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 #include <trace/events/module.h>
  41
  42 extern int max_threads;
  43
  44 static struct workqueue_struct *khelper_wq;
  45
  46 #ifdef CONFIG_MODULES
  47
  48 /*
  49         modprobe_path is set via /proc/sys.
  50 */
  51 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  52
  53 /**
  54  * __request_module - try to load a kernel module
  55  * @wait: wait (or not) for the operation to complete
  56  * @fmt: printf style format string for the name of the module
  57  * @...: arguments as specified in the format string
  58  *
  59  * Load a module using the user mode module loader. The function returns
  60  * zero on success or a negative errno code on failure. Note that a
  61  * successful module load does not mean the module did not then unload
  62  * and exit on an error of its own. Callers must check that the service
  63  * they requested is now available not blindly invoke it.
  64  *
  65  * If module auto-loading support is disabled then this function
  66  * becomes a no-operation.
  67  */
  68 int __request_module(bool wait, const char *fmt, ...)
  69 {
  70         va_list args;
  71         char module_name[MODULE_NAME_LEN];
  72         unsigned int max_modprobes;
  73         int ret;
  74         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  75         static char *envp[] = { "HOME=/",
  76                                 "TERM=linux",
  77                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  78                                 NULL };
  79         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  80 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  81         static int kmod_loop_msg;
  82
  83         ret = security_kernel_module_request();
  84         if (ret)
  85                 return ret;
  86
  87         va_start(args, fmt);
  88         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  89         va_end(args);
  90         if (ret >= MODULE_NAME_LEN)
  91                 return -ENAMETOOLONG;
  92
  93         /* If modprobe needs a service that is in a module, we get a recursive
  94          * loop.  Limit the number of running kmod threads to max_threads/2 or
  95          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  96          * would be to run the parents of this process, counting how many times
  97          * kmod was invoked.  That would mean accessing the internals of the
  98          * process tables to get the command line, proc_pid_cmdline is static
  99          * and it is not worth changing the proc code just to handle this case.
 100          * KAO.
 101          *
 102          * "trace the ppid" is simple, but will fail if someone's
 103          * parent exits.  I think this is as good as it gets. --RR
 104          */
 105         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 106         atomic_inc(&kmod_concurrent);
 107         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 108                 /* We may be blaming an innocent here, but unlikely */
 109                 if (kmod_loop_msg < 5) {
 110                         printk(KERN_ERR
 111                                "request_module: runaway loop modprobe %s\n",
 112                                module_name);
 113                         kmod_loop_msg++;
 114                 }
 115                 atomic_dec(&kmod_concurrent);
 116                 return -ENOMEM;
 117         }
 118
 119         trace_module_request(module_name, wait, _RET_IP_);
 120
 121         ret = call_usermodehelper(modprobe_path, argv, envp,
 122                         wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 123         atomic_dec(&kmod_concurrent);
 124         return ret;
 125 }
 126 EXPORT_SYMBOL(__request_module);
 127 #endif /* CONFIG_MODULES */
 128
 129 struct subprocess_info {
 130         struct work_struct work;
 131         struct completion *complete;
 132         struct cred *cred;
 133         char *path;
 134         char **argv;
 135         char **envp;
 136         enum umh_wait wait;
 137         int retval;
 138         struct file *stdin;
 139         void (*cleanup)(char **argv, char **envp);
 140 };
 141
 142 /*
 143  * This is the task which runs the usermode application
 144  */
 145 static int ____call_usermodehelper(void *data)
 146 {
 147         struct subprocess_info *sub_info = data;
 148         int retval;
 149
 150         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 151
 152         /* Unblock all signals */
 153         spin_lock_irq(&current->sighand->siglock);
 154         flush_signal_handlers(current, 1);
 155         sigemptyset(&current->blocked);
 156         recalc_sigpending();
 157         spin_unlock_irq(&current->sighand->siglock);
 158
 159         /* Install the credentials */
 160         commit_creds(sub_info->cred);
 161         sub_info->cred = NULL;
 162
 163         /* Install input pipe when needed */
 164         if (sub_info->stdin) {
 165                 struct files_struct *f = current->files;
 166                 struct fdtable *fdt;
 167                 /* no races because files should be private here */
 168                 sys_close(0);
 169                 fd_install(0, sub_info->stdin);
 170                 spin_lock(&f->file_lock);
 171                 fdt = files_fdtable(f);
 172                 FD_SET(0, fdt->open_fds);
 173                 FD_CLR(0, fdt->close_on_exec);
 174                 spin_unlock(&f->file_lock);
 175
 176                 /* and disallow core files too */
 177                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 178         }
 179
 180         /* We can run anywhere, unlike our parent keventd(). */
 181         set_cpus_allowed_ptr(current, cpu_all_mask);
 182
 183         /*
 184          * Our parent is keventd, which runs with elevated scheduling priority.
 185          * Avoid propagating that into the userspace child.
 186          */
 187         set_user_nice(current, 0);
 188
 189         retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);
 190
 191         /* Exec failed? */
 192         sub_info->retval = retval;
 193         do_exit(0);
 194 }
 195
 196 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 197 {
 198         if (info->cleanup)
 199                 (*info->cleanup)(info->argv, info->envp);
 200         if (info->cred)
 201                 put_cred(info->cred);
 202         kfree(info);
 203 }
 204 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 205
 206 /* Keventd can't block, but this (a child) can. */
 207 static int wait_for_helper(void *data)
 208 {
 209         struct subprocess_info *sub_info = data;
 210         pid_t pid;
 211
 212         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 213          * populate the status, but will return -ECHILD. */
 214         allow_signal(SIGCHLD);
 215
 216         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 217         if (pid < 0) {
 218                 sub_info->retval = pid;
 219         } else {
 220                 int ret;
 221
 222                 /*
 223                  * Normally it is bogus to call wait4() from in-kernel because
 224                  * wait4() wants to write the exit code to a userspace address.
 225                  * But wait_for_helper() always runs as keventd, and put_user()
 226                  * to a kernel address works OK for kernel threads, due to their
 227                  * having an mm_segment_t which spans the entire address space.
 228                  *
 229                  * Thus the __user pointer cast is valid here.
 230                  */
 231                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 232
 233                 /*
 234                  * If ret is 0, either ____call_usermodehelper failed and the
 235                  * real error code is already in sub_info->retval or
 236                  * sub_info->retval is 0 anyway, so don't mess with it then.
 237                  */
 238                 if (ret)
 239                         sub_info->retval = ret;
 240         }
 241
 242         if (sub_info->wait == UMH_NO_WAIT)
 243                 call_usermodehelper_freeinfo(sub_info);
 244         else
 245                 complete(sub_info->complete);
 246         return 0;
 247 }
 248
 249 /* This is run by khelper thread  */
 250 static void __call_usermodehelper(struct work_struct *work)
 251 {
 252         struct subprocess_info *sub_info =
 253                 container_of(work, struct subprocess_info, work);
 254         pid_t pid;
 255         enum umh_wait wait = sub_info->wait;
 256
 257         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 258
 259         /* CLONE_VFORK: wait until the usermode helper has execve'd
 260          * successfully We need the data structures to stay around
 261          * until that is done.  */
 262         if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
 263                 pid = kernel_thread(wait_for_helper, sub_info,
 264                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 265         else
 266                 pid = kernel_thread(____call_usermodehelper, sub_info,
 267                                     CLONE_VFORK | SIGCHLD);
 268
 269         switch (wait) {
 270         case UMH_NO_WAIT:
 271                 break;
 272
 273         case UMH_WAIT_PROC:
 274                 if (pid > 0)
 275                         break;
 276                 sub_info->retval = pid;
 277                 /* FALLTHROUGH */
 278
 279         case UMH_WAIT_EXEC:
 280                 complete(sub_info->complete);
 281         }
 282 }
 283
 284 #ifdef CONFIG_PM_SLEEP
 285 /*
 286  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 287  * (used for preventing user land processes from being created after the user
 288  * land has been frozen during a system-wide hibernation or suspend operation).
 289  */
 290 static int usermodehelper_disabled;
 291
 292 /* Number of helpers running */
 293 static atomic_t running_helpers = ATOMIC_INIT(0);
 294
 295 /*
 296  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 297  * helpers to finish.
 298  */
 299 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 300
 301 /*
 302  * Time to wait for running_helpers to become zero before the setting of
 303  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 304  */
 305 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 306
 307 /**
 308  * usermodehelper_disable - prevent new helpers from being started
 309  */
 310 int usermodehelper_disable(void)
 311 {
 312         long retval;
 313
 314         usermodehelper_disabled = 1;
 315         smp_mb();
 316         /*
 317          * From now on call_usermodehelper_exec() won't start any new
 318          * helpers, so it is sufficient if running_helpers turns out to
 319          * be zero at one point (it may be increased later, but that
 320          * doesn't matter).
 321          */
 322         retval = wait_event_timeout(running_helpers_waitq,
 323                                         atomic_read(&running_helpers) == 0,
 324                                         RUNNING_HELPERS_TIMEOUT);
 325         if (retval)
 326                 return 0;
 327
 328         usermodehelper_disabled = 0;
 329         return -EAGAIN;
 330 }
 331
 332 /**
 333  * usermodehelper_enable - allow new helpers to be started again
 334  */
 335 void usermodehelper_enable(void)
 336 {
 337         usermodehelper_disabled = 0;
 338 }
 339
 340 static void helper_lock(void)
 341 {
 342         atomic_inc(&running_helpers);
 343         smp_mb__after_atomic_inc();
 344 }
 345
 346 static void helper_unlock(void)
 347 {
 348         if (atomic_dec_and_test(&running_helpers))
 349                 wake_up(&running_helpers_waitq);
 350 }
 351 #else /* CONFIG_PM_SLEEP */
 352 #define usermodehelper_disabled 0
 353
 354 static inline void helper_lock(void) {}
 355 static inline void helper_unlock(void) {}
 356 #endif /* CONFIG_PM_SLEEP */
 357
 358 /**
 359  * call_usermodehelper_setup - prepare to call a usermode helper
 360  * @path: path to usermode executable
 361  * @argv: arg vector for process
 362  * @envp: environment for process
 363  * @gfp_mask: gfp mask for memory allocation
 364  *
 365  * Returns either %NULL on allocation failure, or a subprocess_info
 366  * structure.  This should be passed to call_usermodehelper_exec to
 367  * exec the process and free the structure.
 368  */
 369 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 370                                                   char **envp, gfp_t gfp_mask)
 371 {
 372         struct subprocess_info *sub_info;
 373         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 374         if (!sub_info)
 375                 goto out;
 376
 377         INIT_WORK(&sub_info->work, __call_usermodehelper);
 378         sub_info->path = path;
 379         sub_info->argv = argv;
 380         sub_info->envp = envp;
 381         sub_info->cred = prepare_usermodehelper_creds();
 382         if (!sub_info->cred) {
 383                 kfree(sub_info);
 384                 return NULL;
 385         }
 386
 387   out:
 388         return sub_info;
 389 }
 390 EXPORT_SYMBOL(call_usermodehelper_setup);
 391
 392 /**
 393  * call_usermodehelper_setkeys - set the session keys for usermode helper
 394  * @info: a subprocess_info returned by call_usermodehelper_setup
 395  * @session_keyring: the session keyring for the process
 396  */
 397 void call_usermodehelper_setkeys(struct subprocess_info *info,
 398                                  struct key *session_keyring)
 399 {
 400 #ifdef CONFIG_KEYS
 401         struct thread_group_cred *tgcred = info->cred->tgcred;
 402         key_put(tgcred->session_keyring);
 403         tgcred->session_keyring = key_get(session_keyring);
 404 #else
 405         BUG();
 406 #endif
 407 }
 408 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 409
 410 /**
 411  * call_usermodehelper_setcleanup - set a cleanup function
 412  * @info: a subprocess_info returned by call_usermodehelper_setup
 413  * @cleanup: a cleanup function
 414  *
 415  * The cleanup function is just befor ethe subprocess_info is about to
 416  * be freed.  This can be used for freeing the argv and envp.  The
 417  * Function must be runnable in either a process context or the
 418  * context in which call_usermodehelper_exec is called.
 419  */
 420 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 421                                     void (*cleanup)(char **argv, char **envp))
 422 {
 423         info->cleanup = cleanup;
 424 }
 425 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 426
 427 /**
 428  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 429  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 430  * @filp: set to the write-end of a pipe
 431  *
 432  * This constructs a pipe, and sets the read end to be the stdin of the
 433  * subprocess, and returns the write-end in *@filp.
 434  */
 435 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 436                                   struct file **filp)
 437 {
 438         struct file *f;
 439
 440         f = create_write_pipe(0);
 441         if (IS_ERR(f))
 442                 return PTR_ERR(f);
 443         *filp = f;
 444
 445         f = create_read_pipe(f, 0);
 446         if (IS_ERR(f)) {
 447                 free_write_pipe(*filp);
 448                 return PTR_ERR(f);
 449         }
 450         sub_info->stdin = f;
 451
 452         return 0;
 453 }
 454 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 455
 456 /**
 457  * call_usermodehelper_exec - start a usermode application
 458  * @sub_info: information about the subprocessa
 459  * @wait: wait for the application to finish and return status.
 460  *        when -1 don't wait at all, but you get no useful error back when
 461  *        the program couldn't be exec'ed. This makes it safe to call
 462  *        from interrupt context.
 463  *
 464  * Runs a user-space application.  The application is started
 465  * asynchronously if wait is not set, and runs as a child of keventd.
 466  * (ie. it runs with full root capabilities).
 467  */
 468 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 469                              enum umh_wait wait)
 470 {
 471         DECLARE_COMPLETION_ONSTACK(done);
 472         int retval = 0;
 473
 474         BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
 475         validate_creds(sub_info->cred);
 476
 477         helper_lock();
 478         if (sub_info->path[0] == '\0')
 479                 goto out;
 480
 481         if (!khelper_wq || usermodehelper_disabled) {
 482                 retval = -EBUSY;
 483                 goto out;
 484         }
 485
 486         sub_info->complete = &done;
 487         sub_info->wait = wait;
 488
 489         queue_work(khelper_wq, &sub_info->work);
 490         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 491                 goto unlock;
 492         wait_for_completion(&done);
 493         retval = sub_info->retval;
 494
 495 out:
 496         call_usermodehelper_freeinfo(sub_info);
 497 unlock:
 498         helper_unlock();
 499         return retval;
 500 }
 501 EXPORT_SYMBOL(call_usermodehelper_exec);
 502
 503 /**
 504  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 505  * @path: path to usermode executable
 506  * @argv: arg vector for process
 507  * @envp: environment for process
 508  * @filp: set to the write-end of a pipe
 509  *
 510  * This is a simple wrapper which executes a usermode-helper function
 511  * with a pipe as stdin.  It is implemented entirely in terms of
 512  * lower-level call_usermodehelper_* functions.
 513  */
 514 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 515                              struct file **filp)
 516 {
 517         struct subprocess_info *sub_info;
 518         int ret;
 519
 520         sub_info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL);
 521         if (sub_info == NULL)
 522                 return -ENOMEM;
 523
 524         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 525         if (ret < 0)
 526                 goto out;
 527
 528         return call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 529
 530   out:
 531         call_usermodehelper_freeinfo(sub_info);
 532         return ret;
 533 }
 534 EXPORT_SYMBOL(call_usermodehelper_pipe);
 535
 536 void __init usermodehelper_init(void)
 537 {
 538         khelper_wq = create_singlethread_workqueue("khelper");
 539         BUG_ON(!khelper_wq);
 540 }