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         int wait;
 123         int retval;
 124         struct file *stdin;
 125 };
 126
 127 /*
 128  * This is the task which runs the usermode application
 129  */
 130 static int ____call_usermodehelper(void *data)
 131 {
 132         struct subprocess_info *sub_info = data;
 133         struct key *new_session, *old_session;
 134         int retval;
 135
 136         /* Unblock all signals and set the session keyring. */
 137         new_session = key_get(sub_info->ring);
 138         flush_signals(current);
 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 /* Keventd can't block, but this (a child) can. */
 185 static int wait_for_helper(void *data)
 186 {
 187         struct subprocess_info *sub_info = data;
 188         pid_t pid;
 189         struct k_sigaction sa;
 190
 191         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 192          * populate the status, but will return -ECHILD. */
 193         sa.sa.sa_handler = SIG_IGN;
 194         sa.sa.sa_flags = 0;
 195         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 196         do_sigaction(SIGCHLD, &sa, NULL);
 197         allow_signal(SIGCHLD);
 198
 199         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 200         if (pid < 0) {
 201                 sub_info->retval = pid;
 202         } else {
 203                 int ret;
 204
 205                 /*
 206                  * Normally it is bogus to call wait4() from in-kernel because
 207                  * wait4() wants to write the exit code to a userspace address.
 208                  * But wait_for_helper() always runs as keventd, and put_user()
 209                  * to a kernel address works OK for kernel threads, due to their
 210                  * having an mm_segment_t which spans the entire address space.
 211                  *
 212                  * Thus the __user pointer cast is valid here.
 213                  */
 214                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 215
 216                 /*
 217                  * If ret is 0, either ____call_usermodehelper failed and the
 218                  * real error code is already in sub_info->retval or
 219                  * sub_info->retval is 0 anyway, so don't mess with it then.
 220                  */
 221                 if (ret)
 222                         sub_info->retval = ret;
 223         }
 224
 225         if (sub_info->wait < 0)
 226                 kfree(sub_info);
 227         else
 228                 complete(sub_info->complete);
 229         return 0;
 230 }
 231
 232 /* This is run by khelper thread  */
 233 static void __call_usermodehelper(struct work_struct *work)
 234 {
 235         struct subprocess_info *sub_info =
 236                 container_of(work, struct subprocess_info, work);
 237         pid_t pid;
 238         int wait = sub_info->wait;
 239
 240         /* CLONE_VFORK: wait until the usermode helper has execve'd
 241          * successfully We need the data structures to stay around
 242          * until that is done.  */
 243         if (wait)
 244                 pid = kernel_thread(wait_for_helper, sub_info,
 245                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 246         else
 247                 pid = kernel_thread(____call_usermodehelper, sub_info,
 248                                     CLONE_VFORK | SIGCHLD);
 249
 250         if (wait < 0)
 251                 return;
 252
 253         if (pid < 0) {
 254                 sub_info->retval = pid;
 255                 complete(sub_info->complete);
 256         } else if (!wait)
 257                 complete(sub_info->complete);
 258 }
 259
 260 /**
 261  * call_usermodehelper_keys - start a usermode application
 262  * @path: pathname for the application
 263  * @argv: null-terminated argument list
 264  * @envp: null-terminated environment list
 265  * @session_keyring: session keyring for process (NULL for an empty keyring)
 266  * @wait: wait for the application to finish and return status.
 267  *        when -1 don't wait at all, but you get no useful error back when
 268  *        the program couldn't be exec'ed. This makes it safe to call
 269  *        from interrupt context.
 270  *
 271  * Runs a user-space application.  The application is started
 272  * asynchronously if wait is not set, and runs as a child of keventd.
 273  * (ie. it runs with full root capabilities).
 274  *
 275  * Must be called from process context.  Returns a negative error code
 276  * if program was not execed successfully, or 0.
 277  */
 278 int call_usermodehelper_keys(char *path, char **argv, char **envp,
 279                              struct key *session_keyring, int wait)
 280 {
 281         DECLARE_COMPLETION_ONSTACK(done);
 282         struct subprocess_info *sub_info;
 283         int retval;
 284
 285         if (!khelper_wq)
 286                 return -EBUSY;
 287
 288         if (path[0] == '\0')
 289                 return 0;
 290
 291         sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
 292         if (!sub_info)
 293                 return -ENOMEM;
 294
 295         INIT_WORK(&sub_info->work, __call_usermodehelper);
 296         sub_info->complete = &done;
 297         sub_info->path = path;
 298         sub_info->argv = argv;
 299         sub_info->envp = envp;
 300         sub_info->ring = session_keyring;
 301         sub_info->wait = wait;
 302
 303         queue_work(khelper_wq, &sub_info->work);
 304         if (wait < 0) /* task has freed sub_info */
 305                 return 0;
 306         wait_for_completion(&done);
 307         retval = sub_info->retval;
 308         kfree(sub_info);
 309         return retval;
 310 }
 311 EXPORT_SYMBOL(call_usermodehelper_keys);
 312
 313 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 314                              struct file **filp)
 315 {
 316         DECLARE_COMPLETION(done);
 317         struct subprocess_info sub_info = {
 318                 .work           = __WORK_INITIALIZER(sub_info.work,
 319                                                      __call_usermodehelper),
 320                 .complete       = &done,
 321                 .path           = path,
 322                 .argv           = argv,
 323                 .envp           = envp,
 324                 .retval         = 0,
 325         };
 326         struct file *f;
 327
 328         if (!khelper_wq)
 329                 return -EBUSY;
 330
 331         if (path[0] == '\0')
 332                 return 0;
 333
 334         f = create_write_pipe();
 335         if (IS_ERR(f))
 336                 return PTR_ERR(f);
 337         *filp = f;
 338
 339         f = create_read_pipe(f);
 340         if (IS_ERR(f)) {
 341                 free_write_pipe(*filp);
 342                 return PTR_ERR(f);
 343         }
 344         sub_info.stdin = f;
 345
 346         queue_work(khelper_wq, &sub_info.work);
 347         wait_for_completion(&done);
 348         return sub_info.retval;
 349 }
 350 EXPORT_SYMBOL(call_usermodehelper_pipe);
 351
 352 void __init usermodehelper_init(void)
 353 {
 354         khelper_wq = create_singlethread_workqueue("khelper");
 355         BUG_ON(!khelper_wq);
 356 }