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,
 157                                (const char *const *)sub_info->argv,
 158                                (const char *const *)sub_info->envp);
 159
 160         /* Exec failed? */
 161 fail:
 162         sub_info->retval = retval;
 163         do_exit(0);
 164 }
 165
 166 void call_usermodehelper_freeinfo(struct subprocess_info *info)
 167 {
 168         if (info->cleanup)
 169                 (*info->cleanup)(info);
 170         kfree(info);
 171 }
 172 EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 173
 174 /* Keventd can't block, but this (a child) can. */
 175 static int wait_for_helper(void *data)
 176 {
 177         struct subprocess_info *sub_info = data;
 178         pid_t pid;
 179
 180         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 181         spin_lock_irq(&current->sighand->siglock);
 182         current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
 183         spin_unlock_irq(&current->sighand->siglock);
 184
 185         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 186         if (pid < 0) {
 187                 sub_info->retval = pid;
 188         } else {
 189                 int ret = -ECHILD;
 190                 /*
 191                  * Normally it is bogus to call wait4() from in-kernel because
 192                  * wait4() wants to write the exit code to a userspace address.
 193                  * But wait_for_helper() always runs as keventd, and put_user()
 194                  * to a kernel address works OK for kernel threads, due to their
 195                  * having an mm_segment_t which spans the entire address space.
 196                  *
 197                  * Thus the __user pointer cast is valid here.
 198                  */
 199                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 200
 201                 /*
 202                  * If ret is 0, either ____call_usermodehelper failed and the
 203                  * real error code is already in sub_info->retval or
 204                  * sub_info->retval is 0 anyway, so don't mess with it then.
 205                  */
 206                 if (ret)
 207                         sub_info->retval = ret;
 208         }
 209
 210         complete(sub_info->complete);
 211         return 0;
 212 }
 213
 214 /* This is run by khelper thread  */
 215 static void __call_usermodehelper(struct work_struct *work)
 216 {
 217         struct subprocess_info *sub_info =
 218                 container_of(work, struct subprocess_info, work);
 219         enum umh_wait wait = sub_info->wait;
 220         pid_t pid;
 221
 222         /* CLONE_VFORK: wait until the usermode helper has execve'd
 223          * successfully We need the data structures to stay around
 224          * until that is done.  */
 225         if (wait == UMH_WAIT_PROC)
 226                 pid = kernel_thread(wait_for_helper, sub_info,
 227                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 228         else
 229                 pid = kernel_thread(____call_usermodehelper, sub_info,
 230                                     CLONE_VFORK | SIGCHLD);
 231
 232         switch (wait) {
 233         case UMH_NO_WAIT:
 234                 call_usermodehelper_freeinfo(sub_info);
 235                 break;
 236
 237         case UMH_WAIT_PROC:
 238                 if (pid > 0)
 239                         break;
 240                 /* FALLTHROUGH */
 241         case UMH_WAIT_EXEC:
 242                 if (pid < 0)
 243                         sub_info->retval = pid;
 244                 complete(sub_info->complete);
 245         }
 246 }
 247
 248 /*
 249  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 250  * (used for preventing user land processes from being created after the user
 251  * land has been frozen during a system-wide hibernation or suspend operation).
 252  */
 253 static int usermodehelper_disabled;
 254
 255 /* Number of helpers running */
 256 static atomic_t running_helpers = ATOMIC_INIT(0);
 257
 258 /*
 259  * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 260  * helpers to finish.
 261  */
 262 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 263
 264 /*
 265  * Time to wait for running_helpers to become zero before the setting of
 266  * usermodehelper_disabled in usermodehelper_pm_callback() fails
 267  */
 268 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 269
 270 /**
 271  * usermodehelper_disable - prevent new helpers from being started
 272  */
 273 int usermodehelper_disable(void)
 274 {
 275         long retval;
 276
 277         usermodehelper_disabled = 1;
 278         smp_mb();
 279         /*
 280          * From now on call_usermodehelper_exec() won't start any new
 281          * helpers, so it is sufficient if running_helpers turns out to
 282          * be zero at one point (it may be increased later, but that
 283          * doesn't matter).
 284          */
 285         retval = wait_event_timeout(running_helpers_waitq,
 286                                         atomic_read(&running_helpers) == 0,
 287                                         RUNNING_HELPERS_TIMEOUT);
 288         if (retval)
 289                 return 0;
 290
 291         usermodehelper_disabled = 0;
 292         return -EAGAIN;
 293 }
 294
 295 /**
 296  * usermodehelper_enable - allow new helpers to be started again
 297  */
 298 void usermodehelper_enable(void)
 299 {
 300         usermodehelper_disabled = 0;
 301 }
 302
 303 /**
 304  * usermodehelper_is_disabled - check if new helpers are allowed to be started
 305  */
 306 bool usermodehelper_is_disabled(void)
 307 {
 308         return usermodehelper_disabled;
 309 }
 310 EXPORT_SYMBOL_GPL(usermodehelper_is_disabled);
 311
 312 static void helper_lock(void)
 313 {
 314         atomic_inc(&running_helpers);
 315         smp_mb__after_atomic_inc();
 316 }
 317
 318 static void helper_unlock(void)
 319 {
 320         if (atomic_dec_and_test(&running_helpers))
 321                 wake_up(&running_helpers_waitq);
 322 }
 323
 324 /**
 325  * call_usermodehelper_setup - prepare to call a usermode helper
 326  * @path: path to usermode executable
 327  * @argv: arg vector for process
 328  * @envp: environment for process
 329  * @gfp_mask: gfp mask for memory allocation
 330  *
 331  * Returns either %NULL on allocation failure, or a subprocess_info
 332  * structure.  This should be passed to call_usermodehelper_exec to
 333  * exec the process and free the structure.
 334  */
 335 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 336                                                   char **envp, gfp_t gfp_mask)
 337 {
 338         struct subprocess_info *sub_info;
 339         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 340         if (!sub_info)
 341                 goto out;
 342
 343         INIT_WORK(&sub_info->work, __call_usermodehelper);
 344         sub_info->path = path;
 345         sub_info->argv = argv;
 346         sub_info->envp = envp;
 347   out:
 348         return sub_info;
 349 }
 350 EXPORT_SYMBOL(call_usermodehelper_setup);
 351
 352 /**
 353  * call_usermodehelper_setfns - set a cleanup/init function
 354  * @info: a subprocess_info returned by call_usermodehelper_setup
 355  * @cleanup: a cleanup function
 356  * @init: an init function
 357  * @data: arbitrary context sensitive data
 358  *
 359  * The init function is used to customize the helper process prior to
 360  * exec.  A non-zero return code causes the process to error out, exit,
 361  * and return the failure to the calling process
 362  *
 363  * The cleanup function is just before ethe subprocess_info is about to
 364  * be freed.  This can be used for freeing the argv and envp.  The
 365  * Function must be runnable in either a process context or the
 366  * context in which call_usermodehelper_exec is called.
 367  */
 368 void call_usermodehelper_setfns(struct subprocess_info *info,
 369                     int (*init)(struct subprocess_info *info),
 370                     void (*cleanup)(struct subprocess_info *info),
 371                     void *data)
 372 {
 373         info->cleanup = cleanup;
 374         info->init = init;
 375         info->data = data;
 376 }
 377 EXPORT_SYMBOL(call_usermodehelper_setfns);
 378
 379 /**
 380  * call_usermodehelper_exec - start a usermode application
 381  * @sub_info: information about the subprocessa
 382  * @wait: wait for the application to finish and return status.
 383  *        when -1 don't wait at all, but you get no useful error back when
 384  *        the program couldn't be exec'ed. This makes it safe to call
 385  *        from interrupt context.
 386  *
 387  * Runs a user-space application.  The application is started
 388  * asynchronously if wait is not set, and runs as a child of keventd.
 389  * (ie. it runs with full root capabilities).
 390  */
 391 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 392                              enum umh_wait wait)
 393 {
 394         DECLARE_COMPLETION_ONSTACK(done);
 395         int retval = 0;
 396
 397         helper_lock();
 398         if (sub_info->path[0] == '\0')
 399                 goto out;
 400
 401         if (!khelper_wq || usermodehelper_disabled) {
 402                 retval = -EBUSY;
 403                 goto out;
 404         }
 405
 406         sub_info->complete = &done;
 407         sub_info->wait = wait;
 408
 409         queue_work(khelper_wq, &sub_info->work);
 410         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 411                 goto unlock;
 412         wait_for_completion(&done);
 413         retval = sub_info->retval;
 414
 415 out:
 416         call_usermodehelper_freeinfo(sub_info);
 417 unlock:
 418         helper_unlock();
 419         return retval;
 420 }
 421 EXPORT_SYMBOL(call_usermodehelper_exec);
 422
 423 void __init usermodehelper_init(void)
 424 {
 425         khelper_wq = create_singlethread_workqueue("khelper");
 426         BUG_ON(!khelper_wq);
 427 }