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         va_start(args, fmt);
  84         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  85         va_end(args);
  86         if (ret >= MODULE_NAME_LEN)
  87                 return -ENAMETOOLONG;
  88
  89         ret = security_kernel_module_request(module_name);
  90         if (ret)
  91                 return ret;
  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                 atomic_dec(&kmod_concurrent);
 114                 return -ENOMEM;
 115         }
 116
 117         trace_module_request(module_name, wait, _RET_IP_);
 118
 119         ret = call_usermodehelper_fns(modprobe_path, argv, envp,
 120                         wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC,
 121                         NULL, NULL, NULL);
 122
 123         atomic_dec(&kmod_concurrent);
 124         return ret;
 125 }
 126 EXPORT_SYMBOL(__request_module);
 127 #endif /* CONFIG_MODULES */
 128
 129 /*
 130  * This is the task which runs the usermode application
 131  */
 132 static int ____call_usermodehelper(void *data)
 133 {
 134         struct subprocess_info *sub_info = data;
 135         int retval;
 136
 137         spin_lock_irq(&current->sighand->siglock);
 138         flush_signal_handlers(current, 1);
 139         spin_unlock_irq(&current->sighand->siglock);
 140
 141         /* We can run anywhere, unlike our parent keventd(). */
 142         set_cpus_allowed_ptr(current, cpu_all_mask);
 143
 144         /*
 145          * Our parent is keventd, which runs with elevated scheduling priority.
 146          * Avoid propagating that into the userspace child.
 147          */
 148         set_user_nice(current, 0);
 149
 150         if (sub_info->init) {
 151                 retval = sub_info->init(sub_info);
 152                 if (retval)
 153                         goto fail;
 154         }
 155
 156         retval = kernel_execve(sub_info->path, sub_info->argv, sub_info->envp);
 157
 158         /* Exec failed? */
 159 fail:
 160         sub_info->retval = retval;
 161         do_exit(0);
 162 }
 163
 164 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 165 {
 166         if (info->cleanup)
 167                 (*info->cleanup)(info);
 168         kfree(info);
 169 }
 170 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 171
 172 /* Keventd can't block, but this (a child) can. */
 173 static int wait_for_helper(void *data)
 174 {
 175         struct subprocess_info *sub_info = data;
 176         pid_t pid;
 177
 178         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 179         spin_lock_irq(&current->sighand->siglock);
 180         current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
 181         spin_unlock_irq(&current->sighand->siglock);
 182
 183         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 184         if (pid < 0) {
 185                 sub_info->retval = pid;
 186         } else {
 187                 int ret = -ECHILD;
 188                 /*
 189                  * Normally it is bogus to call wait4() from in-kernel because
 190                  * wait4() wants to write the exit code to a userspace address.
 191                  * But wait_for_helper() always runs as keventd, and put_user()
 192                  * to a kernel address works OK for kernel threads, due to their
 193                  * having an mm_segment_t which spans the entire address space.
 194                  *
 195                  * Thus the __user pointer cast is valid here.
 196                  */
 197                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 198
 199                 /*
 200                  * If ret is 0, either ____call_usermodehelper failed and the
 201                  * real error code is already in sub_info->retval or
 202                  * sub_info->retval is 0 anyway, so don't mess with it then.
 203                  */
 204                 if (ret)
 205                         sub_info->retval = ret;
 206         }
 207
 208         complete(sub_info->complete);
 209         return 0;
 210 }
 211
 212 /* This is run by khelper thread  */
 213 static void __call_usermodehelper(struct work_struct *work)
 214 {
 215         struct subprocess_info *sub_info =
 216                 container_of(work, struct subprocess_info, work);
 217         enum umh_wait wait = sub_info->wait;
 218         pid_t pid;
 219
 220         /* CLONE_VFORK: wait until the usermode helper has execve'd
 221          * successfully We need the data structures to stay around
 222          * until that is done.  */
 223         if (wait == UMH_WAIT_PROC)
 224                 pid = kernel_thread(wait_for_helper, sub_info,
 225                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 226         else
 227                 pid = kernel_thread(____call_usermodehelper, sub_info,
 228                                     CLONE_VFORK | SIGCHLD);
 229
 230         switch (wait) {
 231         case UMH_NO_WAIT:
 232                 call_usermodehelper_freeinfo(sub_info);
 233                 break;
 234
 235         case UMH_WAIT_PROC:
 236                 if (pid > 0)
 237                         break;
 238                 /* FALLTHROUGH */
 239         case UMH_WAIT_EXEC:
 240                 if (pid < 0)
 241                         sub_info->retval = pid;
 242                 complete(sub_info->complete);
 243         }
 244 }
 245
 246 #ifdef CONFIG_PM_SLEEP
 247 /*
 248  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 249  * (used for preventing user land processes from being created after the user
 250  * land has been frozen during a system-wide hibernation or suspend operation).
 251  */
 252 static int usermodehelper_disabled;
 253
 254 /* Number of helpers running */
 255 static atomic_t running_helpers = ATOMIC_INIT(0);
 256
 257 /*
 258  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 259  * helpers to finish.
 260  */
 261 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 262
 263 /*
 264  * Time to wait for running_helpers to become zero before the setting of
 265  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 266  */
 267 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 268
 269 /**
 270  * usermodehelper_disable - prevent new helpers from being started
 271  */
 272 int usermodehelper_disable(void)
 273 {
 274         long retval;
 275
 276         usermodehelper_disabled = 1;
 277         smp_mb();
 278         /*
 279          * From now on call_usermodehelper_exec() won't start any new
 280          * helpers, so it is sufficient if running_helpers turns out to
 281          * be zero at one point (it may be increased later, but that
 282          * doesn't matter).
 283          */
 284         retval = wait_event_timeout(running_helpers_waitq,
 285                                         atomic_read(&running_helpers) == 0,
 286                                         RUNNING_HELPERS_TIMEOUT);
 287         if (retval)
 288                 return 0;
 289
 290         usermodehelper_disabled = 0;
 291         return -EAGAIN;
 292 }
 293
 294 /**
 295  * usermodehelper_enable - allow new helpers to be started again
 296  */
 297 void usermodehelper_enable(void)
 298 {
 299         usermodehelper_disabled = 0;
 300 }
 301
 302 static void helper_lock(void)
 303 {
 304         atomic_inc(&running_helpers);
 305         smp_mb__after_atomic_inc();
 306 }
 307
 308 static void helper_unlock(void)
 309 {
 310         if (atomic_dec_and_test(&running_helpers))
 311                 wake_up(&running_helpers_waitq);
 312 }
 313 #else /* CONFIG_PM_SLEEP */
 314 #define usermodehelper_disabled 0
 315
 316 static inline void helper_lock(void) {}
 317 static inline void helper_unlock(void) {}
 318 #endif /* CONFIG_PM_SLEEP */
 319
 320 /**
 321  * call_usermodehelper_setup - prepare to call a usermode helper
 322  * @path: path to usermode executable
 323  * @argv: arg vector for process
 324  * @envp: environment for process
 325  * @gfp_mask: gfp mask for memory allocation
 326  *
 327  * Returns either %NULL on allocation failure, or a subprocess_info
 328  * structure.  This should be passed to call_usermodehelper_exec to
 329  * exec the process and free the structure.
 330  */
 331 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 332                                                   char **envp, gfp_t gfp_mask)
 333 {
 334         struct subprocess_info *sub_info;
 335         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 336         if (!sub_info)
 337                 goto out;
 338
 339         INIT_WORK(&sub_info->work, __call_usermodehelper);
 340         sub_info->path = path;
 341         sub_info->argv = argv;
 342         sub_info->envp = envp;
 343   out:
 344         return sub_info;
 345 }
 346 EXPORT_SYMBOL(call_usermodehelper_setup);
 347
 348 /**
 349  * call_usermodehelper_setfns - set a cleanup/init function
 350  * @info: a subprocess_info returned by call_usermodehelper_setup
 351  * @cleanup: a cleanup function
 352  * @init: an init function
 353  * @data: arbitrary context sensitive data
 354  *
 355  * The init function is used to customize the helper process prior to
 356  * exec.  A non-zero return code causes the process to error out, exit,
 357  * and return the failure to the calling process
 358  *
 359  * The cleanup function is just before ethe subprocess_info is about to
 360  * be freed.  This can be used for freeing the argv and envp.  The
 361  * Function must be runnable in either a process context or the
 362  * context in which call_usermodehelper_exec is called.
 363  */
 364 void call_usermodehelper_setfns(struct subprocess_info *info,
 365                     int (*init)(struct subprocess_info *info),
 366                     void (*cleanup)(struct subprocess_info *info),
 367                     void *data)
 368 {
 369         info->cleanup = cleanup;
 370         info->init = init;
 371         info->data = data;
 372 }
 373 EXPORT_SYMBOL(call_usermodehelper_setfns);
 374
 375 /**
 376  * call_usermodehelper_exec - start a usermode application
 377  * @sub_info: information about the subprocessa
 378  * @wait: wait for the application to finish and return status.
 379  *        when -1 don't wait at all, but you get no useful error back when
 380  *        the program couldn't be exec'ed. This makes it safe to call
 381  *        from interrupt context.
 382  *
 383  * Runs a user-space application.  The application is started
 384  * asynchronously if wait is not set, and runs as a child of keventd.
 385  * (ie. it runs with full root capabilities).
 386  */
 387 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 388                              enum umh_wait wait)
 389 {
 390         DECLARE_COMPLETION_ONSTACK(done);
 391         int retval = 0;
 392
 393         helper_lock();
 394         if (sub_info->path[0] == '\0')
 395                 goto out;
 396
 397         if (!khelper_wq || usermodehelper_disabled) {
 398                 retval = -EBUSY;
 399                 goto out;
 400         }
 401
 402         sub_info->complete = &done;
 403         sub_info->wait = wait;
 404
 405         queue_work(khelper_wq, &sub_info->work);
 406         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 407                 goto unlock;
 408         wait_for_completion(&done);
 409         retval = sub_info->retval;
 410
 411 out:
 412         call_usermodehelper_freeinfo(sub_info);
 413 unlock:
 414         helper_unlock();
 415         return retval;
 416 }
 417 EXPORT_SYMBOL(call_usermodehelper_exec);
 418
 419 void __init usermodehelper_init(void)
 420 {
 421         khelper_wq = create_singlethread_workqueue("khelper");
 422         BUG_ON(!khelper_wq);
 423 }