linux/kernel/kmod.c
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   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/completion.h>
  28#include <linux/cred.h>
  29#include <linux/file.h>
  30#include <linux/fdtable.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 <linux/notifier.h>
  38#include <linux/suspend.h>
  39#include <asm/uaccess.h>
  40
  41#include <trace/events/module.h>
  42
  43extern int max_threads;
  44
  45static struct workqueue_struct *khelper_wq;
  46
  47#define CAP_BSET        (void *)1
  48#define CAP_PI          (void *)2
  49
  50static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
  51static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
  52static DEFINE_SPINLOCK(umh_sysctl_lock);
  53
  54#ifdef CONFIG_MODULES
  55
  56/*
  57        modprobe_path is set via /proc/sys.
  58*/
  59char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  60
  61/**
  62 * __request_module - try to load a kernel module
  63 * @wait: wait (or not) for the operation to complete
  64 * @fmt: printf style format string for the name of the module
  65 * @...: arguments as specified in the format string
  66 *
  67 * Load a module using the user mode module loader. The function returns
  68 * zero on success or a negative errno code on failure. Note that a
  69 * successful module load does not mean the module did not then unload
  70 * and exit on an error of its own. Callers must check that the service
  71 * they requested is now available not blindly invoke it.
  72 *
  73 * If module auto-loading support is disabled then this function
  74 * becomes a no-operation.
  75 */
  76int __request_module(bool wait, const char *fmt, ...)
  77{
  78        va_list args;
  79        char module_name[MODULE_NAME_LEN];
  80        unsigned int max_modprobes;
  81        int ret;
  82        char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  83        static char *envp[] = { "HOME=/",
  84                                "TERM=linux",
  85                                "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  86                                NULL };
  87        static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  88#define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  89        static int kmod_loop_msg;
  90
  91        va_start(args, fmt);
  92        ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  93        va_end(args);
  94        if (ret >= MODULE_NAME_LEN)
  95                return -ENAMETOOLONG;
  96
  97        ret = security_kernel_module_request(module_name);
  98        if (ret)
  99                return ret;
 100
 101        /* If modprobe needs a service that is in a module, we get a recursive
 102         * loop.  Limit the number of running kmod threads to max_threads/2 or
 103         * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 104         * would be to run the parents of this process, counting how many times
 105         * kmod was invoked.  That would mean accessing the internals of the
 106         * process tables to get the command line, proc_pid_cmdline is static
 107         * and it is not worth changing the proc code just to handle this case. 
 108         * KAO.
 109         *
 110         * "trace the ppid" is simple, but will fail if someone's
 111         * parent exits.  I think this is as good as it gets. --RR
 112         */
 113        max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 114        atomic_inc(&kmod_concurrent);
 115        if (atomic_read(&kmod_concurrent) > max_modprobes) {
 116                /* We may be blaming an innocent here, but unlikely */
 117                if (kmod_loop_msg < 5) {
 118                        printk(KERN_ERR
 119                               "request_module: runaway loop modprobe %s\n",
 120                               module_name);
 121                        kmod_loop_msg++;
 122                }
 123                atomic_dec(&kmod_concurrent);
 124                return -ENOMEM;
 125        }
 126
 127        trace_module_request(module_name, wait, _RET_IP_);
 128
 129        ret = call_usermodehelper_fns(modprobe_path, argv, envp,
 130                        wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC,
 131                        NULL, NULL, NULL);
 132
 133        atomic_dec(&kmod_concurrent);
 134        return ret;
 135}
 136EXPORT_SYMBOL(__request_module);
 137#endif /* CONFIG_MODULES */
 138
 139/*
 140 * This is the task which runs the usermode application
 141 */
 142static int ____call_usermodehelper(void *data)
 143{
 144        struct subprocess_info *sub_info = data;
 145        struct cred *new;
 146        int retval;
 147
 148        spin_lock_irq(&current->sighand->siglock);
 149        flush_signal_handlers(current, 1);
 150        spin_unlock_irq(&current->sighand->siglock);
 151
 152        /* We can run anywhere, unlike our parent keventd(). */
 153        set_cpus_allowed_ptr(current, cpu_all_mask);
 154
 155        /*
 156         * Our parent is keventd, which runs with elevated scheduling priority.
 157         * Avoid propagating that into the userspace child.
 158         */
 159        set_user_nice(current, 0);
 160
 161        retval = -ENOMEM;
 162        new = prepare_kernel_cred(current);
 163        if (!new)
 164                goto fail;
 165
 166        spin_lock(&umh_sysctl_lock);
 167        new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
 168        new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
 169                                             new->cap_inheritable);
 170        spin_unlock(&umh_sysctl_lock);
 171
 172        if (sub_info->init) {
 173                retval = sub_info->init(sub_info, new);
 174                if (retval) {
 175                        abort_creds(new);
 176                        goto fail;
 177                }
 178        }
 179
 180        commit_creds(new);
 181
 182        retval = kernel_execve(sub_info->path,
 183                               (const char *const *)sub_info->argv,
 184                               (const char *const *)sub_info->envp);
 185
 186        /* Exec failed? */
 187fail:
 188        sub_info->retval = retval;
 189        do_exit(0);
 190}
 191
 192void call_usermodehelper_freeinfo(struct subprocess_info *info)
 193{
 194        if (info->cleanup)
 195                (*info->cleanup)(info);
 196        kfree(info);
 197}
 198EXPORT_SYMBOL(call_usermodehelper_freeinfo);
 199
 200/* Keventd can't block, but this (a child) can. */
 201static int wait_for_helper(void *data)
 202{
 203        struct subprocess_info *sub_info = data;
 204        pid_t pid;
 205
 206        /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 207        spin_lock_irq(&current->sighand->siglock);
 208        current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
 209        spin_unlock_irq(&current->sighand->siglock);
 210
 211        pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 212        if (pid < 0) {
 213                sub_info->retval = pid;
 214        } else {
 215                int ret = -ECHILD;
 216                /*
 217                 * Normally it is bogus to call wait4() from in-kernel because
 218                 * wait4() wants to write the exit code to a userspace address.
 219                 * But wait_for_helper() always runs as keventd, and put_user()
 220                 * to a kernel address works OK for kernel threads, due to their
 221                 * having an mm_segment_t which spans the entire address space.
 222                 *
 223                 * Thus the __user pointer cast is valid here.
 224                 */
 225                sys_wait4(pid, (int __user *)&ret, 0, NULL);
 226
 227                /*
 228                 * If ret is 0, either ____call_usermodehelper failed and the
 229                 * real error code is already in sub_info->retval or
 230                 * sub_info->retval is 0 anyway, so don't mess with it then.
 231                 */
 232                if (ret)
 233                        sub_info->retval = ret;
 234        }
 235
 236        complete(sub_info->complete);
 237        return 0;
 238}
 239
 240/* This is run by khelper thread  */
 241static void __call_usermodehelper(struct work_struct *work)
 242{
 243        struct subprocess_info *sub_info =
 244                container_of(work, struct subprocess_info, work);
 245        enum umh_wait wait = sub_info->wait;
 246        pid_t pid;
 247
 248        /* CLONE_VFORK: wait until the usermode helper has execve'd
 249         * successfully We need the data structures to stay around
 250         * until that is done.  */
 251        if (wait == UMH_WAIT_PROC)
 252                pid = kernel_thread(wait_for_helper, sub_info,
 253                                    CLONE_FS | CLONE_FILES | SIGCHLD);
 254        else
 255                pid = kernel_thread(____call_usermodehelper, sub_info,
 256                                    CLONE_VFORK | SIGCHLD);
 257
 258        switch (wait) {
 259        case UMH_NO_WAIT:
 260                call_usermodehelper_freeinfo(sub_info);
 261                break;
 262
 263        case UMH_WAIT_PROC:
 264                if (pid > 0)
 265                        break;
 266                /* FALLTHROUGH */
 267        case UMH_WAIT_EXEC:
 268                if (pid < 0)
 269                        sub_info->retval = pid;
 270                complete(sub_info->complete);
 271        }
 272}
 273
 274/*
 275 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 276 * (used for preventing user land processes from being created after the user
 277 * land has been frozen during a system-wide hibernation or suspend operation).
 278 */
 279static int usermodehelper_disabled = 1;
 280
 281/* Number of helpers running */
 282static atomic_t running_helpers = ATOMIC_INIT(0);
 283
 284/*
 285 * Wait queue head used by usermodehelper_pm_callback() to wait for all running
 286 * helpers to finish.
 287 */
 288static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 289
 290/*
 291 * Time to wait for running_helpers to become zero before the setting of
 292 * usermodehelper_disabled in usermodehelper_pm_callback() fails
 293 */
 294#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 295
 296/**
 297 * usermodehelper_disable - prevent new helpers from being started
 298 */
 299int usermodehelper_disable(void)
 300{
 301        long retval;
 302
 303        usermodehelper_disabled = 1;
 304        smp_mb();
 305        /*
 306         * From now on call_usermodehelper_exec() won't start any new
 307         * helpers, so it is sufficient if running_helpers turns out to
 308         * be zero at one point (it may be increased later, but that
 309         * doesn't matter).
 310         */
 311        retval = wait_event_timeout(running_helpers_waitq,
 312                                        atomic_read(&running_helpers) == 0,
 313                                        RUNNING_HELPERS_TIMEOUT);
 314        if (retval)
 315                return 0;
 316
 317        usermodehelper_disabled = 0;
 318        return -EAGAIN;
 319}
 320
 321/**
 322 * usermodehelper_enable - allow new helpers to be started again
 323 */
 324void usermodehelper_enable(void)
 325{
 326        usermodehelper_disabled = 0;
 327}
 328
 329/**
 330 * usermodehelper_is_disabled - check if new helpers are allowed to be started
 331 */
 332bool usermodehelper_is_disabled(void)
 333{
 334        return usermodehelper_disabled;
 335}
 336EXPORT_SYMBOL_GPL(usermodehelper_is_disabled);
 337
 338static void helper_lock(void)
 339{
 340        atomic_inc(&running_helpers);
 341        smp_mb__after_atomic_inc();
 342}
 343
 344static void helper_unlock(void)
 345{
 346        if (atomic_dec_and_test(&running_helpers))
 347                wake_up(&running_helpers_waitq);
 348}
 349
 350/**
 351 * call_usermodehelper_setup - prepare to call a usermode helper
 352 * @path: path to usermode executable
 353 * @argv: arg vector for process
 354 * @envp: environment for process
 355 * @gfp_mask: gfp mask for memory allocation
 356 *
 357 * Returns either %NULL on allocation failure, or a subprocess_info
 358 * structure.  This should be passed to call_usermodehelper_exec to
 359 * exec the process and free the structure.
 360 */
 361struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 362                                                  char **envp, gfp_t gfp_mask)
 363{
 364        struct subprocess_info *sub_info;
 365        sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 366        if (!sub_info)
 367                goto out;
 368
 369        INIT_WORK(&sub_info->work, __call_usermodehelper);
 370        sub_info->path = path;
 371        sub_info->argv = argv;
 372        sub_info->envp = envp;
 373  out:
 374        return sub_info;
 375}
 376EXPORT_SYMBOL(call_usermodehelper_setup);
 377
 378/**
 379 * call_usermodehelper_setfns - set a cleanup/init function
 380 * @info: a subprocess_info returned by call_usermodehelper_setup
 381 * @cleanup: a cleanup function
 382 * @init: an init function
 383 * @data: arbitrary context sensitive data
 384 *
 385 * The init function is used to customize the helper process prior to
 386 * exec.  A non-zero return code causes the process to error out, exit,
 387 * and return the failure to the calling process
 388 *
 389 * The cleanup function is just before ethe subprocess_info is about to
 390 * be freed.  This can be used for freeing the argv and envp.  The
 391 * Function must be runnable in either a process context or the
 392 * context in which call_usermodehelper_exec is called.
 393 */
 394void call_usermodehelper_setfns(struct subprocess_info *info,
 395                    int (*init)(struct subprocess_info *info, struct cred *new),
 396                    void (*cleanup)(struct subprocess_info *info),
 397                    void *data)
 398{
 399        info->cleanup = cleanup;
 400        info->init = init;
 401        info->data = data;
 402}
 403EXPORT_SYMBOL(call_usermodehelper_setfns);
 404
 405/**
 406 * call_usermodehelper_exec - start a usermode application
 407 * @sub_info: information about the subprocessa
 408 * @wait: wait for the application to finish and return status.
 409 *        when -1 don't wait at all, but you get no useful error back when
 410 *        the program couldn't be exec'ed. This makes it safe to call
 411 *        from interrupt context.
 412 *
 413 * Runs a user-space application.  The application is started
 414 * asynchronously if wait is not set, and runs as a child of keventd.
 415 * (ie. it runs with full root capabilities).
 416 */
 417int call_usermodehelper_exec(struct subprocess_info *sub_info,
 418                             enum umh_wait wait)
 419{
 420        DECLARE_COMPLETION_ONSTACK(done);
 421        int retval = 0;
 422
 423        helper_lock();
 424        if (sub_info->path[0] == '\0')
 425                goto out;
 426
 427        if (!khelper_wq || usermodehelper_disabled) {
 428                retval = -EBUSY;
 429                goto out;
 430        }
 431
 432        sub_info->complete = &done;
 433        sub_info->wait = wait;
 434
 435        queue_work(khelper_wq, &sub_info->work);
 436        if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 437                goto unlock;
 438        wait_for_completion(&done);
 439        retval = sub_info->retval;
 440
 441out:
 442        call_usermodehelper_freeinfo(sub_info);
 443unlock:
 444        helper_unlock();
 445        return retval;
 446}
 447EXPORT_SYMBOL(call_usermodehelper_exec);
 448
 449static int proc_cap_handler(struct ctl_table *table, int write,
 450                         void __user *buffer, size_t *lenp, loff_t *ppos)
 451{
 452        struct ctl_table t;
 453        unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
 454        kernel_cap_t new_cap;
 455        int err, i;
 456
 457        if (write && (!capable(CAP_SETPCAP) ||
 458                      !capable(CAP_SYS_MODULE)))
 459                return -EPERM;
 460
 461        /*
 462         * convert from the global kernel_cap_t to the ulong array to print to
 463         * userspace if this is a read.
 464         */
 465        spin_lock(&umh_sysctl_lock);
 466        for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
 467                if (table->data == CAP_BSET)
 468                        cap_array[i] = usermodehelper_bset.cap[i];
 469                else if (table->data == CAP_PI)
 470                        cap_array[i] = usermodehelper_inheritable.cap[i];
 471                else
 472                        BUG();
 473        }
 474        spin_unlock(&umh_sysctl_lock);
 475
 476        t = *table;
 477        t.data = &cap_array;
 478
 479        /*
 480         * actually read or write and array of ulongs from userspace.  Remember
 481         * these are least significant 32 bits first
 482         */
 483        err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
 484        if (err < 0)
 485                return err;
 486
 487        /*
 488         * convert from the sysctl array of ulongs to the kernel_cap_t
 489         * internal representation
 490         */
 491        for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
 492                new_cap.cap[i] = cap_array[i];
 493
 494        /*
 495         * Drop everything not in the new_cap (but don't add things)
 496         */
 497        spin_lock(&umh_sysctl_lock);
 498        if (write) {
 499                if (table->data == CAP_BSET)
 500                        usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 501                if (table->data == CAP_PI)
 502                        usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
 503        }
 504        spin_unlock(&umh_sysctl_lock);
 505
 506        return 0;
 507}
 508
 509struct ctl_table usermodehelper_table[] = {
 510        {
 511                .procname       = "bset",
 512                .data           = CAP_BSET,
 513                .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 514                .mode           = 0600,
 515                .proc_handler   = proc_cap_handler,
 516        },
 517        {
 518                .procname       = "inheritable",
 519                .data           = CAP_PI,
 520                .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 521                .mode           = 0600,
 522                .proc_handler   = proc_cap_handler,
 523        },
 524        { }
 525};
 526
 527void __init usermodehelper_init(void)
 528{
 529        khelper_wq = create_singlethread_workqueue("khelper");
 530        BUG_ON(!khelper_wq);
 531}
 532
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