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/file.h>
  29 #include <linux/fdtable.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_MODULES
  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  * @wait: wait (or not) for the operation to complete
  54  * @fmt: printf style format string for the name of the module
  55  * @...: arguments as specified in the format string
  56  *
  57  * Load a module using the user mode module loader. The function returns
  58  * zero on success or a negative errno code on failure. Note that a
  59  * successful module load does not mean the module did not then unload
  60  * and exit on an error of its own. Callers must check that the service
  61  * they requested is now available not blindly invoke it.
  62  *
  63  * If module auto-loading support is disabled then this function
  64  * becomes a no-operation.
  65  */
  66 int __request_module(bool wait, const char *fmt, ...)
  67 {
  68         va_list args;
  69         char module_name[MODULE_NAME_LEN];
  70         unsigned int max_modprobes;
  71         int ret;
  72         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  73         static char *envp[] = { "HOME=/",
  74                                 "TERM=linux",
  75                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  76                                 NULL };
  77         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  78 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  79         static int kmod_loop_msg;
  80
  81         va_start(args, fmt);
  82         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  83         va_end(args);
  84         if (ret >= MODULE_NAME_LEN)
  85                 return -ENAMETOOLONG;
  86
  87         /* If modprobe needs a service that is in a module, we get a recursive
  88          * loop.  Limit the number of running kmod threads to max_threads/2 or
  89          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  90          * would be to run the parents of this process, counting how many times
  91          * kmod was invoked.  That would mean accessing the internals of the
  92          * process tables to get the command line, proc_pid_cmdline is static
  93          * and it is not worth changing the proc code just to handle this case.
  94          * KAO.
  95          *
  96          * "trace the ppid" is simple, but will fail if someone's
  97          * parent exits.  I think this is as good as it gets. --RR
  98          */
  99         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 100         atomic_inc(&kmod_concurrent);
 101         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 102                 /* We may be blaming an innocent here, but unlikely */
 103                 if (kmod_loop_msg++ < 5)
 104                         printk(KERN_ERR
 105                                "request_module: runaway loop modprobe %s\n",
 106                                module_name);
 107                 atomic_dec(&kmod_concurrent);
 108                 return -ENOMEM;
 109         }
 110
 111         ret = call_usermodehelper(modprobe_path, argv, envp,
 112                         wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 113         atomic_dec(&kmod_concurrent);
 114         return ret;
 115 }
 116 EXPORT_SYMBOL(__request_module);
 117 #endif /* CONFIG_MODULES */
 118
 119 struct subprocess_info {
 120         struct work_struct work;
 121         struct completion *complete;
 122         struct cred *cred;
 123         char *path;
 124         char **argv;
 125         char **envp;
 126         enum umh_wait wait;
 127         int retval;
 128         struct file *stdin;
 129         void (*cleanup)(char **argv, char **envp);
 130 };
 131
 132 /*
 133  * This is the task which runs the usermode application
 134  */
 135 static int ____call_usermodehelper(void *data)
 136 {
 137         struct subprocess_info *sub_info = data;
 138         int retval;
 139
 140         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 141
 142         /* Unblock all signals */
 143         spin_lock_irq(&current->sighand->siglock);
 144         flush_signal_handlers(current, 1);
 145         sigemptyset(&current->blocked);
 146         recalc_sigpending();
 147         spin_unlock_irq(&current->sighand->siglock);
 148
 149         /* Install the credentials */
 150         commit_creds(sub_info->cred);
 151         sub_info->cred = NULL;
 152
 153         /* Install input pipe when needed */
 154         if (sub_info->stdin) {
 155                 struct files_struct *f = current->files;
 156                 struct fdtable *fdt;
 157                 /* no races because files should be private here */
 158                 sys_close(0);
 159                 fd_install(0, sub_info->stdin);
 160                 spin_lock(&f->file_lock);
 161                 fdt = files_fdtable(f);
 162                 FD_SET(0, fdt->open_fds);
 163                 FD_CLR(0, fdt->close_on_exec);
 164                 spin_unlock(&f->file_lock);
 165
 166                 /* and disallow core files too */
 167                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 168         }
 169
 170         /* We can run anywhere, unlike our parent keventd(). */
 171         set_cpus_allowed_ptr(current, cpu_all_mask);
 172
 173         /*
 174          * Our parent is keventd, which runs with elevated scheduling priority.
 175          * Avoid propagating that into the userspace child.
 176          */
 177         set_user_nice(current, 0);
 178
 179         retval = kernel_execve(sub_info->path, 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         if (info->cred)
 191                 put_cred(info->cred);
 192         kfree(info);
 193 }
 194 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 195
 196 /* Keventd can't block, but this (a child) can. */
 197 static int wait_for_helper(void *data)
 198 {
 199         struct subprocess_info *sub_info = data;
 200         pid_t pid;
 201
 202         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 203          * populate the status, but will return -ECHILD. */
 204         allow_signal(SIGCHLD);
 205
 206         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 207         if (pid < 0) {
 208                 sub_info->retval = pid;
 209         } else {
 210                 int ret;
 211
 212                 /*
 213                  * Normally it is bogus to call wait4() from in-kernel because
 214                  * wait4() wants to write the exit code to a userspace address.
 215                  * But wait_for_helper() always runs as keventd, and put_user()
 216                  * to a kernel address works OK for kernel threads, due to their
 217                  * having an mm_segment_t which spans the entire address space.
 218                  *
 219                  * Thus the __user pointer cast is valid here.
 220                  */
 221                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 222
 223                 /*
 224                  * If ret is 0, either ____call_usermodehelper failed and the
 225                  * real error code is already in sub_info->retval or
 226                  * sub_info->retval is 0 anyway, so don't mess with it then.
 227                  */
 228                 if (ret)
 229                         sub_info->retval = ret;
 230         }
 231
 232         if (sub_info->wait == UMH_NO_WAIT)
 233                 call_usermodehelper_freeinfo(sub_info);
 234         else
 235                 complete(sub_info->complete);
 236         return 0;
 237 }
 238
 239 /* This is run by khelper thread  */
 240 static void __call_usermodehelper(struct work_struct *work)
 241 {
 242         struct subprocess_info *sub_info =
 243                 container_of(work, struct subprocess_info, work);
 244         pid_t pid;
 245         enum umh_wait wait = sub_info->wait;
 246
 247         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 248
 249         /* CLONE_VFORK: wait until the usermode helper has execve'd
 250          * successfully We need the data structures to stay around
 251          * until that is done.  */
 252         if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
 253                 pid = kernel_thread(wait_for_helper, sub_info,
 254                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 255         else
 256                 pid = kernel_thread(____call_usermodehelper, sub_info,
 257                                     CLONE_VFORK | SIGCHLD);
 258
 259         switch (wait) {
 260         case UMH_NO_WAIT:
 261                 break;
 262
 263         case UMH_WAIT_PROC:
 264                 if (pid > 0)
 265                         break;
 266                 sub_info->retval = pid;
 267                 /* FALLTHROUGH */
 268
 269         case UMH_WAIT_EXEC:
 270                 complete(sub_info->complete);
 271         }
 272 }
 273
 274 #ifdef CONFIG_PM_SLEEP
 275 /*
 276  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 277  * (used for preventing user land processes from being created after the user
 278  * land has been frozen during a system-wide hibernation or suspend operation).
 279  */
 280 static int usermodehelper_disabled;
 281
 282 /* Number of helpers running */
 283 static atomic_t running_helpers = ATOMIC_INIT(0);
 284
 285 /*
 286  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 287  * helpers to finish.
 288  */
 289 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 290
 291 /*
 292  * Time to wait for running_helpers to become zero before the setting of
 293  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 294  */
 295 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 296
 297 /**
 298  * usermodehelper_disable - prevent new helpers from being started
 299  */
 300 int usermodehelper_disable(void)
 301 {
 302         long retval;
 303
 304         usermodehelper_disabled = 1;
 305         smp_mb();
 306         /*
 307          * From now on call_usermodehelper_exec() won't start any new
 308          * helpers, so it is sufficient if running_helpers turns out to
 309          * be zero at one point (it may be increased later, but that
 310          * doesn't matter).
 311          */
 312         retval = wait_event_timeout(running_helpers_waitq,
 313                                         atomic_read(&running_helpers) == 0,
 314                                         RUNNING_HELPERS_TIMEOUT);
 315         if (retval)
 316                 return 0;
 317
 318         usermodehelper_disabled = 0;
 319         return -EAGAIN;
 320 }
 321
 322 /**
 323  * usermodehelper_enable - allow new helpers to be started again
 324  */
 325 void usermodehelper_enable(void)
 326 {
 327         usermodehelper_disabled = 0;
 328 }
 329
 330 static void helper_lock(void)
 331 {
 332         atomic_inc(&running_helpers);
 333         smp_mb__after_atomic_inc();
 334 }
 335
 336 static void helper_unlock(void)
 337 {
 338         if (atomic_dec_and_test(&running_helpers))
 339                 wake_up(&running_helpers_waitq);
 340 }
 341 #else /* CONFIG_PM_SLEEP */
 342 #define usermodehelper_disabled 0
 343
 344 static inline void helper_lock(void) {}
 345 static inline void helper_unlock(void) {}
 346 #endif /* CONFIG_PM_SLEEP */
 347
 348 /**
 349  * call_usermodehelper_setup - prepare to call a usermode helper
 350  * @path: path to usermode executable
 351  * @argv: arg vector for process
 352  * @envp: environment for process
 353  * @gfp_mask: gfp mask for memory allocation
 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, char **argv,
 360                                                   char **envp, gfp_t gfp_mask)
 361 {
 362         struct subprocess_info *sub_info;
 363         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 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         sub_info->cred = prepare_usermodehelper_creds();
 372         if (!sub_info->cred) {
 373                 kfree(sub_info);
 374                 return NULL;
 375         }
 376
 377   out:
 378         return sub_info;
 379 }
 380 EXPORT_SYMBOL(call_usermodehelper_setup);
 381
 382 /**
 383  * call_usermodehelper_setkeys - set the session keys for usermode helper
 384  * @info: a subprocess_info returned by call_usermodehelper_setup
 385  * @session_keyring: the session keyring for the process
 386  */
 387 void call_usermodehelper_setkeys(struct subprocess_info *info,
 388                                  struct key *session_keyring)
 389 {
 390 #ifdef CONFIG_KEYS
 391         struct thread_group_cred *tgcred = info->cred->tgcred;
 392         key_put(tgcred->session_keyring);
 393         tgcred->session_keyring = key_get(session_keyring);
 394 #else
 395         BUG();
 396 #endif
 397 }
 398 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 399
 400 /**
 401  * call_usermodehelper_setcleanup - set a cleanup function
 402  * @info: a subprocess_info returned by call_usermodehelper_setup
 403  * @cleanup: a cleanup function
 404  *
 405  * The cleanup function is just befor ethe subprocess_info is about to
 406  * be freed.  This can be used for freeing the argv and envp.  The
 407  * Function must be runnable in either a process context or the
 408  * context in which call_usermodehelper_exec is called.
 409  */
 410 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 411                                     void (*cleanup)(char **argv, char **envp))
 412 {
 413         info->cleanup = cleanup;
 414 }
 415 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 416
 417 /**
 418  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 419  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 420  * @filp: set to the write-end of a pipe
 421  *
 422  * This constructs a pipe, and sets the read end to be the stdin of the
 423  * subprocess, and returns the write-end in *@filp.
 424  */
 425 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 426                                   struct file **filp)
 427 {
 428         struct file *f;
 429
 430         f = create_write_pipe(0);
 431         if (IS_ERR(f))
 432                 return PTR_ERR(f);
 433         *filp = f;
 434
 435         f = create_read_pipe(f, 0);
 436         if (IS_ERR(f)) {
 437                 free_write_pipe(*filp);
 438                 return PTR_ERR(f);
 439         }
 440         sub_info->stdin = f;
 441
 442         return 0;
 443 }
 444 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 445
 446 /**
 447  * call_usermodehelper_exec - start a usermode application
 448  * @sub_info: information about the subprocessa
 449  * @wait: wait for the application to finish and return status.
 450  *        when -1 don't wait at all, but you get no useful error back when
 451  *        the program couldn't be exec'ed. This makes it safe to call
 452  *        from interrupt context.
 453  *
 454  * Runs a user-space application.  The application is started
 455  * asynchronously if wait is not set, and runs as a child of keventd.
 456  * (ie. it runs with full root capabilities).
 457  */
 458 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 459                              enum umh_wait wait)
 460 {
 461         DECLARE_COMPLETION_ONSTACK(done);
 462         int retval = 0;
 463
 464         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 465
 466         helper_lock();
 467         if (sub_info->path[0] == '\0')
 468                 goto out;
 469
 470         if (!khelper_wq || usermodehelper_disabled) {
 471                 retval = -EBUSY;
 472                 goto out;
 473         }
 474
 475         sub_info->complete = &done;
 476         sub_info->wait = wait;
 477
 478         queue_work(khelper_wq, &sub_info->work);
 479         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 480                 goto unlock;
 481         wait_for_completion(&done);
 482         retval = sub_info->retval;
 483
 484 out:
 485         call_usermodehelper_freeinfo(sub_info);
 486 unlock:
 487         helper_unlock();
 488         return retval;
 489 }
 490 EXPORT_SYMBOL(call_usermodehelper_exec);
 491
 492 /**
 493  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 494  * @path: path to usermode executable
 495  * @argv: arg vector for process
 496  * @envp: environment for process
 497  * @filp: set to the write-end of a pipe
 498  *
 499  * This is a simple wrapper which executes a usermode-helper function
 500  * with a pipe as stdin.  It is implemented entirely in terms of
 501  * lower-level call_usermodehelper_* functions.
 502  */
 503 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 504                              struct file **filp)
 505 {
 506         struct subprocess_info *sub_info;
 507         int ret;
 508
 509         sub_info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL);
 510         if (sub_info == NULL)
 511                 return -ENOMEM;
 512
 513         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 514         if (ret < 0)
 515                 goto out;
 516
 517         return call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 518
 519   out:
 520         call_usermodehelper_freeinfo(sub_info);
 521         return ret;
 522 }
 523 EXPORT_SYMBOL(call_usermodehelper_pipe);
 524
 525 void __init usermodehelper_init(void)
 526 {
 527         khelper_wq = create_singlethread_workqueue("khelper");
 528         BUG_ON(!khelper_wq);
 529 }