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         struct key *ring;
 124         int wait;
 125         int retval;
 126 };
 127
 128 /*
 129  * This is the task which runs the usermode application
 130  */
 131 static int ____call_usermodehelper(void *data)
 132 {
 133         struct subprocess_info *sub_info = data;
 134         struct key *new_session, *old_session;
 135         int retval;
 136
 137         /* Unblock all signals and set the session keyring. */
 138         new_session = key_get(sub_info->ring);
 139         flush_signals(current);
 140         spin_lock_irq(&current->sighand->siglock);
 141         old_session = __install_session_keyring(current, new_session);
 142         flush_signal_handlers(current, 1);
 143         sigemptyset(&current->blocked);
 144         recalc_sigpending();
 145         spin_unlock_irq(&current->sighand->siglock);
 146
 147         key_put(old_session);
 148
 149         /* We can run anywhere, unlike our parent keventd(). */
 150         set_cpus_allowed(current, CPU_MASK_ALL);
 151
 152         retval = -EPERM;
 153         if (current->fs->root)
 154                 retval = execve(sub_info->path, sub_info->argv,sub_info->envp);
 155
 156         /* Exec failed? */
 157         sub_info->retval = retval;
 158         do_exit(0);
 159 }
 160
 161 /* Keventd can't block, but this (a child) can. */
 162 static int wait_for_helper(void *data)
 163 {
 164         struct subprocess_info *sub_info = data;
 165         pid_t pid;
 166         struct k_sigaction sa;
 167
 168         /* Install a handler: if SIGCLD isn't handled sys_wait4 won't
 169          * populate the status, but will return -ECHILD. */
 170         sa.sa.sa_handler = SIG_IGN;
 171         sa.sa.sa_flags = 0;
 172         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 173         do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 174         allow_signal(SIGCHLD);
 175
 176         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 177         if (pid < 0) {
 178                 sub_info->retval = pid;
 179         } else {
 180                 /*
 181                  * Normally it is bogus to call wait4() from in-kernel because
 182                  * wait4() wants to write the exit code to a userspace address.
 183                  * But wait_for_helper() always runs as keventd, and put_user()
 184                  * to a kernel address works OK for kernel threads, due to their
 185                  * having an mm_segment_t which spans the entire address space.
 186                  *
 187                  * Thus the __user pointer cast is valid here.
 188                  */
 189                 sys_wait4(pid, (int __user *) &sub_info->retval, 0, NULL);
 190         }
 191
 192         complete(sub_info->complete);
 193         return 0;
 194 }
 195
 196 /* This is run by khelper thread  */
 197 static void __call_usermodehelper(void *data)
 198 {
 199         struct subprocess_info *sub_info = data;
 200         pid_t pid;
 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 (sub_info->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 (!sub_info->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(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 }