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 struct subprocess_info {
 119         struct completion *complete;
 120         char *path;
 121         char **argv;
 122         char **envp;
 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         int retval;
 134
 135         /* Unblock all signals. */
 136         flush_signals(current);
 137         spin_lock_irq(&current->sighand->siglock);
 138         flush_signal_handlers(current, 1);
 139         sigemptyset(&current->blocked);
 140         recalc_sigpending();
 141         spin_unlock_irq(&current->sighand->siglock);
 142
 143         /* We can run anywhere, unlike our parent keventd(). */
 144         set_cpus_allowed(current, CPU_MASK_ALL);
 145
 146         retval = -EPERM;
 147         if (current->fs->root)
 148                 retval = execve(sub_info->path, sub_info->argv,sub_info->envp);
 149
 150         /* Exec failed? */
 151         sub_info->retval = retval;
 152         do_exit(0);
 153 }
 154
 155 /* Keventd can't block, but this (a child) can. */
 156 static int wait_for_helper(void *data)
 157 {
 158         struct subprocess_info *sub_info = data;
 159         pid_t pid;
 160         struct k_sigaction sa;
 161
 162         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 163          * populate the status, but will return -ECHILD. */
 164         sa.sa.sa_handler = SIG_IGN;
 165         sa.sa.sa_flags = 0;
 166         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 167         do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 168         allow_signal(SIGCHLD);
 169
 170         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 171         if (pid < 0) {
 172                 sub_info->retval = pid;
 173         } else {
 174                 /*
 175                  * Normally it is bogus to call wait4() from in-kernel because
 176                  * wait4() wants to write the exit code to a userspace address.
 177                  * But wait_for_helper() always runs as keventd, and put_user()
 178                  * to a kernel address works OK for kernel threads, due to their
 179                  * having an mm_segment_t which spans the entire address space.
 180                  *
 181                  * Thus the __user pointer cast is valid here.
 182                  */
 183                 sys_wait4(pid, (int __user *) &sub_info->retval, 0, NULL);
 184         }
 185
 186         complete(sub_info->complete);
 187         return 0;
 188 }
 189
 190 /* This is run by khelper thread  */
 191 static void __call_usermodehelper(void *data)
 192 {
 193         struct subprocess_info *sub_info = data;
 194         pid_t pid;
 195
 196         /* CLONE_VFORK: wait until the usermode helper has execve'd
 197          * successfully We need the data structures to stay around
 198          * until that is done.  */
 199         if (sub_info->wait)
 200                 pid = kernel_thread(wait_for_helper, sub_info,
 201                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 202         else
 203                 pid = kernel_thread(____call_usermodehelper, sub_info,
 204                                     CLONE_VFORK | SIGCHLD);
 205
 206         if (pid < 0) {
 207                 sub_info->retval = pid;
 208                 complete(sub_info->complete);
 209         } else if (!sub_info->wait)
 210                 complete(sub_info->complete);
 211 }
 212
 213 /**
 214  * call_usermodehelper - start a usermode application
 215  * @path: pathname for the application
 216  * @argv: null-terminated argument list
 217  * @envp: null-terminated environment list
 218  * @wait: wait for the application to finish and return status.
 219  *
 220  * Runs a user-space application.  The application is started
 221  * asynchronously if wait is not set, and runs as a child of keventd.
 222  * (ie. it runs with full root capabilities).
 223  *
 224  * Must be called from process context.  Returns a negative error code
 225  * if program was not execed successfully, or 0.
 226  */
 227 int call_usermodehelper(char *path, char **argv, char **envp, int wait)
 228 {
 229         DECLARE_COMPLETION(done);
 230         struct subprocess_info sub_info = {
 231                 .complete       = &done,
 232                 .path           = path,
 233                 .argv           = argv,
 234                 .envp           = envp,
 235                 .wait           = wait,
 236                 .retval         = 0,
 237         };
 238         DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 239
 240         if (!khelper_wq)
 241                 return -EBUSY;
 242
 243         if (path[0] == '\0')
 244                 return 0;
 245
 246         queue_work(khelper_wq, &work);
 247         wait_for_completion(&done);
 248         return sub_info.retval;
 249 }
 250 EXPORT_SYMBOL(call_usermodehelper);
 251
 252 void __init usermodehelper_init(void)
 253 {
 254         khelper_wq = create_singlethread_workqueue("khelper");
 255         BUG_ON(!khelper_wq);
 256 }