /* Keventd can't block, but this (a child) can. */
 195 static int wait_for_helper(void *data)
 196 {
 197         struct subprocess_info *sub_info = data;
 198         pid_t pid;
 199
 200         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 201          * populate the status, but will return -ECHILD. */
 202         allow_signal(SIGCHLD);
 203
 204         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 205         if (pid < 0) {
 206                 sub_info->retval = pid;
 207         } else {
 208                 int ret;
 209
 210                 /*
 211                  * Normally it is bogus to call wait4() from in-kernel because
 212                  * wait4() wants to write the exit code to a userspace address.
 213                  * But wait_for_helper() always runs as keventd, and put_user()
 214                  * to a kernel address works OK for kernel threads, due to their
 215                  * having an mm_segment_t which spans the entire address space.
 216                  *
 217                  * Thus the __user pointer cast is valid here.
 218                  */
 219                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 220
 221                 /*
 222                  * If ret is 0, either ____call_usermodehelper failed and the
 223                  * real error code is already in sub_info->retval or
 224                  * sub_info->retval is 0 anyway, so don't mess with it then.
 225                  */
 226                 if (ret)
 227                         sub_info->retval = ret;
 228         }
 229
 230         if (sub_info->wait == UMH_NO_WAIT)
 231                 call_usermodehelper_freeinfo(sub_info);
 232         else
 233                 complete(sub_info->complete);
 234         return 0;
 235 }
 236
 237 /* This is run by khelper thread  */
 238 static void __call_usermodehelper(struct work_struct *work)
 239 {
 240         struct subprocess_info *sub_info =
 241                 container_of(work, struct subprocess_info, work);
 242         pid_t pid;
 243         enum umh_wait wait = sub_info->wait;
 244
 245         /* CLONE_VFORK: wait until the usermode helper has execve'd
 246          * successfully We need the data structures to stay around
 247          * until that is done.  */
 248         if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
 249                 pid = kernel_thread(wait_for_helper, sub_info,
 250                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 251         else
 252                 pid = kernel_thread(____call_usermodehelper, sub_info,
 253                                     CLONE_VFORK | SIGCHLD);
 254
 255         switch (wait) {
 256         case UMH_NO_WAIT:
 257                 break;
 258
 259         case UMH_WAIT_PROC:
 260                 if (pid > 0)
 261                         break;
 262                 sub_info->retval = pid;
 263                 /* FALLTHROUGH */
 264
 265         case UMH_WAIT_EXEC:
 266                 complete(sub_info->complete);
 267         }
 268 }
 269
 270 #ifdef CONFIG_PM
 271 /*
 272  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 273  * (used for preventing user land processes from being created after the user
 274  * land has been frozen during a system-wide hibernation or suspend operation).
 275  */
 276 static int usermodehelper_disabled;
 277
 278 /* Number of helpers running */
 279 static atomic_t running_helpers = ATOMIC_INIT(0);
 280
 281 /*
 282  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 283  * helpers to finish.
 284  */
 285 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 286
 287 /*
 288  * Time to wait for running_helpers to become zero before the setting of
 289  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 290  */
 291 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 292
 293 static int usermodehelper_pm_callback(struct notifier_block *nfb,
 294                                         unsigned long action,
 295                                         void *ignored)
 296 {
 297         long retval;
 298
 299         switch (action) {
 300         case PM_HIBERNATION_PREPARE:
 301         case PM_SUSPEND_PREPARE:
 302                 usermodehelper_disabled = 1;
 303                 smp_mb();
 304                 /*
 305                  * From now on call_usermodehelper_exec() won't start any new
 306                  * helpers, so it is sufficient if running_helpers turns out to
 307                  * be zero at one point (it may be increased later, but that
 308                  * doesn't matter).
 309                  */
 310                 retval = wait_event_timeout(running_helpers_waitq,
 311                                         atomic_read(&running_helpers) == 0,
 312                                         RUNNING_HELPERS_TIMEOUT);
 313                 if (retval) {
 314                         return NOTIFY_OK;
 315                 } else {
 316                         usermodehelper_disabled = 0;
 317                         return NOTIFY_BAD;
 318                 }
 319         case PM_POST_HIBERNATION:
 320         case PM_POST_SUSPEND:
 321                 usermodehelper_disabled = 0;
 322                 return NOTIFY_OK;
 323         }
 324
 325         return NOTIFY_DONE;
 326 }
 327
 328 static void helper_lock(void)
 329 {
 330         atomic_inc(&running_helpers);
 331         smp_mb__after_atomic_inc();
 332 }
 333
 334 static void helper_unlock(void)
 335 {
 336         if (atomic_dec_and_test(&running_helpers))
 337                 wake_up(&running_helpers_waitq);
 338 }
 339
 340 static void register_pm_notifier_callback(void)
 341 {
 342         pm_notifier(usermodehelper_pm_callback, 0);
 343 }
 344 #else /* CONFIG_PM */
 345 #define usermodehelper_disabled 0
 346
 347 static inline void helper_lock(void) {}
 348 static inline void helper_unlock(void) {}
 349 static inline void register_pm_notifier_callback(void) {}
 350 #endif /* CONFIG_PM */
 351
 352 /**
 353  * call_usermodehelper_setup - prepare to call a usermode helper
 354  * @path: path to usermode executable
 355  * @argv: arg vector for process
 356  * @envp: environment for process
 357  *
 358  * Returns either %NULL on allocation failure, or a subprocess_info
 359  * structure.  This should be passed to call_usermodehelper_exec to
 360  * exec the process and free the structure.
 361  */
 362 struct subprocess_info *call_usermodehelper_setup(char *path,
 363                                                   char **argv, char **envp)
 364 {
 365         struct subprocess_info *sub_info;
 366         sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
 367         if (!sub_info)
 368                 goto out;
 369
 370         INIT_WORK(&sub_info->work, __call_usermodehelper);
 371         sub_info->path = path;
 372         sub_info->argv = argv;
 373         sub_info->envp = envp;
 374
 375   out:
 376         return sub_info;
 377 }
 378 EXPORT_SYMBOL(call_usermodehelper_setup);
 379
 380 /**
 381  * call_usermodehelper_setkeys - set the session keys for usermode helper
 382  * @info: a subprocess_info returned by call_usermodehelper_setup
 383  * @session_keyring: the session keyring for the process
 384  */
 385 void call_usermodehelper_setkeys(struct subprocess_info *info,
 386                                  struct key *session_keyring)
 387 {
 388         info->ring = session_keyring;
 389 }
 390 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 391
 392 /**
 393  * call_usermodehelper_setcleanup - set a cleanup function
 394  * @info: a subprocess_info returned by call_usermodehelper_setup
 395  * @cleanup: a cleanup function
 396  *
 397  * The cleanup function is just befor ethe subprocess_info is about to
 398  * be freed.  This can be used for freeing the argv and envp.  The
 399  * Function must be runnable in either a process context or the
 400  * context in which call_usermodehelper_exec is called.
 401  */
 402 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 403                                     void (*cleanup)(char **argv, char **envp))
 404 {
 405         info->cleanup = cleanup;
 406 }
 407 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 408
 409 /**
 410  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 411  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 412  * @filp: set to the write-end of a pipe
 413  *
 414  * This constructs a pipe, and sets the read end to be the stdin of the
 415  * subprocess, and returns the write-end in *@filp.
 416  */
 417 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 418                                   struct file **filp)
 419 {
 420         struct file *f;
 421
 422         f = create_write_pipe();
 423         if (IS_ERR(f))
 424                 return PTR_ERR(f);
 425         *filp = f;
 426
 427         f = create_read_pipe(f);
 428         if (IS_ERR(f)) {
 429                 free_write_pipe(*filp);
 430                 return PTR_ERR(f);
 431         }
 432         sub_info->stdin = f;
 433
 434         return 0;
 435 }
 436 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 437
 438 /**
 439  * call_usermodehelper_exec - start a usermode application
 440  * @sub_info: information about the subprocessa
 441  * @wait: wait for the application to finish and return status.
 442  *        when -1 don't wait at all, but you get no useful error back when
 443  *        the program couldn't be exec'ed. This makes it safe to call
 444  *        from interrupt context.
 445  *
 446  * Runs a user-space application.  The application is started
 447  * asynchronously if wait is not set, and runs as a child of keventd.
 448  * (ie. it runs with full root capabilities).
 449  */
 450 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 451                              enum umh_wait wait)
 452 {
 453         DECLARE_COMPLETION_ONSTACK(done);
 454         int retval;
 455
 456         helper_lock();
 457         if (sub_info->path[0] == '\0') {
 458                 retval = 0;
 459                 goto out;
 460         }
 461
 462         if (!khelper_wq || usermodehelper_disabled) {
 463                 retval = -EBUSY;
 464                 goto out;
 465         }
 466
 467         sub_info->complete = &done;
 468         sub_info->wait = wait;
 469
 470         queue_work(khelper_wq, &sub_info->work);
 471         if (wait == UMH_NO_WAIT) /* task has freed sub_info */
 472                 return 0;
 473         wait_for_completion(&done);
 474         retval = sub_info->retval;
 475
 476   out:
 477         call_usermodehelper_freeinfo(sub_info);
 478         helper_unlock();
 479         return retval;
 480 }
 481 EXPORT_SYMBOL(call_usermodehelper_exec);
 482
 483 /**
 484  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 485  * @path: path to usermode executable
 486  * @argv: arg vector for process
 487  * @envp: environment for process
 488  * @filp: set to the write-end of a pipe
 489  *
 490  * This is a simple wrapper which executes a usermode-helper function
 491  * with a pipe as stdin.  It is implemented entirely in terms of
 492  * lower-level call_usermodehelper_* functions.
 493  */
 494 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 495                              struct file **filp)
 496 {
 497         struct subprocess_info *sub_info;
 498         int ret;
 499
 500         sub_info = call_usermodehelper_setup(path, argv, envp);
 501         if (sub_info == NULL)
 502                 return -ENOMEM;
 503
 504         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 505         if (ret < 0)
 506                 goto out;
 507
 508         return call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 509
 510   out:
 511         call_usermodehelper_freeinfo(sub_info);
 512         return ret;
 513 }
 514 EXPORT_SYMBOL(call_usermodehelper_pipe);
 515
 516 void __init usermodehelper_init(void)
 517 {
 518         khelper_wq = create_singlethread_workqueue("khelper");
 519         BUG_ON(!khelper_wq);
 520         register_pm_notifier_callback();
 521 }