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/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 max_threads;
  40
  41 static struct workqueue_struct *khelper_wq;
  42
  43 #ifdef CONFIG_KMOD
  44
  45 /*
  46         modprobe_path is set via /proc/sys.
  47 */
  48 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  49
  50 /**
  51  * request_module - try to load a kernel module
  52  * @fmt:     printf style format string for the name of the module
  53  * @varargs: arguements as specified in the format string
  54  *
  55  * Load a module using the user mode module loader. The function returns
  56  * zero on success or a negative errno code on failure. Note that a
  57  * successful module load does not mean the module did not then unload
  58  * and exit on an error of its own. Callers must check that the service
  59  * they requested is now available not blindly invoke it.
  60  *
  61  * If module auto-loading support is disabled then this function
  62  * becomes a no-operation.
  63  */
  64 int request_module(const char *fmt, ...)
  65 {
  66         va_list args;
  67         char module_name[MODULE_NAME_LEN];
  68         unsigned int max_modprobes;
  69         int ret;
  70         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  71         static char *envp[] = { "HOME=/",
  72                                 "TERM=linux",
  73                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  74                                 NULL };
  75         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  76 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  77         static int kmod_loop_msg;
  78
  79         va_start(args, fmt);
  80         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  81         va_end(args);
  82         if (ret >= MODULE_NAME_LEN)
  83                 return -ENAMETOOLONG;
  84
  85         /* If modprobe needs a service that is in a module, we get a recursive
  86          * loop.  Limit the number of running kmod threads to max_threads/2 or
  87          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  88          * would be to run the parents of this process, counting how many times
  89          * kmod was invoked.  That would mean accessing the internals of the
  90          * process tables to get the command line, proc_pid_cmdline is static
  91          * and it is not worth changing the proc code just to handle this case.
  92          * KAO.
  93          *
  94          * "trace the ppid" is simple, but will fail if someone's
  95          * parent exits.  I think this is as good as it gets. --RR
  96          */
  97         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
  98         atomic_inc(&kmod_concurrent);
  99         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 100                 /* We may be blaming an innocent here, but unlikely */
 101                 if (kmod_loop_msg++ < 5)
 102                         printk(KERN_ERR
 103                                "request_module: runaway loop modprobe %s\n",
 104                                module_name);
 105                 atomic_dec(&kmod_concurrent);
 106                 return -ENOMEM;
 107         }
 108
 109         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 110         atomic_dec(&kmod_concurrent);
 111         return ret;
 112 }
 113 EXPORT_SYMBOL(request_module);
 114 #endif /* CONFIG_KMOD */
 115
 116 struct subprocess_info {
 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         retval = -EPERM;
 169         if (current->fs->root)
 170                 retval = kernel_execve(sub_info->path,
 171                                 sub_info->argv, sub_info->envp);
 172
 173         /* Exec failed? */
 174         sub_info->retval = retval;
 175         do_exit(0);
 176 }
 177
 178 /* Keventd can't block, but this (a child) can. */
 179 static int wait_for_helper(void *data)
 180 {
 181         struct subprocess_info *sub_info = data;
 182         pid_t pid;
 183         struct k_sigaction sa;
 184
 185         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 186          * populate the status, but will return -ECHILD. */
 187         sa.sa.sa_handler = SIG_IGN;
 188         sa.sa.sa_flags = 0;
 189         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 190         do_sigaction(SIGCHLD, &sa, NULL);
 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         complete(sub_info->complete);
 220         return 0;
 221 }
 222
 223 /* This is run by khelper thread  */
 224 static void __call_usermodehelper(void *data)
 225 {
 226         struct subprocess_info *sub_info = data;
 227         pid_t pid;
 228         int wait = sub_info->wait;
 229
 230         /* CLONE_VFORK: wait until the usermode helper has execve'd
 231          * successfully We need the data structures to stay around
 232          * until that is done.  */
 233         if (wait)
 234                 pid = kernel_thread(wait_for_helper, sub_info,
 235                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 236         else
 237                 pid = kernel_thread(____call_usermodehelper, sub_info,
 238                                     CLONE_VFORK | SIGCHLD);
 239
 240         if (pid < 0) {
 241                 sub_info->retval = pid;
 242                 complete(sub_info->complete);
 243         } else if (!wait)
 244                 complete(sub_info->complete);
 245 }
 246
 247 /**
 248  * call_usermodehelper_keys - start a usermode application
 249  * @path: pathname for the application
 250  * @argv: null-terminated argument list
 251  * @envp: null-terminated environment list
 252  * @session_keyring: session keyring for process (NULL for an empty keyring)
 253  * @wait: wait for the application to finish and return status.
 254  *
 255  * Runs a user-space application.  The application is started
 256  * asynchronously if wait is not set, and runs as a child of keventd.
 257  * (ie. it runs with full root capabilities).
 258  *
 259  * Must be called from process context.  Returns a negative error code
 260  * if program was not execed successfully, or 0.
 261  */
 262 int call_usermodehelper_keys(char *path, char **argv, char **envp,
 263                              struct key *session_keyring, int wait)
 264 {
 265         DECLARE_COMPLETION_ONSTACK(done);
 266         struct subprocess_info sub_info = {
 267                 .complete       = &done,
 268                 .path           = path,
 269                 .argv           = argv,
 270                 .envp           = envp,
 271                 .ring           = session_keyring,
 272                 .wait           = wait,
 273                 .retval         = 0,
 274         };
 275         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 276
 277         if (!khelper_wq)
 278                 return -EBUSY;
 279
 280         if (path[0] == '\0')
 281                 return 0;
 282
 283         queue_work(khelper_wq, &work);
 284         wait_for_completion(&done);
 285         return sub_info.retval;
 286 }
 287 EXPORT_SYMBOL(call_usermodehelper_keys);
 288
 289 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 290                              struct file **filp)
 291 {
 292         DECLARE_COMPLETION(done);
 293         struct subprocess_info sub_info = {
 294                 .complete       = &done,
 295                 .path           = path,
 296                 .argv           = argv,
 297                 .envp           = envp,
 298                 .retval         = 0,
 299         };
 300         struct file *f;
 301         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 302
 303         if (!khelper_wq)
 304                 return -EBUSY;
 305
 306         if (path[0] == '\0')
 307                 return 0;
 308
 309         f = create_write_pipe();
 310         if (!f)
 311                 return -ENOMEM;
 312         *filp = f;
 313
 314         f = create_read_pipe(f);
 315         if (!f) {
 316                 free_write_pipe(*filp);
 317                 return -ENOMEM;
 318         }
 319         sub_info.stdin = f;
 320
 321         queue_work(khelper_wq, &work);
 322         wait_for_completion(&done);
 323         return sub_info.retval;
 324 }
 325 EXPORT_SYMBOL(call_usermodehelper_pipe);
 326
 327 void __init usermodehelper_init(void)
 328 {
 329         khelper_wq = create_singlethread_workqueue("khelper");
 330         BUG_ON(!khelper_wq);
 331 }