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 #define __KERNEL_SYSCALLS__
  22
  23 #include <linux/config.h>
  24 #include <linux/module.h>
  25 #include <linux/sched.h>
  26 #include <linux/syscalls.h>
  27 #include <linux/unistd.h>
  28 #include <linux/kmod.h>
  29 #include <linux/smp_lock.h>
  30 #include <linux/slab.h>
  31 #include <linux/namespace.h>
  32 #include <linux/completion.h>
  33 #include <linux/file.h>
  34 #include <linux/workqueue.h>
  35 #include <linux/security.h>
  36 #include <linux/mount.h>
  37 #include <linux/kernel.h>
  38 #include <linux/init.h>
  39 #include <asm/uaccess.h>
  40
  41 extern int max_threads;
  42
  43 static struct workqueue_struct *khelper_wq;
  44
  45 #ifdef CONFIG_KMOD
  46
  47 /*
  48         modprobe_path is set via /proc/sys.
  49 */
  50 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  51
  52 /**
  53  * request_module - try to load a kernel module
  54  * @fmt:     printf style format string for the name of the module
  55  * @varargs: arguements as specified in the format string
  56  *
  57  * Load a module using the user mode module loader. The function returns
  58  * zero on success or a negative errno code on failure. Note that a
  59  * successful module load does not mean the module did not then unload
  60  * and exit on an error of its own. Callers must check that the service
  61  * they requested is now available not blindly invoke it.
  62  *
  63  * If module auto-loading support is disabled then this function
  64  * becomes a no-operation.
  65  */
  66 int request_module(const char *fmt, ...)
  67 {
  68         va_list args;
  69         char module_name[MODULE_NAME_LEN];
  70         unsigned int max_modprobes;
  71         int ret;
  72         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  73         static char *envp[] = { "HOME=/",
  74                                 "TERM=linux",
  75                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  76                                 NULL };
  77         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  78 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  79         static int kmod_loop_msg;
  80
  81         va_start(args, fmt);
  82         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  83         va_end(args);
  84         if (ret >= MODULE_NAME_LEN)
  85                 return -ENAMETOOLONG;
  86
  87         /* If modprobe needs a service that is in a module, we get a recursive
  88          * loop.  Limit the number of running kmod threads to max_threads/2 or
  89          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  90          * would be to run the parents of this process, counting how many times
  91          * kmod was invoked.  That would mean accessing the internals of the
  92          * process tables to get the command line, proc_pid_cmdline is static
  93          * and it is not worth changing the proc code just to handle this case.
  94          * KAO.
  95          *
  96          * "trace the ppid" is simple, but will fail if someone's
  97          * parent exits.  I think this is as good as it gets. --RR
  98          */
  99         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 100         atomic_inc(&kmod_concurrent);
 101         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 102                 /* We may be blaming an innocent here, but unlikely */
 103                 if (kmod_loop_msg++ < 5)
 104                         printk(KERN_ERR
 105                                "request_module: runaway loop modprobe %s\n",
 106                                module_name);
 107                 atomic_dec(&kmod_concurrent);
 108                 return -ENOMEM;
 109         }
 110
 111         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 112         atomic_dec(&kmod_concurrent);
 113         return ret;
 114 }
 115 EXPORT_SYMBOL(request_module);
 116 #endif /* CONFIG_KMOD */
 117
 118 #ifdef CONFIG_HOTPLUG
 119 /*
 120         hotplug path is set via /proc/sys
 121         invoked by hotplug-aware bus drivers,
 122         with call_usermodehelper
 123
 124         argv [0] = hotplug_path;
 125         argv [1] = "usb", "scsi", "pci", "network", etc;
 126         ... plus optional type-specific parameters
 127         argv [n] = 0;
 128
 129         envp [*] = HOME, PATH; optional type-specific parameters
 130
 131         a hotplug bus should invoke this for device add/remove
 132         events.  the command is expected to load drivers when
 133         necessary, and may perform additional system setup.
 134 */
 135 char hotplug_path[KMOD_PATH_LEN] = "/sbin/hotplug";
 136
 137 EXPORT_SYMBOL(hotplug_path);
 138
 139 #endif /* CONFIG_HOTPLUG */
 140
 141 struct subprocess_info {
 142         struct completion *complete;
 143         char *path;
 144         char **argv;
 145         char **envp;
 146         int wait;
 147         int retval;
 148 };
 149
 150 /*
 151  * This is the task which runs the usermode application
 152  */
 153 static int ____call_usermodehelper(void *data)
 154 {
 155         struct subprocess_info *sub_info = data;
 156         int retval;
 157
 158         /* Unblock all signals. */
 159         flush_signals(current);
 160         spin_lock_irq(&current->sighand->siglock);
 161         flush_signal_handlers(current, 1);
 162         sigemptyset(&current->blocked);
 163         recalc_sigpending();
 164         spin_unlock_irq(&current->sighand->siglock);
 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 = execve(sub_info->path, 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, (struct k_sigaction *)0);
 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                 /*
 198                  * Normally it is bogus to call wait4() from in-kernel because
 199                  * wait4() wants to write the exit code to a userspace address.
 200                  * But wait_for_helper() always runs as keventd, and put_user()
 201                  * to a kernel address works OK for kernel threads, due to their
 202                  * having an mm_segment_t which spans the entire address space.
 203                  *
 204                  * Thus the __user pointer cast is valid here.
 205                  */
 206                 sys_wait4(pid, (int __user *) &sub_info->retval, 0, NULL);
 207         }
 208
 209         complete(sub_info->complete);
 210         return 0;
 211 }
 212
 213 /* This is run by khelper thread  */
 214 static void __call_usermodehelper(void *data)
 215 {
 216         struct subprocess_info *sub_info = data;
 217         pid_t pid;
 218
 219         /* CLONE_VFORK: wait until the usermode helper has execve'd
 220          * successfully We need the data structures to stay around
 221          * until that is done.  */
 222         if (sub_info->wait)
 223                 pid = kernel_thread(wait_for_helper, sub_info,
 224                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 225         else
 226                 pid = kernel_thread(____call_usermodehelper, sub_info,
 227                                     CLONE_VFORK | SIGCHLD);
 228
 229         if (pid < 0) {
 230                 sub_info->retval = pid;
 231                 complete(sub_info->complete);
 232         } else if (!sub_info->wait)
 233                 complete(sub_info->complete);
 234 }
 235
 236 /**
 237  * call_usermodehelper - start a usermode application
 238  * @path: pathname for the application
 239  * @argv: null-terminated argument list
 240  * @envp: null-terminated environment list
 241  * @wait: wait for the application to finish and return status.
 242  *
 243  * Runs a user-space application.  The application is started
 244  * asynchronously if wait is not set, and runs as a child of keventd.
 245  * (ie. it runs with full root capabilities).
 246  *
 247  * Must be called from process context.  Returns a negative error code
 248  * if program was not execed successfully, or 0.
 249  */
 250 int call_usermodehelper(char *path, char **argv, char **envp, int wait)
 251 {
 252         DECLARE_COMPLETION(done);
 253         struct subprocess_info sub_info = {
 254                 .complete       = &done,
 255                 .path           = path,
 256                 .argv           = argv,
 257                 .envp           = envp,
 258                 .wait           = wait,
 259                 .retval         = 0,
 260         };
 261         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 262
 263         if (!khelper_wq)
 264                 return -EBUSY;
 265
 266         if (path[0] == '\0')
 267                 return 0;
 268
 269         queue_work(khelper_wq, &work);
 270         wait_for_completion(&done);
 271         return sub_info.retval;
 272 }
 273 EXPORT_SYMBOL(call_usermodehelper);
 274
 275 void __init usermodehelper_init(void)
 276 {
 277         khelper_wq = create_singlethread_workqueue("khelper");
 278         BUG_ON(!khelper_wq);
 279 }