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/unistd.h>
  27 #include <linux/kmod.h>
  28 #include <linux/smp_lock.h>
  29 #include <linux/slab.h>
  30 #include <linux/namespace.h>
  31 #include <linux/completion.h>
  32 #include <linux/file.h>
  33 #include <linux/workqueue.h>
  34 #include <linux/security.h>
  35 #include <linux/mount.h>
  36 #include <linux/kernel.h>
  37 #include <asm/uaccess.h>
  38
  39 extern int max_threads;
  40
  41 #ifdef CONFIG_KMOD
  42
  43 /*
  44         modprobe_path is set via /proc/sys.
  45 */
  46 char modprobe_path[256] = "/sbin/modprobe";
  47
  48 /**
  49  * request_module - try to load a kernel module
  50  * @fmt:     printf style format string for the name of the module
  51  * @varargs: arguements as specified in the format string
  52  *
  53  * Load a module using the user mode module loader. The function returns
  54  * zero on success or a negative errno code on failure. Note that a
  55  * successful module load does not mean the module did not then unload
  56  * and exit on an error of its own. Callers must check that the service
  57  * they requested is now available not blindly invoke it.
  58  *
  59  * If module auto-loading support is disabled then this function
  60  * becomes a no-operation.
  61  */
  62 int request_module(const char *fmt, ...)
  63 {
  64         va_list args;
  65         char module_name[MODULE_NAME_LEN];
  66         unsigned int max_modprobes;
  67         int ret;
  68         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  69         static char *envp[] = { "HOME=/",
  70                                 "TERM=linux",
  71                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  72                                 NULL };
  73         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  74 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  75         static int kmod_loop_msg;
  76
  77         va_start(args, fmt);
  78         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  79         va_end(args);
  80         if (ret >= MODULE_NAME_LEN)
  81                 return -ENAMETOOLONG;
  82
  83         /* If modprobe needs a service that is in a module, we get a recursive
  84          * loop.  Limit the number of running kmod threads to max_threads/2 or
  85          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  86          * would be to run the parents of this process, counting how many times
  87          * kmod was invoked.  That would mean accessing the internals of the
  88          * process tables to get the command line, proc_pid_cmdline is static
  89          * and it is not worth changing the proc code just to handle this case.
  90          * KAO.
  91          *
  92          * "trace the ppid" is simple, but will fail if someone's
  93          * parent exits.  I think this is as good as it gets. --RR
  94          */
  95         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
  96         atomic_inc(&kmod_concurrent);
  97         if (atomic_read(&kmod_concurrent) > max_modprobes) {
  98                 /* We may be blaming an innocent here, but unlikely */
  99                 if (kmod_loop_msg++ < 5)
 100                         printk(KERN_ERR
 101                                "request_module: runaway loop modprobe %s\n",
 102                                module_name);
 103                 atomic_dec(&kmod_concurrent);
 104                 return -ENOMEM;
 105         }
 106
 107         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 108         if (ret != 0) {
 109                 static unsigned long last;
 110                 unsigned long now = jiffies;
 111                 if (now - last > HZ) {
 112                         last = now;
 113                         printk(KERN_DEBUG
 114                                "request_module: failed %s -- %s. error = %d\n",
 115                                modprobe_path, module_name, ret);
 116                 }
 117         }
 118         atomic_dec(&kmod_concurrent);
 119         return ret;
 120 }
 121 #endif /* CONFIG_KMOD */
 122
 123 #ifdef CONFIG_HOTPLUG
 124 /*
 125         hotplug path is set via /proc/sys
 126         invoked by hotplug-aware bus drivers,
 127         with call_usermodehelper
 128
 129         argv [0] = hotplug_path;
 130         argv [1] = "usb", "scsi", "pci", "network", etc;
 131         ... plus optional type-specific parameters
 132         argv [n] = 0;
 133
 134         envp [*] = HOME, PATH; optional type-specific parameters
 135
 136         a hotplug bus should invoke this for device add/remove
 137         events.  the command is expected to load drivers when
 138         necessary, and may perform additional system setup.
 139 */
 140 char hotplug_path[256] = "/sbin/hotplug";
 141
 142 EXPORT_SYMBOL(hotplug_path);
 143
 144 #endif /* CONFIG_HOTPLUG */
 145
 146 struct subprocess_info {
 147         struct completion *complete;
 148         char *path;
 149         char **argv;
 150         char **envp;
 151         int wait;
 152         int retval;
 153 };
 154
 155 /*
 156  * This is the task which runs the usermode application
 157  */
 158 static int ____call_usermodehelper(void *data)
 159 {
 160         struct subprocess_info *sub_info = data;
 161         int retval;
 162
 163         /* Unblock all signals. */
 164         flush_signals(current);
 165         spin_lock_irq(&current->sighand->siglock);
 166         flush_signal_handlers(current, 1);
 167         sigemptyset(&current->blocked);
 168         recalc_sigpending();
 169         spin_unlock_irq(&current->sighand->siglock);
 170
 171         retval = -EPERM;
 172         if (current->fs->root)
 173                 retval = execve(sub_info->path, sub_info->argv,sub_info->envp);
 174
 175         /* Exec failed? */
 176         sub_info->retval = retval;
 177         do_exit(0);
 178 }
 179
 180 /* Keventd can't block, but this (a child) can. */
 181 static int wait_for_helper(void *data)
 182 {
 183         struct subprocess_info *sub_info = data;
 184         pid_t pid;
 185         struct k_sigaction sa;
 186
 187         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 188          * populate the status, but will return -ECHILD. */
 189         sa.sa.sa_handler = SIG_IGN;
 190         sa.sa.sa_flags = 0;
 191         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 192         do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 193         allow_signal(SIGCHLD);
 194
 195         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 196         if (pid < 0)
 197                 sub_info->retval = pid;
 198         else
 199                 sys_wait4(pid, &sub_info->retval, 0, NULL);
 200
 201         complete(sub_info->complete);
 202         return 0;
 203 }
 204
 205 /*
 206  * This is run by keventd.
 207  */
 208 static void __call_usermodehelper(void *data)
 209 {
 210         struct subprocess_info *sub_info = data;
 211         pid_t pid;
 212
 213         /* CLONE_VFORK: wait until the usermode helper has execve'd
 214          * successfully We need the data structures to stay around
 215          * until that is done.  */
 216         if (sub_info->wait)
 217                 pid = kernel_thread(wait_for_helper, sub_info,
 218                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 219         else
 220                 pid = kernel_thread(____call_usermodehelper, sub_info,
 221                                     CLONE_VFORK | SIGCHLD);
 222
 223         if (pid < 0) {
 224                 sub_info->retval = pid;
 225                 complete(sub_info->complete);
 226         } else if (!sub_info->wait)
 227                 complete(sub_info->complete);
 228 }
 229
 230 /**
 231  * call_usermodehelper - start a usermode application
 232  * @path: pathname for the application
 233  * @argv: null-terminated argument list
 234  * @envp: null-terminated environment list
 235  * @wait: wait for the application to finish and return status.
 236  *
 237  * Runs a user-space application.  The application is started
 238  * asynchronously if wait is not set, and runs as a child of keventd.
 239  * (ie. it runs with full root capabilities).
 240  *
 241  * Must be called from process context.  Returns a negative error code
 242  * if program was not execed successfully, or 0.
 243  */
 244 int call_usermodehelper(char *path, char **argv, char **envp, int wait)
 245 {
 246         DECLARE_COMPLETION(done);
 247         struct subprocess_info sub_info = {
 248                 .complete       = &done,
 249                 .path           = path,
 250                 .argv           = argv,
 251                 .envp           = envp,
 252                 .wait           = wait,
 253                 .retval         = 0,
 254         };
 255         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 256
 257         if (!system_running)
 258                 return -EBUSY;
 259
 260         if (path[0] == '\0')
 261                 goto out;
 262
 263         if (current_is_keventd()) {
 264                 /* We can't wait on keventd! */
 265                 __call_usermodehelper(&sub_info);
 266         } else {
 267                 schedule_work(&work);
 268                 wait_for_completion(&done);
 269         }
 270 out:
 271         return sub_info.retval;
 272 }
 273
 274 EXPORT_SYMBOL(call_usermodehelper);
 275
 276 #ifdef CONFIG_KMOD
 277 EXPORT_SYMBOL(request_module);
 278 #endif
 279