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/smp_lock.h>
  27 #include <linux/slab.h>
  28 #include <linux/mnt_namespace.h>
  29 #include <linux/completion.h>
  30 #include <linux/file.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 <asm/uaccess.h>
  38
  39 extern int delete_module(const char *name, unsigned int flags);
  40
  41 extern int max_threads;
  42
  43 static struct workqueue_struct *khelper_wq;
  44
  45 #ifdef CONFIG_KMOD
  46
  47 /*
  48         modprobe_path is set via /proc/sys.
  49 */
  50 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  51 struct module_kobject kmod_mk;
  52
  53 /**
  54  * request_module - try to load a kernel module
  55  * @fmt:     printf style format string for the name of the module
  56  * @varargs: arguements as specified in the format string
  57  *
  58  * Load a module using the user mode module loader. The function returns
  59  * zero on success or a negative errno code on failure. Note that a
  60  * successful module load does not mean the module did not then unload
  61  * and exit on an error of its own. Callers must check that the service
  62  * they requested is now available not blindly invoke it.
  63  *
  64  * If module auto-loading support is disabled then this function
  65  * becomes a no-operation.
  66  */
  67 int request_module(const char *fmt, ...)
  68 {
  69         va_list args;
  70         char module_name[MODULE_NAME_LEN];
  71         unsigned int max_modprobes;
  72         int ret;
  73         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  74         static char *envp[] = { "HOME=/",
  75                                 "TERM=linux",
  76                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  77                                 NULL };
  78         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  79 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  80         static int kmod_loop_msg;
  81         char modalias[16 + MODULE_NAME_LEN] = "MODALIAS=";
  82         char *uevent_envp[2] = {
  83                 modalias,
  84                 NULL
  85         };
  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         strcpy(&modalias[strlen("MODALIAS=")], module_name);
  94         kobject_uevent_env(&kmod_mk.kobj, KOBJ_CHANGE, uevent_envp);
  95
  96         if (modprobe_path[0] == '\0')
  97                 goto out;
  98
  99         /* If modprobe needs a service that is in a module, we get a recursive
 100          * loop.  Limit the number of running kmod threads to max_threads/2 or
 101          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 102          * would be to run the parents of this process, counting how many times
 103          * kmod was invoked.  That would mean accessing the internals of the
 104          * process tables to get the command line, proc_pid_cmdline is static
 105          * and it is not worth changing the proc code just to handle this case.
 106          * KAO.
 107          *
 108          * "trace the ppid" is simple, but will fail if someone's
 109          * parent exits.  I think this is as good as it gets. --RR
 110          */
 111         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 112         atomic_inc(&kmod_concurrent);
 113         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 114                 /* We may be blaming an innocent here, but unlikely */
 115                 if (kmod_loop_msg++ < 5)
 116                         printk(KERN_ERR
 117                                "request_module: runaway loop modprobe %s\n",
 118                                module_name);
 119                 atomic_dec(&kmod_concurrent);
 120                 return -ENOMEM;
 121         }
 122
 123         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 124         atomic_dec(&kmod_concurrent);
 125 out:
 126         return ret;
 127 }
 128 EXPORT_SYMBOL(request_module);
 129
 130 static ssize_t store_mod_request(struct module_attribute *mattr,
 131                                  struct module *mod,
 132                               const char *buffer, size_t count)
 133 {
 134         char name[MODULE_NAME_LEN];
 135         int ret;
 136
 137         if (count < 1 || count+1 > MODULE_NAME_LEN)
 138                 return -EINVAL;
 139         memcpy(name, buffer, count);
 140         name[count] = '\0';
 141         if (name[count-1] == '\n')
 142                 name[count-1] = '\0';
 143
 144         ret = request_module(name);
 145         if (ret < 0)
 146                 return ret;
 147         return count;
 148 }
 149
 150 static struct module_attribute mod_request = {
 151         .attr = { .name = "mod_request", .mode = S_IWUSR, .owner = THIS_MODULE },
 152         .store = store_mod_request,
 153 };
 154
 155 #ifdef CONFIG_MODULE_UNLOAD
 156 static ssize_t store_mod_unload(struct module_attribute *mattr,
 157                             struct module *mod,
 158                             const char *buffer, size_t count)
 159 {
 160         char name[MODULE_NAME_LEN];
 161         int ret;
 162
 163         if (count < 1 || count+1 > MODULE_NAME_LEN)
 164                 return -EINVAL;
 165         memcpy(name, buffer, count);
 166         name[count] = '\0';
 167         if (name[count-1] == '\n')
 168                 name[count-1] = '\0';
 169
 170         ret = delete_module(name, O_NONBLOCK);
 171         if (ret < 0)
 172                 return ret;
 173         return count;
 174 }
 175
 176 static struct module_attribute mod_unload = {
 177         .attr = { .name = "mod_unload", .mode = S_IWUSR, .owner = THIS_MODULE },
 178         .store = store_mod_unload,
 179 };
 180 #endif
 181
 182 static ssize_t show_mod_request_helper(struct module_attribute *mattr,
 183                                        struct module *mod,
 184                                        char *buffer)
 185 {
 186         return sprintf(buffer, "%s\n", modprobe_path);
 187 }
 188
 189 static ssize_t store_mod_request_helper(struct module_attribute *mattr,
 190                                         struct module *mod,
 191                                         const char *buffer, size_t count)
 192 {
 193         if (count < 1 || count+1 > KMOD_PATH_LEN)
 194                 return -EINVAL;
 195         memcpy(modprobe_path, buffer, count);
 196         modprobe_path[count] = '\0';
 197         if (modprobe_path[count-1] == '\n')
 198                 modprobe_path[count-1] = '\0';
 199         return count;
 200 }
 201
 202 static struct module_attribute mod_request_helper = {
 203         .attr = {
 204                 .name = "mod_request_helper",
 205                 .mode = S_IWUSR | S_IRUGO,
 206                 .owner = THIS_MODULE
 207         },
 208         .show = show_mod_request_helper,
 209         .store = store_mod_request_helper,
 210 };
 211
 212 void __init kmod_sysfs_init(void)
 213 {
 214         int ret;
 215
 216         kmod_mk.mod = THIS_MODULE;
 217         kobj_set_kset_s(&kmod_mk, module_subsys);
 218         kobject_set_name(&kmod_mk.kobj, "kmod");
 219         kobject_init(&kmod_mk.kobj);
 220         ret = kobject_add(&kmod_mk.kobj);
 221         if (ret < 0)
 222                 goto out;
 223
 224         ret = sysfs_create_file(&kmod_mk.kobj, &mod_request_helper.attr);
 225         ret = sysfs_create_file(&kmod_mk.kobj, &mod_request.attr);
 226 #ifdef CONFIG_MODULE_UNLOAD
 227         ret = sysfs_create_file(&kmod_mk.kobj, &mod_unload.attr);
 228 #endif
 229
 230         kobject_uevent(&kmod_mk.kobj, KOBJ_ADD);
 231 out:
 232         return;
 233 }
 234 #endif /* CONFIG_KMOD */
 235
 236 struct subprocess_info {
 237         struct work_struct work;
 238         struct completion *complete;
 239         char *path;
 240         char **argv;
 241         char **envp;
 242         struct key *ring;
 243         int wait;
 244         int retval;
 245         struct file *stdin;
 246 };
 247
 248 /*
 249  * This is the task which runs the usermode application
 250  */
 251 static int ____call_usermodehelper(void *data)
 252 {
 253         struct subprocess_info *sub_info = data;
 254         struct key *new_session, *old_session;
 255         int retval;
 256
 257         /* Unblock all signals and set the session keyring. */
 258         new_session = key_get(sub_info->ring);
 259         flush_signals(current);
 260         spin_lock_irq(&current->sighand->siglock);
 261         old_session = __install_session_keyring(current, new_session);
 262         flush_signal_handlers(current, 1);
 263         sigemptyset(&current->blocked);
 264         recalc_sigpending();
 265         spin_unlock_irq(&current->sighand->siglock);
 266
 267         key_put(old_session);
 268
 269         /* Install input pipe when needed */
 270         if (sub_info->stdin) {
 271                 struct files_struct *f = current->files;
 272                 struct fdtable *fdt;
 273                 /* no races because files should be private here */
 274                 sys_close(0);
 275                 fd_install(0, sub_info->stdin);
 276                 spin_lock(&f->file_lock);
 277                 fdt = files_fdtable(f);
 278                 FD_SET(0, fdt->open_fds);
 279                 FD_CLR(0, fdt->close_on_exec);
 280                 spin_unlock(&f->file_lock);
 281
 282                 /* and disallow core files too */
 283                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 284         }
 285
 286         /* We can run anywhere, unlike our parent keventd(). */
 287         set_cpus_allowed(current, CPU_MASK_ALL);
 288
 289         retval = -EPERM;
 290         if (current->fs->root)
 291                 retval = kernel_execve(sub_info->path,
 292                                 sub_info->argv, sub_info->envp);
 293
 294         /* Exec failed? */
 295         sub_info->retval = retval;
 296         do_exit(0);
 297 }
 298
 299 /* Keventd can't block, but this (a child) can. */
 300 static int wait_for_helper(void *data)
 301 {
 302         struct subprocess_info *sub_info = data;
 303         pid_t pid;
 304         struct k_sigaction sa;
 305
 306         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 307          * populate the status, but will return -ECHILD. */
 308         sa.sa.sa_handler = SIG_IGN;
 309         sa.sa.sa_flags = 0;
 310         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 311         do_sigaction(SIGCHLD, &sa, NULL);
 312         allow_signal(SIGCHLD);
 313
 314         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 315         if (pid < 0) {
 316                 sub_info->retval = pid;
 317         } else {
 318                 int ret;
 319
 320                 /*
 321                  * Normally it is bogus to call wait4() from in-kernel because
 322                  * wait4() wants to write the exit code to a userspace address.
 323                  * But wait_for_helper() always runs as keventd, and put_user()
 324                  * to a kernel address works OK for kernel threads, due to their
 325                  * having an mm_segment_t which spans the entire address space.
 326                  *
 327                  * Thus the __user pointer cast is valid here.
 328                  */
 329                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 330
 331                 /*
 332                  * If ret is 0, either ____call_usermodehelper failed and the
 333                  * real error code is already in sub_info->retval or
 334                  * sub_info->retval is 0 anyway, so don't mess with it then.
 335                  */
 336                 if (ret)
 337                         sub_info->retval = ret;
 338         }
 339
 340         if (sub_info->wait < 0)
 341                 kfree(sub_info);
 342         else
 343                 complete(sub_info->complete);
 344         return 0;
 345 }
 346
 347 /* This is run by khelper thread  */
 348 static void __call_usermodehelper(struct work_struct *work)
 349 {
 350         struct subprocess_info *sub_info =
 351                 container_of(work, struct subprocess_info, work);
 352         pid_t pid;
 353         int wait = sub_info->wait;
 354
 355         /* CLONE_VFORK: wait until the usermode helper has execve'd
 356          * successfully We need the data structures to stay around
 357          * until that is done.  */
 358         if (wait)
 359                 pid = kernel_thread(wait_for_helper, sub_info,
 360                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 361         else
 362                 pid = kernel_thread(____call_usermodehelper, sub_info,
 363                                     CLONE_VFORK | SIGCHLD);
 364
 365         if (wait < 0)
 366                 return;
 367
 368         if (pid < 0) {
 369                 sub_info->retval = pid;
 370                 complete(sub_info->complete);
 371         } else if (!wait)
 372                 complete(sub_info->complete);
 373 }
 374
 375 /**
 376  * call_usermodehelper_keys - start a usermode application
 377  * @path: pathname for the application
 378  * @argv: null-terminated argument list
 379  * @envp: null-terminated environment list
 380  * @session_keyring: session keyring for process (NULL for an empty keyring)
 381  * @wait: wait for the application to finish and return status.
 382  *        when -1 don't wait at all, but you get no useful error back when
 383  *        the program couldn't be exec'ed. This makes it safe to call
 384  *        from interrupt context.
 385  *
 386  * Runs a user-space application.  The application is started
 387  * asynchronously if wait is not set, and runs as a child of keventd.
 388  * (ie. it runs with full root capabilities).
 389  *
 390  * Must be called from process context.  Returns a negative error code
 391  * if program was not execed successfully, or 0.
 392  */
 393 int call_usermodehelper_keys(char *path, char **argv, char **envp,
 394                              struct key *session_keyring, int wait)
 395 {
 396         DECLARE_COMPLETION_ONSTACK(done);
 397         struct subprocess_info *sub_info;
 398         int retval;
 399
 400         if (!khelper_wq)
 401                 return -EBUSY;
 402
 403         if (path[0] == '\0')
 404                 return 0;
 405
 406         sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
 407         if (!sub_info)
 408                 return -ENOMEM;
 409
 410         INIT_WORK(&sub_info->work, __call_usermodehelper);
 411         sub_info->complete = &done;
 412         sub_info->path = path;
 413         sub_info->argv = argv;
 414         sub_info->envp = envp;
 415         sub_info->ring = session_keyring;
 416         sub_info->wait = wait;
 417
 418         queue_work(khelper_wq, &sub_info->work);
 419         if (wait < 0) /* task has freed sub_info */
 420                 return 0;
 421         wait_for_completion(&done);
 422         retval = sub_info->retval;
 423         kfree(sub_info);
 424         return retval;
 425 }
 426 EXPORT_SYMBOL(call_usermodehelper_keys);
 427
 428 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 429                              struct file **filp)
 430 {
 431         DECLARE_COMPLETION(done);
 432         struct subprocess_info sub_info = {
 433                 .work           = __WORK_INITIALIZER(sub_info.work,
 434                                                      __call_usermodehelper),
 435                 .complete       = &done,
 436                 .path           = path,
 437                 .argv           = argv,
 438                 .envp           = envp,
 439                 .retval         = 0,
 440         };
 441         struct file *f;
 442
 443         if (!khelper_wq)
 444                 return -EBUSY;
 445
 446         if (path[0] == '\0')
 447                 return 0;
 448
 449         f = create_write_pipe();
 450         if (IS_ERR(f))
 451                 return PTR_ERR(f);
 452         *filp = f;
 453
 454         f = create_read_pipe(f);
 455         if (IS_ERR(f)) {
 456                 free_write_pipe(*filp);
 457                 return PTR_ERR(f);
 458         }
 459         sub_info.stdin = f;
 460
 461         queue_work(khelper_wq, &sub_info.work);
 462         wait_for_completion(&done);
 463         return sub_info.retval;
 464 }
 465 EXPORT_SYMBOL(call_usermodehelper_pipe);
 466
 467 void __init usermodehelper_init(void)
 468 {
 469         khelper_wq = create_singlethread_workqueue("khelper");
 470         BUG_ON(!khelper_wq);
 471 }