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  * @fmt:     printf style format string for the name of the module
  55  * @varargs: arguements 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(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, 1);
 112         atomic_dec(&kmod_concurrent);
 113         return ret;
 114 }
 115 EXPORT_SYMBOL(request_module);
 116 #endif /* CONFIG_MODULES */
 117
 118 struct subprocess_info {
 119         struct work_struct work;
 120         struct completion *complete;
 121         char *path;
 122         char **argv;
 123         char **envp;
 124         struct key *ring;
 125         enum umh_wait wait;
 126         int retval;
 127         struct file *stdin;
 128         void (*cleanup)(char **argv, char **envp);
 129 };
 130
 131 /*
 132  * This is the task which runs the usermode application
 133  */
 134 static int ____call_usermodehelper(void *data)
 135 {
 136         struct subprocess_info *sub_info = data;
 137         struct key *new_session, *old_session;
 138         int retval;
 139
 140         /* Unblock all signals and set the session keyring. */
 141         new_session = key_get(sub_info->ring);
 142         spin_lock_irq(&current->sighand->siglock);
 143         old_session = __install_session_keyring(current, new_session);
 144         flush_signal_handlers(current, 1);
 145         sigemptyset(&current->blocked);
 146         recalc_sigpending();
 147         spin_unlock_irq(&current->sighand->siglock);
 148
 149         key_put(old_session);
 150
 151         /* Install input pipe when needed */
 152         if (sub_info->stdin) {
 153                 struct files_struct *f = current->files;
 154                 struct fdtable *fdt;
 155                 /* no races because files should be private here */
 156                 sys_close(0);
 157                 fd_install(0, sub_info->stdin);
 158                 spin_lock(&f->file_lock);
 159                 fdt = files_fdtable(f);
 160                 FD_SET(0, fdt->open_fds);
 161                 FD_CLR(0, fdt->close_on_exec);
 162                 spin_unlock(&f->file_lock);
 163
 164                 /* and disallow core files too */
 165                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 166         }
 167
 168         /* We can run anywhere, unlike our parent keventd(). */
 169         set_cpus_allowed_ptr(current, CPU_MASK_ALL_PTR);
 170
 171         /*
 172          * Our parent is keventd, which runs with elevated scheduling priority.
 173          * Avoid propagating that into the userspace child.
 174          */
 175         set_user_nice(current, 0);
 176
 177         retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);
 178
 179         /* Exec failed? */
 180         sub_info->retval = retval;
 181         do_exit(0);
 182 }
 183
 184 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 185 {
 186         if (info->cleanup)
 187                 (*info->cleanup)(info->argv, info->envp);
 188         kfree(info);
 189 }
 190 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 191
 192 /* Keventd can't block, but this (a child) can. */
 193 static int wait_for_helper(void *data)
 194 {
 195         struct subprocess_info *sub_info = data;
 196         pid_t pid;
 197
 198         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 199          * populate the status, but will return -ECHILD. */
 200         allow_signal(SIGCHLD);
 201
 202         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 203         if (pid < 0) {
 204                 sub_info->retval = pid;
 205         } else {
 206                 int ret;
 207
 208                 /*
 209                  * Normally it is bogus to call wait4() from in-kernel because
 210                  * wait4() wants to write the exit code to a userspace address.
 211                  * But wait_for_helper() always runs as keventd, and put_user()
 212                  * to a kernel address works OK for kernel threads, due to their
 213                  * having an mm_segment_t which spans the entire address space.
 214                  *
 215                  * Thus the __user pointer cast is valid here.
 216                  */
 217                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 218
 219                 /*
 220                  * If ret is 0, either ____call_usermodehelper failed and the
 221                  * real error code is already in sub_info->retval or
 222                  * sub_info->retval is 0 anyway, so don't mess with it then.
 223                  */
 224                 if (ret)
 225                         sub_info->retval = ret;
 226         }
 227
 228         if (sub_info->wait == UMH_NO_WAIT)
 229                 call_usermodehelper_freeinfo(sub_info);
 230         else
 231                 complete(sub_info->complete);
 232         return 0;
 233 }
 234
 235 /* This is run by khelper thread  */
 236 static void __call_usermodehelper(struct work_struct *work)
 237 {
 238         struct subprocess_info *sub_info =
 239                 container_of(work, struct subprocess_info, work);
 240         pid_t pid;
 241         enum umh_wait wait = sub_info->wait;
 242
 243         /* CLONE_VFORK: wait until the usermode helper has execve'd
 244          * successfully We need the data structures to stay around
 245          * until that is done.  */
 246         if (wait == UMH_WAIT_PROC || wait == UMH_NO_WAIT)
 247                 pid = kernel_thread(wait_for_helper, sub_info,
 248                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 249         else
 250                 pid = kernel_thread(____call_usermodehelper, sub_info,
 251                                     CLONE_VFORK | SIGCHLD);
 252
 253         switch (wait) {
 254         case UMH_NO_WAIT:
 255                 break;
 256
 257         case UMH_WAIT_PROC:
 258                 if (pid > 0)
 259                         break;
 260                 sub_info->retval = pid;
 261                 /* FALLTHROUGH */
 262
 263         case UMH_WAIT_EXEC:
 264                 complete(sub_info->complete);
 265         }
 266 }
 267
 268 #ifdef CONFIG_PM_SLEEP
 269 /*
 270  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 271  * (used for preventing user land processes from being created after the user
 272  * land has been frozen during a system-wide hibernation or suspend operation).
 273  */
 274 static int usermodehelper_disabled;
 275
 276 /* Number of helpers running */
 277 static atomic_t running_helpers = ATOMIC_INIT(0);
 278
 279 /*
 280  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 281  * helpers to finish.
 282  */
 283 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 284
 285 /*
 286  * Time to wait for running_helpers to become zero before the setting of
 287  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 288  */
 289 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 290
 291 /**
 292  * usermodehelper_disable - prevent new helpers from being started
 293  */
 294 int usermodehelper_disable(void)
 295 {
 296         long retval;
 297
 298         usermodehelper_disabled = 1;
 299         smp_mb();
 300         /*
 301          * From now on call_usermodehelper_exec() won't start any new
 302          * helpers, so it is sufficient if running_helpers turns out to
 303          * be zero at one point (it may be increased later, but that
 304          * doesn't matter).
 305          */
 306         retval = wait_event_timeout(running_helpers_waitq,
 307                                         atomic_read(&running_helpers) == 0,
 308                                         RUNNING_HELPERS_TIMEOUT);
 309         if (retval)
 310                 return 0;
 311
 312         usermodehelper_disabled = 0;
 313         return -EAGAIN;
 314 }
 315
 316 /**
 317  * usermodehelper_enable - allow new helpers to be started again
 318  */
 319 void usermodehelper_enable(void)
 320 {
 321         usermodehelper_disabled = 0;
 322 }
 323
 324 static void helper_lock(void)
 325 {
 326         atomic_inc(&running_helpers);
 327         smp_mb__after_atomic_inc();
 328 }
 329
 330 static void helper_unlock(void)
 331 {
 332         if (atomic_dec_and_test(&running_helpers))
 333                 wake_up(&running_helpers_waitq);
 334 }
 335 #else /* CONFIG_PM_SLEEP */
 336 #define usermodehelper_disabled 0
 337
 338 static inline void helper_lock(void) {}
 339 static inline void helper_unlock(void) {}
 340 #endif /* CONFIG_PM_SLEEP */
 341
 342 /**
 343  * call_usermodehelper_setup - prepare to call a usermode helper
 344  * @path: path to usermode executable
 345  * @argv: arg vector for process
 346  * @envp: environment for process
 347  * @gfp_mask: gfp mask for memory allocation
 348  *
 349  * Returns either %NULL on allocation failure, or a subprocess_info
 350  * structure.  This should be passed to call_usermodehelper_exec to
 351  * exec the process and free the structure.
 352  */
 353 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 354                                                   char **envp, gfp_t gfp_mask)
 355 {
 356         struct subprocess_info *sub_info;
 357         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 358         if (!sub_info)
 359                 goto out;
 360
 361         INIT_WORK(&sub_info->work, __call_usermodehelper);
 362         sub_info->path = path;
 363         sub_info->argv = argv;
 364         sub_info->envp = envp;
 365
 366   out:
 367         return sub_info;
 368 }
 369 EXPORT_SYMBOL(call_usermodehelper_setup);
 370
 371 /**
 372  * call_usermodehelper_setkeys - set the session keys for usermode helper
 373  * @info: a subprocess_info returned by call_usermodehelper_setup
 374  * @session_keyring: the session keyring for the process
 375  */
 376 void call_usermodehelper_setkeys(struct subprocess_info *info,
 377                                  struct key *session_keyring)
 378 {
 379         info->ring = session_keyring;
 380 }
 381 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 382
 383 /**
 384  * call_usermodehelper_setcleanup - set a cleanup function
 385  * @info: a subprocess_info returned by call_usermodehelper_setup
 386  * @cleanup: a cleanup function
 387  *
 388  * The cleanup function is just befor ethe subprocess_info is about to
 389  * be freed.  This can be used for freeing the argv and envp.  The
 390  * Function must be runnable in either a process context or the
 391  * context in which call_usermodehelper_exec is called.
 392  */
 393 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 394                                     void (*cleanup)(char **argv, char **envp))
 395 {
 396         info->cleanup = cleanup;
 397 }
 398 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 399
 400 /**
 401  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 402  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 403  * @filp: set to the write-end of a pipe
 404  *
 405  * This constructs a pipe, and sets the read end to be the stdin of the
 406  * subprocess, and returns the write-end in *@filp.
 407  */
 408 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 409                                   struct file **filp)
 410 {
 411         struct file *f;
 412
 413         f = create_write_pipe(0);
 414         if (IS_ERR(f))
 415                 return PTR_ERR(f);
 416         *filp = f;
 417
 418         f = create_read_pipe(f, 0);
 419         if (IS_ERR(f)) {
 420                 free_write_pipe(*filp);
 421                 return PTR_ERR(f);
 422         }
 423         sub_info->stdin = f;
 424
 425         return 0;
 426 }
 427 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 428
 429 /**
 430  * call_usermodehelper_exec - start a usermode application
 431  * @sub_info: information about the subprocessa
 432  * @wait: wait for the application to finish and return status.
 433  *        when -1 don't wait at all, but you get no useful error back when
 434  *        the program couldn't be exec'ed. This makes it safe to call
 435  *        from interrupt context.
 436  *
 437  * Runs a user-space application.  The application is started
 438  * asynchronously if wait is not set, and runs as a child of keventd.
 439  * (ie. it runs with full root capabilities).
 440  */
 441 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 442                              enum umh_wait wait)
 443 {
 444         DECLARE_COMPLETION_ONSTACK(done);
 445         int retval = 0;
 446
 447         helper_lock();
 448         if (sub_info->path[0] == '\0')
 449                 goto out;
 450
 451         if (!khelper_wq || usermodehelper_disabled) {
 452                 retval = -EBUSY;
 453                 goto out;
 454         }
 455
 456         sub_info->complete = &done;
 457         sub_info->wait = wait;
 458
 459         queue_work(khelper_wq, &sub_info->work);
 460         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 461                 goto unlock;
 462         wait_for_completion(&done);
 463         retval = sub_info->retval;
 464
 465 out:
 466         call_usermodehelper_freeinfo(sub_info);
 467 unlock:
 468         helper_unlock();
 469         return retval;
 470 }
 471 EXPORT_SYMBOL(call_usermodehelper_exec);
 472
 473 /**
 474  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 475  * @path: path to usermode executable
 476  * @argv: arg vector for process
 477  * @envp: environment for process
 478  * @filp: set to the write-end of a pipe
 479  *
 480  * This is a simple wrapper which executes a usermode-helper function
 481  * with a pipe as stdin.  It is implemented entirely in terms of
 482  * lower-level call_usermodehelper_* functions.
 483  */
 484 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 485                              struct file **filp)
 486 {
 487         struct subprocess_info *sub_info;
 488         int ret;
 489
 490         sub_info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL);
 491         if (sub_info == NULL)
 492                 return -ENOMEM;
 493
 494         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 495         if (ret < 0)
 496                 goto out;
 497
 498         return call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 499
 500   out:
 501         call_usermodehelper_freeinfo(sub_info);
 502         return ret;
 503 }
 504 EXPORT_SYMBOL(call_usermodehelper_pipe);
 505
 506 void __init usermodehelper_init(void)
 507 {
 508         khelper_wq = create_singlethread_workqueue("khelper");
 509         BUG_ON(!khelper_wq);
 510 }