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, system_running;
  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  * @module_name: Name of module
  51  *
  52  * Load a module using the user mode module loader. The function returns
  53  * zero on success or a negative errno code on failure. Note that a
  54  * successful module load does not mean the module did not then unload
  55  * and exit on an error of its own. Callers must check that the service
  56  * they requested is now available not blindly invoke it.
  57  *
  58  * If module auto-loading support is disabled then this function
  59  * becomes a no-operation.
  60  */
  61 int request_module(const char *fmt, ...)
  62 {
  63 #define MODULENAME_SIZE 32
  64         va_list args;
  65         char module_name[MODULENAME_SIZE];
  66         unsigned int max_modprobes;
  67         int ret;
  68         char *argv[] = { modprobe_path, "--", 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, MODULENAME_SIZE, fmt, args);
  79         va_end(args);
  80         if (ret >= MODULENAME_SIZE)
  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
 186         sub_info->retval = 0;
 187         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 188         if (pid < 0)
 189                 sub_info->retval = pid;
 190         else
 191                 /* We don't have a SIGCHLD signal handler, so this
 192                  * always returns -ECHILD, but the important thing is
 193                  * that it blocks. */
 194                 sys_wait4(pid, NULL, 0, NULL);
 195
 196         complete(sub_info->complete);
 197         return 0;
 198 }
 199
 200 /*
 201  * This is run by keventd.
 202  */
 203 static void __call_usermodehelper(void *data)
 204 {
 205         struct subprocess_info *sub_info = data;
 206         pid_t pid;
 207
 208         /* CLONE_VFORK: wait until the usermode helper has execve'd
 209          * successfully We need the data structures to stay around
 210          * until that is done.  */
 211         if (sub_info->wait)
 212                 pid = kernel_thread(wait_for_helper, sub_info,
 213                                     CLONE_KERNEL | SIGCHLD);
 214         else
 215                 pid = kernel_thread(____call_usermodehelper, sub_info,
 216                                     CLONE_VFORK | SIGCHLD);
 217
 218         if (pid < 0) {
 219                 sub_info->retval = pid;
 220                 complete(sub_info->complete);
 221         } else if (!sub_info->wait)
 222                 complete(sub_info->complete);
 223 }
 224
 225 /**
 226  * call_usermodehelper - start a usermode application
 227  * @path: pathname for the application
 228  * @argv: null-terminated argument list
 229  * @envp: null-terminated environment list
 230  * @wait: wait for the application to finish and return status.
 231  *
 232  * Runs a user-space application.  The application is started
 233  * asynchronously if wait is not set, and runs as a child of keventd.
 234  * (ie. it runs with full root capabilities).
 235  *
 236  * Must be called from process context.  Returns a negative error code
 237  * if program was not execed successfully, or 0.
 238  */
 239 int call_usermodehelper(char *path, char **argv, char **envp, int wait)
 240 {
 241         DECLARE_COMPLETION(done);
 242         struct subprocess_info sub_info = {
 243                 .complete       = &done,
 244                 .path           = path,
 245                 .argv           = argv,
 246                 .envp           = envp,
 247                 .wait           = wait,
 248                 .retval         = 0,
 249         };
 250         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 251
 252         if (!system_running)
 253                 return -EBUSY;
 254
 255         if (path[0] == '\0')
 256                 goto out;
 257
 258         if (current_is_keventd()) {
 259                 /* We can't wait on keventd! */
 260                 __call_usermodehelper(&sub_info);
 261         } else {
 262                 schedule_work(&work);
 263                 wait_for_completion(&done);
 264         }
 265 out:
 266         return sub_info.retval;
 267 }
 268
 269 EXPORT_SYMBOL(call_usermodehelper);
 270
 271 #ifdef CONFIG_KMOD
 272 EXPORT_SYMBOL(request_module);
 273 #endif
 274