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/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 <asm/uaccess.h>
  37
  38 extern int max_threads;
  39
  40 static struct workqueue_struct *khelper_wq;
  41
  42 #ifdef CONFIG_KMOD
  43
  44 /*
  45         modprobe_path is set via /proc/sys.
  46 */
  47 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  48
  49 /**
  50  * request_module - try to load a kernel module
  51  * @fmt:     printf style format string for the name of the module
  52  * @varargs: arguements as specified in the format string
  53  *
  54  * Load a module using the user mode module loader. The function returns
  55  * zero on success or a negative errno code on failure. Note that a
  56  * successful module load does not mean the module did not then unload
  57  * and exit on an error of its own. Callers must check that the service
  58  * they requested is now available not blindly invoke it.
  59  *
  60  * If module auto-loading support is disabled then this function
  61  * becomes a no-operation.
  62  */
  63 int request_module(const char *fmt, ...)
  64 {
  65         va_list args;
  66         char module_name[MODULE_NAME_LEN];
  67         unsigned int max_modprobes;
  68         int ret;
  69         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  70         static char *envp[] = { "HOME=/",
  71                                 "TERM=linux",
  72                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  73                                 NULL };
  74         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  75 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  76         static int kmod_loop_msg;
  77
  78         va_start(args, fmt);
  79         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  80         va_end(args);
  81         if (ret >= MODULE_NAME_LEN)
  82                 return -ENAMETOOLONG;
  83
  84         /* If modprobe needs a service that is in a module, we get a recursive
  85          * loop.  Limit the number of running kmod threads to max_threads/2 or
  86          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  87          * would be to run the parents of this process, counting how many times
  88          * kmod was invoked.  That would mean accessing the internals of the
  89          * process tables to get the command line, proc_pid_cmdline is static
  90          * and it is not worth changing the proc code just to handle this case.
  91          * KAO.
  92          *
  93          * "trace the ppid" is simple, but will fail if someone's
  94          * parent exits.  I think this is as good as it gets. --RR
  95          */
  96         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
  97         atomic_inc(&kmod_concurrent);
  98         if (atomic_read(&kmod_concurrent) > max_modprobes) {
  99                 /* We may be blaming an innocent here, but unlikely */
 100                 if (kmod_loop_msg++ < 5)
 101                         printk(KERN_ERR
 102                                "request_module: runaway loop modprobe %s\n",
 103                                module_name);
 104                 atomic_dec(&kmod_concurrent);
 105                 return -ENOMEM;
 106         }
 107
 108         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 109         atomic_dec(&kmod_concurrent);
 110         return ret;
 111 }
 112 EXPORT_SYMBOL(request_module);
 113 #endif /* CONFIG_KMOD */
 114
 115 struct subprocess_info {
 116         struct work_struct work;
 117         struct completion *complete;
 118         char *path;
 119         char **argv;
 120         char **envp;
 121         struct key *ring;
 122         enum umh_wait wait;
 123         int retval;
 124         struct file *stdin;
 125         void (*cleanup)(char **argv, char **envp);
 126 };
 127
 128 /*
 129  * This is the task which runs the usermode application
 130  */
 131 static int ____call_usermodehelper(void *data)
 132 {
 133         struct subprocess_info *sub_info = data;
 134         struct key *new_session, *old_session;
 135         int retval;
 136
 137         /* Unblock all signals and set the session keyring. */
 138         new_session = key_get(sub_info->ring);
 139         spin_lock_irq(&current->sighand->siglock);
 140         old_session = __install_session_keyring(current, new_session);
 141         flush_signal_handlers(current, 1);
 142         sigemptyset(&current->blocked);
 143         recalc_sigpending();
 144         spin_unlock_irq(&current->sighand->siglock);
 145
 146         key_put(old_session);
 147
 148         /* Install input pipe when needed */
 149         if (sub_info->stdin) {
 150                 struct files_struct *f = current->files;
 151                 struct fdtable *fdt;
 152                 /* no races because files should be private here */
 153                 sys_close(0);
 154                 fd_install(0, sub_info->stdin);
 155                 spin_lock(&f->file_lock);
 156                 fdt = files_fdtable(f);
 157                 FD_SET(0, fdt->open_fds);
 158                 FD_CLR(0, fdt->close_on_exec);
 159                 spin_unlock(&f->file_lock);
 160
 161                 /* and disallow core files too */
 162                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 163         }
 164
 165         /* We can run anywhere, unlike our parent keventd(). */
 166         set_cpus_allowed(current, CPU_MASK_ALL);
 167
 168         /*
 169          * Our parent is keventd, which runs with elevated scheduling priority.
 170          * Avoid propagating that into the userspace child.
 171          */
 172         set_user_nice(current, 0);
 173
 174         retval = -EPERM;
 175         if (current->fs->root)
 176                 retval = kernel_execve(sub_info->path,
 177                                 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 /**
 269  * call_usermodehelper_setup - prepare to call a usermode helper
 270  * @path - path to usermode executable
 271  * @argv - arg vector for process
 272  * @envp - environment for process
 273  *
 274  * Returns either NULL on allocation failure, or a subprocess_info
 275  * structure.  This should be passed to call_usermodehelper_exec to
 276  * exec the process and free the structure.
 277  */
 278 struct subprocess_info *call_usermodehelper_setup(char *path,
 279                                                   char **argv, char **envp)
 280 {
 281         struct subprocess_info *sub_info;
 282         sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
 283         if (!sub_info)
 284                 goto out;
 285
 286         INIT_WORK(&sub_info->work, __call_usermodehelper);
 287         sub_info->path = path;
 288         sub_info->argv = argv;
 289         sub_info->envp = envp;
 290
 291   out:
 292         return sub_info;
 293 }
 294 EXPORT_SYMBOL(call_usermodehelper_setup);
 295
 296 /**
 297  * call_usermodehelper_setkeys - set the session keys for usermode helper
 298  * @info: a subprocess_info returned by call_usermodehelper_setup
 299  * @session_keyring: the session keyring for the process
 300  */
 301 void call_usermodehelper_setkeys(struct subprocess_info *info,
 302                                  struct key *session_keyring)
 303 {
 304         info->ring = session_keyring;
 305 }
 306 EXPORT_SYMBOL(call_usermodehelper_setkeys);
 307
 308 /**
 309  * call_usermodehelper_setcleanup - set a cleanup function
 310  * @info: a subprocess_info returned by call_usermodehelper_setup
 311  * @cleanup: a cleanup function
 312  *
 313  * The cleanup function is just befor ethe subprocess_info is about to
 314  * be freed.  This can be used for freeing the argv and envp.  The
 315  * Function must be runnable in either a process context or the
 316  * context in which call_usermodehelper_exec is called.
 317  */
 318 void call_usermodehelper_setcleanup(struct subprocess_info *info,
 319                                     void (*cleanup)(char **argv, char **envp))
 320 {
 321         info->cleanup = cleanup;
 322 }
 323 EXPORT_SYMBOL(call_usermodehelper_setcleanup);
 324
 325 /**
 326  * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
 327  * @sub_info: a subprocess_info returned by call_usermodehelper_setup
 328  * @filp: set to the write-end of a pipe
 329  *
 330  * This constructs a pipe, and sets the read end to be the stdin of the
 331  * subprocess, and returns the write-end in *@filp.
 332  */
 333 int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
 334                                   struct file **filp)
 335 {
 336         struct file *f;
 337
 338         f = create_write_pipe();
 339         if (IS_ERR(f))
 340                 return PTR_ERR(f);
 341         *filp = f;
 342
 343         f = create_read_pipe(f);
 344         if (IS_ERR(f)) {
 345                 free_write_pipe(*filp);
 346                 return PTR_ERR(f);
 347         }
 348         sub_info->stdin = f;
 349
 350         return 0;
 351 }
 352 EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
 353
 354 /**
 355  * call_usermodehelper_exec - start a usermode application
 356  * @sub_info: information about the subprocessa
 357  * @wait: wait for the application to finish and return status.
 358  *        when -1 don't wait at all, but you get no useful error back when
 359  *        the program couldn't be exec'ed. This makes it safe to call
 360  *        from interrupt context.
 361  *
 362  * Runs a user-space application.  The application is started
 363  * asynchronously if wait is not set, and runs as a child of keventd.
 364  * (ie. it runs with full root capabilities).
 365  */
 366 int call_usermodehelper_exec(struct subprocess_info *sub_info,
 367                              enum umh_wait wait)
 368 {
 369         DECLARE_COMPLETION_ONSTACK(done);
 370         int retval;
 371
 372         if (sub_info->path[0] == '\0') {
 373                 retval = 0;
 374                 goto out;
 375         }
 376
 377         if (!khelper_wq) {
 378                 retval = -EBUSY;
 379                 goto out;
 380         }
 381
 382         sub_info->complete = &done;
 383         sub_info->wait = wait;
 384
 385         queue_work(khelper_wq, &sub_info->work);
 386         if (wait == UMH_NO_WAIT) /* task has freed sub_info */
 387                 return 0;
 388         wait_for_completion(&done);
 389         retval = sub_info->retval;
 390
 391   out:
 392         call_usermodehelper_freeinfo(sub_info);
 393         return retval;
 394 }
 395 EXPORT_SYMBOL(call_usermodehelper_exec);
 396
 397 /**
 398  * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
 399  * @path: path to usermode executable
 400  * @argv: arg vector for process
 401  * @envp: environment for process
 402  * @filp: set to the write-end of a pipe
 403  *
 404  * This is a simple wrapper which executes a usermode-helper function
 405  * with a pipe as stdin.  It is implemented entirely in terms of
 406  * lower-level call_usermodehelper_* functions.
 407  */
 408 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 409                              struct file **filp)
 410 {
 411         struct subprocess_info *sub_info;
 412         int ret;
 413
 414         sub_info = call_usermodehelper_setup(path, argv, envp);
 415         if (sub_info == NULL)
 416                 return -ENOMEM;
 417
 418         ret = call_usermodehelper_stdinpipe(sub_info, filp);
 419         if (ret < 0)
 420                 goto out;
 421
 422         return call_usermodehelper_exec(sub_info, 1);
 423
 424   out:
 425         call_usermodehelper_freeinfo(sub_info);
 426         return ret;
 427 }
 428 EXPORT_SYMBOL(call_usermodehelper_pipe);
 429
 430 void __init usermodehelper_init(void)
 431 {
 432         khelper_wq = create_singlethread_workqueue("khelper");
 433         BUG_ON(!khelper_wq);
 434 }