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         spin_lock_irq(&current->sighand->siglock);
 139         old_session = __install_session_keyring(current, new_session);
 140         flush_signal_handlers(current, 1);
 141         sigemptyset(&current->blocked);
 142         recalc_sigpending();
 143         spin_unlock_irq(&current->sighand->siglock);
 144
 145         key_put(old_session);
 146
 147         /* Install input pipe when needed */
 148         if (sub_info->stdin) {
 149                 struct files_struct *f = current->files;
 150                 struct fdtable *fdt;
 151                 /* no races because files should be private here */
 152                 sys_close(0);
 153                 fd_install(0, sub_info->stdin);
 154                 spin_lock(&f->file_lock);
 155                 fdt = files_fdtable(f);
 156                 FD_SET(0, fdt->open_fds);
 157                 FD_CLR(0, fdt->close_on_exec);
 158                 spin_unlock(&f->file_lock);
 159
 160                 /* and disallow core files too */
 161                 current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
 162         }
 163
 164         /* We can run anywhere, unlike our parent keventd(). */
 165         set_cpus_allowed(current, CPU_MASK_ALL);
 166
 167         /*
 168          * Our parent is keventd, which runs with elevated scheduling priority.
 169          * Avoid propagating that into the userspace child.
 170          */
 171         set_user_nice(current, 0);
 172
 173         retval = -EPERM;
 174         if (current->fs->root)
 175                 retval = kernel_execve(sub_info->path,
 176                                 sub_info->argv, sub_info->envp);
 177
 178         /* Exec failed? */
 179         sub_info->retval = retval;
 180         do_exit(0);
 181 }
 182
 183 /* Keventd can't block, but this (a child) can. */
 184 static int wait_for_helper(void *data)
 185 {
 186         struct subprocess_info *sub_info = data;
 187         pid_t pid;
 188
 189         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 190          * populate the status, but will return -ECHILD. */
 191         allow_signal(SIGCHLD);
 192
 193         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 194         if (pid < 0) {
 195                 sub_info->retval = pid;
 196         } else {
 197                 int ret;
 198
 199                 /*
 200                  * Normally it is bogus to call wait4() from in-kernel because
 201                  * wait4() wants to write the exit code to a userspace address.
 202                  * But wait_for_helper() always runs as keventd, and put_user()
 203                  * to a kernel address works OK for kernel threads, due to their
 204                  * having an mm_segment_t which spans the entire address space.
 205                  *
 206                  * Thus the __user pointer cast is valid here.
 207                  */
 208                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 209
 210                 /*
 211                  * If ret is 0, either ____call_usermodehelper failed and the
 212                  * real error code is already in sub_info->retval or
 213                  * sub_info->retval is 0 anyway, so don't mess with it then.
 214                  */
 215                 if (ret)
 216                         sub_info->retval = ret;
 217         }
 218
 219         if (sub_info->wait < 0)
 220                 kfree(sub_info);
 221         else
 222                 complete(sub_info->complete);
 223         return 0;
 224 }
 225
 226 /* This is run by khelper thread  */
 227 static void __call_usermodehelper(struct work_struct *work)
 228 {
 229         struct subprocess_info *sub_info =
 230                 container_of(work, struct subprocess_info, work);
 231         pid_t pid;
 232         int wait = sub_info->wait;
 233
 234         /* CLONE_VFORK: wait until the usermode helper has execve'd
 235          * successfully We need the data structures to stay around
 236          * until that is done.  */
 237         if (wait)
 238                 pid = kernel_thread(wait_for_helper, sub_info,
 239                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 240         else
 241                 pid = kernel_thread(____call_usermodehelper, sub_info,
 242                                     CLONE_VFORK | SIGCHLD);
 243
 244         if (wait < 0)
 245                 return;
 246
 247         if (pid < 0) {
 248                 sub_info->retval = pid;
 249                 complete(sub_info->complete);
 250         } else if (!wait)
 251                 complete(sub_info->complete);
 252 }
 253
 254 /**
 255  * call_usermodehelper_keys - start a usermode application
 256  * @path: pathname for the application
 257  * @argv: null-terminated argument list
 258  * @envp: null-terminated environment list
 259  * @session_keyring: session keyring for process (NULL for an empty keyring)
 260  * @wait: wait for the application to finish and return status.
 261  *        when -1 don't wait at all, but you get no useful error back when
 262  *        the program couldn't be exec'ed. This makes it safe to call
 263  *        from interrupt context.
 264  *
 265  * Runs a user-space application.  The application is started
 266  * asynchronously if wait is not set, and runs as a child of keventd.
 267  * (ie. it runs with full root capabilities).
 268  *
 269  * Must be called from process context.  Returns a negative error code
 270  * if program was not execed successfully, or 0.
 271  */
 272 int call_usermodehelper_keys(char *path, char **argv, char **envp,
 273                              struct key *session_keyring, int wait)
 274 {
 275         DECLARE_COMPLETION_ONSTACK(done);
 276         struct subprocess_info *sub_info;
 277         int retval;
 278
 279         if (!khelper_wq)
 280                 return -EBUSY;
 281
 282         if (path[0] == '\0')
 283                 return 0;
 284
 285         sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
 286         if (!sub_info)
 287                 return -ENOMEM;
 288
 289         INIT_WORK(&sub_info->work, __call_usermodehelper);
 290         sub_info->complete = &done;
 291         sub_info->path = path;
 292         sub_info->argv = argv;
 293         sub_info->envp = envp;
 294         sub_info->ring = session_keyring;
 295         sub_info->wait = wait;
 296
 297         queue_work(khelper_wq, &sub_info->work);
 298         if (wait < 0) /* task has freed sub_info */
 299                 return 0;
 300         wait_for_completion(&done);
 301         retval = sub_info->retval;
 302         kfree(sub_info);
 303         return retval;
 304 }
 305 EXPORT_SYMBOL(call_usermodehelper_keys);
 306
 307 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 308                              struct file **filp)
 309 {
 310         DECLARE_COMPLETION(done);
 311         struct subprocess_info sub_info = {
 312                 .work           = __WORK_INITIALIZER(sub_info.work,
 313                                                      __call_usermodehelper),
 314                 .complete       = &done,
 315                 .path           = path,
 316                 .argv           = argv,
 317                 .envp           = envp,
 318                 .retval         = 0,
 319         };
 320         struct file *f;
 321
 322         if (!khelper_wq)
 323                 return -EBUSY;
 324
 325         if (path[0] == '\0')
 326                 return 0;
 327
 328         f = create_write_pipe();
 329         if (IS_ERR(f))
 330                 return PTR_ERR(f);
 331         *filp = f;
 332
 333         f = create_read_pipe(f);
 334         if (IS_ERR(f)) {
 335                 free_write_pipe(*filp);
 336                 return PTR_ERR(f);
 337         }
 338         sub_info.stdin = f;
 339
 340         queue_work(khelper_wq, &sub_info.work);
 341         wait_for_completion(&done);
 342         return sub_info.retval;
 343 }
 344 EXPORT_SYMBOL(call_usermodehelper_pipe);
 345
 346 void __init usermodehelper_init(void)
 347 {
 348         khelper_wq = create_singlethread_workqueue("khelper");
 349         BUG_ON(!khelper_wq);
 350 }