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