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/module.h>
  24 #include <linux/sched.h>
  25 #include <linux/syscalls.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 <linux/init.h>
  38 #include <asm/uaccess.h>
  39
  40 extern int max_threads;
  41
  42 static struct workqueue_struct *khelper_wq;
  43
  44 #ifdef CONFIG_KMOD
  45
  46 /*
  47         modprobe_path is set via /proc/sys.
  48 */
  49 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  50
  51 /**
  52  * request_module - try to load a kernel module
  53  * @fmt:     printf style format string for the name of the module
  54  * @varargs: arguements as specified in the format string
  55  *
  56  * Load a module using the user mode module loader. The function returns
  57  * zero on success or a negative errno code on failure. Note that a
  58  * successful module load does not mean the module did not then unload
  59  * and exit on an error of its own. Callers must check that the service
  60  * they requested is now available not blindly invoke it.
  61  *
  62  * If module auto-loading support is disabled then this function
  63  * becomes a no-operation.
  64  */
  65 int request_module(const char *fmt, ...)
  66 {
  67         va_list args;
  68         char module_name[MODULE_NAME_LEN];
  69         unsigned int max_modprobes;
  70         int ret;
  71         char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
  72         static char *envp[] = { "HOME=/",
  73                                 "TERM=linux",
  74                                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  75                                 NULL };
  76         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
  77 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
  78         static int kmod_loop_msg;
  79
  80         va_start(args, fmt);
  81         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
  82         va_end(args);
  83         if (ret >= MODULE_NAME_LEN)
  84                 return -ENAMETOOLONG;
  85
  86         /* If modprobe needs a service that is in a module, we get a recursive
  87          * loop.  Limit the number of running kmod threads to max_threads/2 or
  88          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
  89          * would be to run the parents of this process, counting how many times
  90          * kmod was invoked.  That would mean accessing the internals of the
  91          * process tables to get the command line, proc_pid_cmdline is static
  92          * and it is not worth changing the proc code just to handle this case.
  93          * KAO.
  94          *
  95          * "trace the ppid" is simple, but will fail if someone's
  96          * parent exits.  I think this is as good as it gets. --RR
  97          */
  98         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
  99         atomic_inc(&kmod_concurrent);
 100         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 101                 /* We may be blaming an innocent here, but unlikely */
 102                 if (kmod_loop_msg++ < 5)
 103                         printk(KERN_ERR
 104                                "request_module: runaway loop modprobe %s\n",
 105                                module_name);
 106                 atomic_dec(&kmod_concurrent);
 107                 return -ENOMEM;
 108         }
 109
 110         ret = call_usermodehelper(modprobe_path, argv, envp, 1);
 111         atomic_dec(&kmod_concurrent);
 112         return ret;
 113 }
 114 EXPORT_SYMBOL(request_module);
 115 #endif /* CONFIG_KMOD */
 116
 117 struct subprocess_info {
 118         struct completion *complete;
 119         char *path;
 120         char **argv;
 121         char **envp;
 122         struct key *ring;
 123         int wait;
 124         int retval;
 125 };
 126
 127 /*
 128  * This is the task which runs the usermode application
 129  */
 130 static int ____call_usermodehelper(void *data)
 131 {
 132         struct subprocess_info *sub_info = data;
 133         struct key *new_session, *old_session;
 134         int retval;
 135
 136         /* Unblock all signals and set the session keyring. */
 137         new_session = key_get(sub_info->ring);
 138         flush_signals(current);
 139         spin_lock_irq(&current->sighand->siglock);
 140         old_session = __install_session_keyring(current, new_session);
 141         flush_signal_handlers(current, 1);
 142         sigemptyset(&current->blocked);
 143         recalc_sigpending();
 144         spin_unlock_irq(&current->sighand->siglock);
 145
 146         key_put(old_session);
 147
 148         /* We can run anywhere, unlike our parent keventd(). */
 149         set_cpus_allowed(current, CPU_MASK_ALL);
 150
 151         retval = -EPERM;
 152         if (current->fs->root)
 153                 retval = execve(sub_info->path, sub_info->argv,sub_info->envp);
 154
 155         /* Exec failed? */
 156         sub_info->retval = retval;
 157         do_exit(0);
 158 }
 159
 160 /* Keventd can't block, but this (a child) can. */
 161 static int wait_for_helper(void *data)
 162 {
 163         struct subprocess_info *sub_info = data;
 164         pid_t pid;
 165         struct k_sigaction sa;
 166
 167         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 168          * populate the status, but will return -ECHILD. */
 169         sa.sa.sa_handler = SIG_IGN;
 170         sa.sa.sa_flags = 0;
 171         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 172         do_sigaction(SIGCHLD, &sa, NULL);
 173         allow_signal(SIGCHLD);
 174
 175         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 176         if (pid < 0) {
 177                 sub_info->retval = pid;
 178         } else {
 179                 /*
 180                  * Normally it is bogus to call wait4() from in-kernel because
 181                  * wait4() wants to write the exit code to a userspace address.
 182                  * But wait_for_helper() always runs as keventd, and put_user()
 183                  * to a kernel address works OK for kernel threads, due to their
 184                  * having an mm_segment_t which spans the entire address space.
 185                  *
 186                  * Thus the __user pointer cast is valid here.
 187                  */
 188                 sys_wait4(pid, (int __user *) &sub_info->retval, 0, NULL);
 189         }
 190
 191         complete(sub_info->complete);
 192         return 0;
 193 }
 194
 195 /* This is run by khelper thread  */
 196 static void __call_usermodehelper(void *data)
 197 {
 198         struct subprocess_info *sub_info = data;
 199         pid_t pid;
 200         int wait = sub_info->wait;
 201
 202         /* CLONE_VFORK: wait until the usermode helper has execve'd
 203          * successfully We need the data structures to stay around
 204          * until that is done.  */
 205         if (wait)
 206                 pid = kernel_thread(wait_for_helper, sub_info,
 207                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 208         else
 209                 pid = kernel_thread(____call_usermodehelper, sub_info,
 210                                     CLONE_VFORK | SIGCHLD);
 211
 212         if (pid < 0) {
 213                 sub_info->retval = pid;
 214                 complete(sub_info->complete);
 215         } else if (!wait)
 216                 complete(sub_info->complete);
 217 }
 218
 219 /**
 220  * call_usermodehelper_keys - start a usermode application
 221  * @path: pathname for the application
 222  * @argv: null-terminated argument list
 223  * @envp: null-terminated environment list
 224  * @session_keyring: session keyring for process (NULL for an empty keyring)
 225  * @wait: wait for the application to finish and return status.
 226  *
 227  * Runs a user-space application.  The application is started
 228  * asynchronously if wait is not set, and runs as a child of keventd.
 229  * (ie. it runs with full root capabilities).
 230  *
 231  * Must be called from process context.  Returns a negative error code
 232  * if program was not execed successfully, or 0.
 233  */
 234 int call_usermodehelper_keys(char *path, char **argv, char **envp,
 235                              struct key *session_keyring, int wait)
 236 {
 237         DECLARE_COMPLETION_ONSTACK(done);
 238         struct subprocess_info sub_info = {
 239                 .complete       = &done,
 240                 .path           = path,
 241                 .argv           = argv,
 242                 .envp           = envp,
 243                 .ring           = session_keyring,
 244                 .wait           = wait,
 245                 .retval         = 0,
 246         };
 247         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 248
 249         if (!khelper_wq)
 250                 return -EBUSY;
 251
 252         if (path[0] == '\0')
 253                 return 0;
 254
 255         queue_work(khelper_wq, &work);
 256         wait_for_completion(&done);
 257         return sub_info.retval;
 258 }
 259 EXPORT_SYMBOL(call_usermodehelper_keys);
 260
 261 void __init usermodehelper_init(void)
 262 {
 263         khelper_wq = create_singlethread_workqueue("khelper");
 264         BUG_ON(!khelper_wq);
 265 }