src/script.c

   1 /* script.c -- script routines for vlock, the VT locking program for linux
   2  *
   3  * This program is copyright (C) 2007 Frank Benkstein, and is free
   4  * software which is freely distributable under the terms of the
   5  * GNU General Public License version 2, included as the file COPYING in this
   6  * distribution.  It is NOT public domain software, and any
   7  * redistribution not permitted by the GNU General Public License is
   8  * expressly forbidden without prior written permission from
   9  * the author.
  10  *
  11  */
  12
  13 /* Scripts are executables that are run as unprivileged child processes of
  14  * vlock.  They communicate with vlock through stdin and stdout.
  15  *
  16  * When dependencies are retrieved they are launched once for each dependency
  17  * and should print the names of the plugins they depend on on stdout one per
  18  * line.  The dependency requested is given as a single command line argument.
  19  *
  20  * In hook mode the script is called once with "hooks" as a single command line
  21  * argument.  It should not exit until its stdin closes.  The hook that should
  22  * be executed is written to its stdin on a single line.
  23  *
  24  * Currently there is no way for a script to communicate errors or even success
  25  * to vlock.  If it exits it will linger as a zombie until the plugin is
  26  * destroyed.
  27  */
  28
  29 #if !defined(__FreeBSD__) && !defined(_GNU_SOURCE)
  30 #define _GNU_SOURCE
  31 #endif
  32
  33 #include <stdio.h>
  34 #include <string.h>
  35 #include <stdlib.h>
  36 #include <unistd.h>
  37 #include <limits.h>
  38 #include <sys/select.h>
  39 #include <fcntl.h>
  40 #include <signal.h>
  41 #include <errno.h>
  42 #include <sys/time.h>
  43 #include <time.h>
  44
  45 #include <glib.h>
  46 #include <glib-object.h>
  47
  48 #include "process.h"
  49 #include "util.h"
  50
  51 #include "plugin.h"
  52 #include "script.h"
  53
  54 static char *read_dependency(const char *path, const char *dependency_name, GError **error);
  55 static void parse_dependency(char *data, GList **dependency_list);
  56
  57 /* Get the dependency from the script. */
  58 static bool get_dependency(const char *path, const char *dependency_name,
  59     GList **dependency_list, GError **error)
  60 {
  61   GError *tmp_error = NULL;
  62
  63   /* Read the dependency data. */
  64   char *data = read_dependency(path, dependency_name, &tmp_error);
  65
  66   if (data == NULL)  {
  67     if (tmp_error != NULL) {
  68       g_propagate_error(error, tmp_error);
  69       return false;
  70     } else {
  71       /* No data. */
  72       return true;
  73     }
  74   }
  75
  76   /* Parse the dependency data into the list. */
  77   parse_dependency(data, dependency_list);
  78
  79   return true;
  80 }
  81
  82 /* Read the dependency data by starting the script with the name of the
  83  * dependency as a single command line argument.  The script should then print
  84  * the dependencies to its stdout one on per line. */
  85 static char *read_dependency(const char *path, const char *dependency_name, GError **error)
  86 {
  87   GError *tmp_error = NULL;
  88   const char *argv[] = { path, dependency_name, NULL };
  89   struct child_process child = {
  90     .path = path,
  91     .argv = argv,
  92     .stdin_fd = REDIRECT_DEV_NULL,
  93     .stdout_fd = REDIRECT_PIPE,
  94     .stderr_fd = REDIRECT_DEV_NULL,
  95     .function = NULL,
  96   };
  97   /* Timeout is one second. */
  98   struct timeval timeout = {1, 0};
  99   char *data = g_malloc(sizeof *data);
 100   size_t data_length = 0;
 101
 102   if (!create_child(&child, &tmp_error)) {
 103     g_assert(tmp_error != NULL);
 104     g_propagate_error(error, tmp_error);
 105     return NULL;
 106   }
 107
 108   /* Read the dependency from the child.  Reading fails if either the timeout
 109    * elapses or more that LINE_MAX bytes are read. */
 110   for (;;) {
 111     struct timeval t = timeout;
 112     struct timeval t1;
 113     struct timeval t2;
 114     char buffer[LINE_MAX];
 115     ssize_t length;
 116
 117     fd_set read_fds;
 118
 119     FD_ZERO(&read_fds);
 120     FD_SET(child.stdout_fd, &read_fds);
 121
 122     /* t1 is before select. */
 123     (void) gettimeofday(&t1, NULL);
 124
 125     if (select(child.stdout_fd+1, &read_fds, NULL, NULL, &t) != 1) {
 126 timeout:
 127       g_set_error(&tmp_error,
 128           VLOCK_PLUGIN_ERROR,
 129           VLOCK_PLUGIN_ERROR_FAILED,
 130           "reading dependency (%s) data from script %s failed: timeout",
 131           dependency_name,
 132           /* XXX: plugin->name */ path
 133         );
 134       goto error;
 135     }
 136
 137     /* t2 is after select. */
 138     (void) gettimeofday(&t2, NULL);
 139
 140     /* Get the time that during select. */
 141     timersub(&t2, &t1, &t2);
 142
 143     /* This is very unlikely. */
 144     if (timercmp(&t2, &timeout, >))
 145       goto timeout;
 146
 147     /* Reduce the timeout. */
 148     timersub(&timeout, &t2, &timeout);
 149
 150     /* Read dependency data from the script. */
 151     length = read(child.stdout_fd, buffer, sizeof buffer - 1);
 152
 153     /* Did the script close its stdin or exit? */
 154     if (length <= 0)
 155       break;
 156
 157     if (data_length+length+1 > LINE_MAX) {
 158       g_set_error(&tmp_error,
 159           VLOCK_PLUGIN_ERROR,
 160           VLOCK_PLUGIN_ERROR_FAILED,
 161           "reading dependency (%s) data from script %s failed: too much data",
 162           dependency_name,
 163           /* XXX: plugin->name */ path
 164         );
 165       goto error;
 166     }
 167
 168     /* Grow the data string. */
 169     data = g_realloc(data, data_length+length);
 170
 171     /* Append the buffer to the data string. */
 172     strncpy(data+data_length, buffer, length);
 173     data_length += length;
 174   }
 175
 176   /* Terminate the data string. */
 177   data[data_length] = '\0';
 178
 179 error:
 180   /* Close the read end of the pipe. */
 181   (void) close(child.stdout_fd);
 182   /* Kill the script. */
 183   if (!wait_for_death(child.pid, 0, 500000L))
 184     ensure_death(child.pid);
 185
 186   if (tmp_error != NULL) {
 187     g_propagate_error(error, tmp_error);
 188     g_free(data);
 189     data = NULL;
 190   }
 191
 192   return data;
 193 }
 194
 195 static void parse_dependency(char *data, GList **dependency_list)
 196 {
 197   char **dependency_items = g_strsplit_set(data, " \r\n", -1);
 198
 199   for (size_t i = 0; dependency_items[i] != NULL; i++)
 200     *dependency_list = g_list_append(
 201         *dependency_list,
 202         g_strdup(dependency_items[i])
 203     );
 204
 205   g_strfreev(dependency_items);
 206 }
 207
 208 G_DEFINE_TYPE(VlockScript, vlock_script, TYPE_VLOCK_PLUGIN)
 209
 210 #define VLOCK_SCRIPT_GET_PRIVATE(obj) (G_TYPE_INSTANCE_GET_PRIVATE((obj), TYPE_VLOCK_SCRIPT, VlockScriptPrivate))
 211
 212 struct _VlockScriptPrivate
 213 {
 214   /* The path to the script. */
 215   char *path;
 216   /* Was the script launched? */
 217   bool launched;
 218   /* Did the script die? */
 219   bool dead;
 220   /* The pipe file descriptor that is connected to the script's stdin. */
 221   int fd;
 222   /* The PID of the script. */
 223   pid_t pid;
 224 };
 225
 226 /* Initialize plugin to default values. */
 227 static void vlock_script_init(VlockScript *self)
 228 {
 229   VlockPlugin *plugin = VLOCK_PLUGIN(self);
 230
 231   self->priv = VLOCK_SCRIPT_GET_PRIVATE(self);
 232
 233   self->priv->dead = false;
 234   self->priv->launched = false;
 235   self->priv->path = g_strdup_printf("%s/%s", VLOCK_SCRIPT_DIR, plugin->name);
 236 }
 237
 238 static void vlock_script_finalize(GObject *object)
 239 {
 240   VlockScript *self = VLOCK_SCRIPT(object);
 241
 242   g_free(self->priv->path);
 243
 244   if (self->priv->launched) {
 245     /* Close the pipe. */
 246     (void) close(self->priv->fd);
 247
 248     /* Kill the child process. */
 249     if (!wait_for_death(self->priv->pid, 0, 500000L))
 250       ensure_death(self->priv->pid);
 251   }
 252
 253   G_OBJECT_CLASS(vlock_script_parent_class)->finalize(object);
 254 }
 255
 256 static bool vlock_script_open(VlockPlugin *plugin, GError **error)
 257 {
 258   VlockScript *self = VLOCK_SCRIPT(plugin);
 259
 260   /* Get the dependency information.  Whether the script is executable or not
 261    * is also detected here. */
 262   for (size_t i = 0; i < nr_dependencies; i++)
 263     if (!get_dependency(self->priv->path, dependency_names[i], &plugin->dependencies[i], error))
 264       return false;
 265
 266   return true;
 267 }
 268
 269 /* Launch the script creating a new script_context. */
 270 static bool vlock_script_launch(VlockScript *script, GError **error)
 271 {
 272   GError *tmp_error = NULL;
 273   int fd_flags;
 274   const char *argv[] = { script->priv->path, "hooks", NULL };
 275   struct child_process child = {
 276     .path = script->priv->path,
 277     .argv = argv,
 278     .stdin_fd = REDIRECT_PIPE,
 279     .stdout_fd = REDIRECT_DEV_NULL,
 280     .stderr_fd = REDIRECT_DEV_NULL,
 281     .function = NULL,
 282   };
 283
 284   if (!create_child(&child, &tmp_error)) {
 285     g_propagate_error(error, tmp_error);
 286     return false;
 287   }
 288
 289   script->priv->fd = child.stdin_fd;
 290   script->priv->pid = child.pid;
 291
 292   fd_flags = fcntl(script->priv->fd, F_GETFL, &fd_flags);
 293
 294   if (fd_flags != -1) {
 295     fd_flags |= O_NONBLOCK;
 296     (void) fcntl(script->priv->fd, F_SETFL, fd_flags);
 297   }
 298
 299   return true;
 300 }
 301
 302 static bool vlock_script_call_hook(VlockPlugin *plugin, const gchar *hook_name)
 303 {
 304   VlockScript *self = VLOCK_SCRIPT(plugin);
 305   static const char newline = '\n';
 306   ssize_t hook_name_length = strlen(hook_name);
 307   ssize_t length;
 308   struct sigaction act;
 309   struct sigaction oldact;
 310
 311   if (!self->priv->launched) {
 312     /* Launch script. */
 313     self->priv->launched = vlock_script_launch(self, NULL);
 314
 315     if (!self->priv->launched) {
 316       /* Do not retry. */
 317       self->priv->dead = true;
 318       return false;
 319     }
 320   }
 321
 322   if (self->priv->dead)
 323     /* Nothing to do. */
 324     return false;
 325
 326   /* When writing to a pipe when the read end is closed the kernel invariably
 327    * sends SIGPIPE.   Ignore it. */
 328   (void) sigemptyset(&(act.sa_mask));
 329   act.sa_flags = SA_RESTART;
 330   act.sa_handler = SIG_IGN;
 331   (void) sigaction(SIGPIPE, &act, &oldact);
 332
 333   /* Send hook name and a newline through the pipe. */
 334   length = write(self->priv->fd, hook_name, hook_name_length);
 335
 336   if (length > 0)
 337     length += write(self->priv->fd, &newline, sizeof newline);
 338
 339   /* Restore the previous SIGPIPE handler. */
 340   (void) sigaction(SIGPIPE, &oldact, NULL);
 341
 342   /* If write fails the script is considered dead. */
 343   self->priv->dead = (length != hook_name_length + 1);
 344
 345   return !self->priv->dead;
 346 }
 347
 348
 349 /* Initialize script class. */
 350 static void vlock_script_class_init(VlockScriptClass *klass)
 351 {
 352   GObjectClass *gobject_class = G_OBJECT_CLASS(klass);
 353   VlockPluginClass *plugin_class = VLOCK_PLUGIN_CLASS(klass);
 354
 355   g_type_class_add_private(klass, sizeof(VlockScriptPrivate));
 356
 357   /* Virtual methods. */
 358   gobject_class->finalize = vlock_script_finalize;
 359
 360   plugin_class->open = vlock_script_open;
 361   plugin_class->call_hook = vlock_script_call_hook;
 362 }