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/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 <asm/uaccess.h>
  40
  41 extern int max_threads;
  42
  43 static struct workqueue_struct *khelper_wq;
  44
  45 #ifdef CONFIG_MODULES
  46
  47 /*
  48         modprobe_path is set via /proc/sys.
  49 */
  50 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  51
  52 /**
  53  * __request_module - try to load a kernel module
  54  * @wait: wait (or not) for the operation to complete
  55  * @fmt: printf style format string for the name of the module
  56  * @...: arguments as specified in the format string
  57  *
  58  * Load a module using the user mode module loader. The function returns
  59  * zero on success or a negative errno code on failure. Note that a
  60  * successful module load does not mean the module did not then unload
  61  * and exit on an error of its own. Callers must check that the service
  62  * they requested is now available not blindly invoke it.
  63  *
  64  * If module auto-loading support is disabled then this function
  65  * becomes a no-operation.
  66  */
  67 int __request_module(bool wait, const char *fmt, ...)
  68 {
  69         va_list args;
  70         char module_name[MODULE_NAME_LEN];
  71         unsigned int max_modprobes;
  72         int ret;
  73         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  74         static char *envp[] = { "HOME=/",
  75                                 "TERM=linux",
  76                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  77                                 NULL };
  78         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  79 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  80         static int kmod_loop_msg;
  81
  82         va_start(args, fmt);
  83         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  84         va_end(args);
  85         if (ret >= MODULE_NAME_LEN)
  86                 return -ENAMETOOLONG;
  87
  88         /* If modprobe needs a service that is in a module, we get a recursive
  89          * loop.  Limit the number of running kmod threads to max_threads/2 or
  90          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  91          * would be to run the parents of this process, counting how many times
  92          * kmod was invoked.  That would mean accessing the internals of the
  93          * process tables to get the command line, proc_pid_cmdline is static
  94          * and it is not worth changing the proc code just to handle this case.
  95          * KAO.
  96          *
  97          * "trace the ppid" is simple, but will fail if someone's
  98          * parent exits.  I think this is as good as it gets. --RR
  99          */
 100         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 101         atomic_inc(&kmod_concurrent);
 102         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 103                 /* We may be blaming an innocent here, but unlikely */
 104                 if (kmod_loop_msg++ < 5)
 105                         printk(KERN_ERR
 106                                "request_module: runaway loop modprobe %s\n",
 107                                module_name);
 108                 atomic_dec(&kmod_concurrent);
 109                 return -ENOMEM;
 110         }
 111
 112         ret = call_usermodehelper(modprobe_path, argv, envp,
 113                         wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 114         atomic_dec(&kmod_concurrent);
 115         return ret;
 116 }
 117 EXPORT_SYMBOL(__request_module);
 118 #endif /* CONFIG_MODULES */
 119
 120 struct subprocess_info {
 121         struct work_struct work;
 122         struct completion *complete;
 123         struct cred *cred;
 124         char *path;
 125         char **argv;
 126         char **envp;
 127         enum umh_wait wait;
 128         int retval;
 129         struct file *stdin;
 130         void (*cleanup)(char **argv, char **envp);
 131 };
 132
 133 /*
 134  * This is the task which runs the usermode application
 135  */
 136 static int ____call_usermodehelper(void *data)
 137 {
 138         struct subprocess_info *sub_info = data;
 139         int retval;
 140
 141         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 142
 143         /* Unblock all signals */
 144         spin_lock_irq(&current->sighand->siglock);
 145         flush_signal_handlers(current, 1);
 146         sigemptyset(&current->blocked);
 147         recalc_sigpending();
 148         spin_unlock_irq(&current->sighand->siglock);
 149
 150         /* Install the credentials */
 151         commit_creds(sub_info->cred);
 152         sub_info->cred = NULL;
 153
 154         /* Install input pipe when needed */
 155         if (sub_info->stdin) {
 156                 struct files_struct *f = current->files;
 157                 struct fdtable *fdt;
 158                 /* no races because files should be private here */
 159                 sys_close(0);
 160                 fd_install(0, sub_info->stdin);
 161                 spin_lock(&f->file_lock);
 162                 fdt = files_fdtable(f);
 163                 FD_SET(0, fdt->open_fds);
 164                 FD_CLR(0, fdt->close_on_exec);
 165                 spin_unlock(&f->file_lock);
 166
 167                 /* and disallow core files too */
 168                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 169         }
 170
 171         /* We can run anywhere, unlike our parent keventd(). */
 172         set_cpus_allowed_ptr(current, cpu_all_mask);
 173
 174         /*
 175          * Our parent is keventd, which runs with elevated scheduling priority.
 176          * Avoid propagating that into the userspace child.
 177          */
 178         set_user_nice(current, 0);
 179
 180         retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);
 181
 182         /* Exec failed? */
 183         sub_info->retval = retval;
 184         do_exit(0);
 185 }
 186
 187 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 188 {
 189         if (info->cleanup)
 190                 (*info->cleanup)(info->argv, info->envp);
 191         if (info->cred)
 192                 put_cred(info->cred);
 193         kfree(info);
 194 }
 195 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 196
 197 /* Keventd can't block, but this (a child) can. */
 198 static int wait_for_helper(void *data)
 199 {
 200         struct subprocess_info *sub_info = data;
 201         pid_t pid;
 202
 203         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 204          * populate the status, but will return -ECHILD. */
 205         allow_signal(SIGCHLD);
 206
 207         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 208         if (pid < 0) {
 209                 sub_info->retval = pid;
 210         } else {
 211                 int ret;
 212
 213                 /*
 214                  * Normally it is bogus to call wait4() from in-kernel because
 215                  * wait4() wants to write the exit code to a userspace address.
 216                  * But wait_for_helper() always runs as keventd, and put_user()
 217                  * to a kernel address works OK for kernel threads, due to their
 218                  * having an mm_segment_t which spans the entire address space.
 219                  *
 220                  * Thus the __user pointer cast is valid here.
 221                  */
 222                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 223
 224                 /*
 225                  * If ret is 0, either ____call_usermodehelper failed and the
 226                  * real error code is already in sub_info->retval or
 227                  * sub_info->retval is 0 anyway, so don't mess with it then.
 228                  */
 229                 if (ret)
 230                         sub_info->retval = ret;
 231         }
 232
 233         if (sub_info->wait == UMH_NO_WAIT)
 234                 call_usermodehelper_freeinfo(sub_info);
 235         else
 236                 complete(sub_info->complete);
 237         return 0;
 238 }
 239
 240 /* This is run by khelper thread  */
 241 static void __call_usermodehelper(struct work_struct *work)
 242 {
 243         struct subprocess_info *sub_info =
 244                 container_of(work, struct subprocess_info, work);
 245         pid_t pid;
 246         enum umh_wait wait = sub_info->wait;
 247
 248         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 249
 250         /* CLONE_VFORK: wait until the usermode helper has execve'd
 251          * successfully We need the data structures to stay around
 252          * until that is done.  */
 253         if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
 254                 pid = kernel_thread(wait_for_helper, sub_info,
 255                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 256         else
 257                 pid = kernel_thread(____call_usermodehelper, sub_info,
 258                                     CLONE_VFORK | SIGCHLD);
 259
 260         switch (wait) {
 261         case UMH_NO_WAIT:
 262                 break;
 263
 264         case UMH_WAIT_PROC:
 265                 if (pid > 0)
 266                         break;
 267                 sub_info->retval = pid;
 268                 /* FALLTHROUGH */
 269
 270         case UMH_WAIT_EXEC:
 271                 complete(sub_info->complete);
 272         }
 273 }
 274
 275 #ifdef CONFIG_PM_SLEEP
 276 /*
 277  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 278  * (used for preventing user land processes from being created after the user
 279  * land has been frozen during a system-wide hibernation or suspend operation).
 280  */
 281 static int usermodehelper_disabled;
 282
 283 /* Number of helpers running */
 284 static atomic_t running_helpers = ATOMIC_INIT(0);
 285
 286 /*
 287  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 288  * helpers to finish.
 289  */
 290 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 291
 292 /*
 293  * Time to wait for running_helpers to become zero before the setting of
 294  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 295  */
 296 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 297
 298 /**
 299  * usermodehelper_disable - prevent new helpers from being started
 300  */
 301 int usermodehelper_disable(void)
 302 {
 303         long retval;
 304
 305         usermodehelper_disabled = 1;
 306         smp_mb();
 307         /*
 308          * From now on call_usermodehelper_exec() won't start any new
 309          * helpers, so it is sufficient if running_helpers turns out to
 310          * be zero at one point (it may be increased later, but that
 311          * doesn't matter).
 312          */
 313         retval = wait_event_timeout(running_helpers_waitq,
 314                                         atomic_read(&running_helpers) == 0,
 315                                         RUNNING_HELPERS_TIMEOUT);
 316         if (retval)
 317                 return 0;
 318
 319         usermodehelper_disabled = 0;
 320         return -EAGAIN;
 321 }
 322
 323 /**
 324  * usermodehelper_enable - allow new helpers to be started again
 325  */
 326 void usermodehelper_enable(void)
 327 {
 328         usermodehelper_disabled = 0;
 329 }
 330
 331 static void helper_lock(void)
 332 {
 333         atomic_inc(&running_helpers);
 334         smp_mb__after_atomic_inc();
 335 }
 336
 337 static void helper_unlock(void)
 338 {
 339         if (atomic_dec_and_test(&running_helpers))
 340                 wake_up(&running_helpers_waitq);
 341 }
 342 #else /* CONFIG_PM_SLEEP */
 343 #define usermodehelper_disabled 0
 344
 345 static inline void helper_lock(void) {}
 346 static inline void helper_unlock(void) {}
 347 #endif /* CONFIG_PM_SLEEP */
 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  * @gfp_mask: gfp mask for memory allocation
 355  *
 356  * Returns either %NULL on allocation failure, or a subprocess_info
 357  * structure.  This should be passed to call_usermodehelper_exec to
 358  * exec the process and free the structure.
 359  */
 360 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 361                                                   char **envp, gfp_t gfp_mask)
 362 {
 363         struct subprocess_info *sub_info;
 364         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 365         if (!sub_info)
 366                 goto out;
 367
 368         INIT_WORK(&sub_info->work, __call_usermodehelper);
 369         sub_info->path = path;
 370         sub_info->argv = argv;
 371         sub_info->envp = envp;
 372         sub_info->cred = prepare_usermodehelper_creds();
 373         if (!sub_info->cred)
 374                 return NULL;
 375
 376   out:
 377         return sub_info;
 378 }
 379 EXPORT_SYMBOL(call_usermodehelper_setup);
 380
 381 /**
 382  * call_usermodehelper_setkeys - set the session keys for usermode helper
 383  * @info: a subprocess_info returned by call_usermodehelper_setup
 384  * @session_keyring: the session keyring for the process
 385  */
 386 void call_usermodehelper_setkeys(struct subprocess_info *info,
 387                                  struct key *session_keyring)
 388 {
 389 #ifdef CONFIG_KEYS
 390         struct thread_group_cred *tgcred = info->cred->tgcred;
 391         key_put(tgcred->session_keyring);
 392         tgcred->session_keyring = key_get(session_keyring);
 393 #else
 394         BUG();
 395 #endif
 396 }
 397 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 398
 399 /**
 400  * call_usermodehelper_setcleanup - set a cleanup function
 401  * @info: a subprocess_info returned by call_usermodehelper_setup
 402  * @cleanup: a cleanup function
 403  *
 404  * The cleanup function is just befor ethe subprocess_info is about to
 405  * be freed.  This can be used for freeing the argv and envp.  The
 406  * Function must be runnable in either a process context or the
 407  * context in which call_usermodehelper_exec is called.
 408  */
 409 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 410                                     void (*cleanup)(char **argv, char **envp))
 411 {
 412         info->cleanup = cleanup;
 413 }
 414 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 415
 416 /**
 417  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 418  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 419  * @filp: set to the write-end of a pipe
 420  *
 421  * This constructs a pipe, and sets the read end to be the stdin of the
 422  * subprocess, and returns the write-end in *@filp.
 423  */
 424 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 425                                   struct file **filp)
 426 {
 427         struct file *f;
 428
 429         f = create_write_pipe(0);
 430         if (IS_ERR(f))
 431                 return PTR_ERR(f);
 432         *filp = f;
 433
 434         f = create_read_pipe(f, 0);
 435         if (IS_ERR(f)) {
 436                 free_write_pipe(*filp);
 437                 return PTR_ERR(f);
 438         }
 439         sub_info->stdin = f;
 440
 441         return 0;
 442 }
 443 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 444
 445 /**
 446  * call_usermodehelper_exec - start a usermode application
 447  * @sub_info: information about the subprocessa
 448  * @wait: wait for the application to finish and return status.
 449  *        when -1 don't wait at all, but you get no useful error back when
 450  *        the program couldn't be exec'ed. This makes it safe to call
 451  *        from interrupt context.
 452  *
 453  * Runs a user-space application.  The application is started
 454  * asynchronously if wait is not set, and runs as a child of keventd.
 455  * (ie. it runs with full root capabilities).
 456  */
 457 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 458                              enum umh_wait wait)
 459 {
 460         DECLARE_COMPLETION_ONSTACK(done);
 461         int retval = 0;
 462
 463         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 464
 465         helper_lock();
 466         if (sub_info->path[0] == '\0')
 467                 goto out;
 468
 469         if (!khelper_wq || usermodehelper_disabled) {
 470                 retval = -EBUSY;
 471                 goto out;
 472         }
 473
 474         sub_info->complete = &done;
 475         sub_info->wait = wait;
 476
 477         queue_work(khelper_wq, &sub_info->work);
 478         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 479                 goto unlock;
 480         wait_for_completion(&done);
 481         retval = sub_info->retval;
 482
 483 out:
 484         call_usermodehelper_freeinfo(sub_info);
 485 unlock:
 486         helper_unlock();
 487         return retval;
 488 }
 489 EXPORT_SYMBOL(call_usermodehelper_exec);
 490
 491 /**
 492  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 493  * @path: path to usermode executable
 494  * @argv: arg vector for process
 495  * @envp: environment for process
 496  * @filp: set to the write-end of a pipe
 497  *
 498  * This is a simple wrapper which executes a usermode-helper function
 499  * with a pipe as stdin.  It is implemented entirely in terms of
 500  * lower-level call_usermodehelper_* functions.
 501  */
 502 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 503                              struct file **filp)
 504 {
 505         struct subprocess_info *sub_info;
 506         int ret;
 507
 508         sub_info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL);
 509         if (sub_info == NULL)
 510                 return -ENOMEM;
 511
 512         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 513         if (ret < 0)
 514                 goto out;
 515
 516         return call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 517
 518   out:
 519         call_usermodehelper_freeinfo(sub_info);
 520         return ret;
 521 }
 522 EXPORT_SYMBOL(call_usermodehelper_pipe);
 523
 524 void __init usermodehelper_init(void)
 525 {
 526         khelper_wq = create_singlethread_workqueue("khelper");
 527         BUG_ON(!khelper_wq);
 528 }