src/udev/udev-node.c

   1 /* SPDX-License-Identifier: GPL-2.0+ */
   2 /*
   3  * Copyright (C) 2003-2013 Kay Sievers <kay@vrfy.org>
   4  *
   5  * This program is free software: you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation, either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <stdbool.h>
  22 #include <stddef.h>
  23 #include <stdio.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <unistd.h>
  27
  28 #include "device-nodes.h"
  29 #include "dirent-util.h"
  30 #include "format-util.h"
  31 #include "fs-util.h"
  32 #include "selinux-util.h"
  33 #include "smack-util.h"
  34 #include "stdio-util.h"
  35 #include "string-util.h"
  36 #include "udev.h"
  37
  38 static int node_symlink(struct udev_device *dev, const char *node, const char *slink) {
  39         struct stat stats;
  40         char target[UTIL_PATH_SIZE];
  41         char *s;
  42         size_t l;
  43         char slink_tmp[UTIL_PATH_SIZE + 32];
  44         int i = 0;
  45         int tail = 0;
  46         int err = 0;
  47
  48         /* use relative link */
  49         target[0] = '\0';
  50         while (node[i] && (node[i] == slink[i])) {
  51                 if (node[i] == '/')
  52                         tail = i+1;
  53                 i++;
  54         }
  55         s = target;
  56         l = sizeof(target);
  57         while (slink[i] != '\0') {
  58                 if (slink[i] == '/')
  59                         l = strpcpy(&s, l, "../");
  60                 i++;
  61         }
  62         l = strscpy(s, l, &node[tail]);
  63         if (l == 0) {
  64                 err = -EINVAL;
  65                 goto exit;
  66         }
  67
  68         /* preserve link with correct target, do not replace node of other device */
  69         if (lstat(slink, &stats) == 0) {
  70                 if (S_ISBLK(stats.st_mode) || S_ISCHR(stats.st_mode)) {
  71                         log_error("conflicting device node '%s' found, link to '%s' will not be created", slink, node);
  72                         goto exit;
  73                 } else if (S_ISLNK(stats.st_mode)) {
  74                         char buf[UTIL_PATH_SIZE];
  75                         int len;
  76
  77                         len = readlink(slink, buf, sizeof(buf));
  78                         if (len > 0 && len < (int)sizeof(buf)) {
  79                                 buf[len] = '\0';
  80                                 if (streq(target, buf)) {
  81                                         log_debug("preserve already existing symlink '%s' to '%s'", slink, target);
  82                                         label_fix(slink, true, false);
  83                                         utimensat(AT_FDCWD, slink, NULL, AT_SYMLINK_NOFOLLOW);
  84                                         goto exit;
  85                                 }
  86                         }
  87                 }
  88         } else {
  89                 log_debug("creating symlink '%s' to '%s'", slink, target);
  90                 do {
  91                         err = mkdir_parents_label(slink, 0755);
  92                         if (!IN_SET(err, 0, -ENOENT))
  93                                 break;
  94                         mac_selinux_create_file_prepare(slink, S_IFLNK);
  95                         err = symlink(target, slink);
  96                         if (err != 0)
  97                                 err = -errno;
  98                         mac_selinux_create_file_clear();
  99                 } while (err == -ENOENT);
 100                 if (err == 0)
 101                         goto exit;
 102         }
 103
 104         log_debug("atomically replace '%s'", slink);
 105         strscpyl(slink_tmp, sizeof(slink_tmp), slink, ".tmp-", udev_device_get_id_filename(dev), NULL);
 106         unlink(slink_tmp);
 107         do {
 108                 err = mkdir_parents_label(slink_tmp, 0755);
 109                 if (!IN_SET(err, 0, -ENOENT))
 110                         break;
 111                 mac_selinux_create_file_prepare(slink_tmp, S_IFLNK);
 112                 err = symlink(target, slink_tmp);
 113                 if (err != 0)
 114                         err = -errno;
 115                 mac_selinux_create_file_clear();
 116         } while (err == -ENOENT);
 117         if (err != 0) {
 118                 log_error_errno(errno, "symlink '%s' '%s' failed: %m", target, slink_tmp);
 119                 goto exit;
 120         }
 121         err = rename(slink_tmp, slink);
 122         if (err != 0) {
 123                 log_error_errno(errno, "rename '%s' '%s' failed: %m", slink_tmp, slink);
 124                 unlink(slink_tmp);
 125         }
 126 exit:
 127         return err;
 128 }
 129
 130 /* find device node of device with highest priority */
 131 static const char *link_find_prioritized(struct udev_device *dev, bool add, const char *stackdir, char *buf, size_t bufsize) {
 132         struct udev *udev = udev_device_get_udev(dev);
 133         DIR *dir;
 134         struct dirent *dent;
 135         int priority = 0;
 136         const char *target = NULL;
 137
 138         if (add) {
 139                 priority = udev_device_get_devlink_priority(dev);
 140                 strscpy(buf, bufsize, udev_device_get_devnode(dev));
 141                 target = buf;
 142         }
 143
 144         dir = opendir(stackdir);
 145         if (dir == NULL)
 146                 return target;
 147         FOREACH_DIRENT_ALL(dent, dir, break) {
 148                 struct udev_device *dev_db;
 149
 150                 if (dent->d_name[0] == '\0')
 151                         break;
 152                 if (dent->d_name[0] == '.')
 153                         continue;
 154
 155                 log_debug("found '%s' claiming '%s'", dent->d_name, stackdir);
 156
 157                 /* did we find ourself? */
 158                 if (streq(dent->d_name, udev_device_get_id_filename(dev)))
 159                         continue;
 160
 161                 dev_db = udev_device_new_from_device_id(udev, dent->d_name);
 162                 if (dev_db != NULL) {
 163                         const char *devnode;
 164
 165                         devnode = udev_device_get_devnode(dev_db);
 166                         if (devnode != NULL) {
 167                                 if (target == NULL || udev_device_get_devlink_priority(dev_db) > priority) {
 168                                         log_debug("'%s' claims priority %i for '%s'",
 169                                                   udev_device_get_syspath(dev_db), udev_device_get_devlink_priority(dev_db), stackdir);
 170                                         priority = udev_device_get_devlink_priority(dev_db);
 171                                         strscpy(buf, bufsize, devnode);
 172                                         target = buf;
 173                                 }
 174                         }
 175                         udev_device_unref(dev_db);
 176                 }
 177         }
 178         closedir(dir);
 179         return target;
 180 }
 181
 182 /* manage "stack of names" with possibly specified device priorities */
 183 static void link_update(struct udev_device *dev, const char *slink, bool add) {
 184         char name_enc[UTIL_PATH_SIZE];
 185         char filename[UTIL_PATH_SIZE * 2];
 186         char dirname[UTIL_PATH_SIZE];
 187         const char *target;
 188         char buf[UTIL_PATH_SIZE];
 189
 190         util_path_encode(slink + strlen("/dev"), name_enc, sizeof(name_enc));
 191         strscpyl(dirname, sizeof(dirname), "/run/udev/links/", name_enc, NULL);
 192         strscpyl(filename, sizeof(filename), dirname, "/", udev_device_get_id_filename(dev), NULL);
 193
 194         if (!add && unlink(filename) == 0)
 195                 rmdir(dirname);
 196
 197         target = link_find_prioritized(dev, add, dirname, buf, sizeof(buf));
 198         if (target == NULL) {
 199                 log_debug("no reference left, remove '%s'", slink);
 200                 if (unlink(slink) == 0)
 201                         rmdir_parents(slink, "/");
 202         } else {
 203                 log_debug("creating link '%s' to '%s'", slink, target);
 204                 node_symlink(dev, target, slink);
 205         }
 206
 207         if (add) {
 208                 int err;
 209
 210                 do {
 211                         int fd;
 212
 213                         err = mkdir_parents(filename, 0755);
 214                         if (!IN_SET(err, 0, -ENOENT))
 215                                 break;
 216                         fd = open(filename, O_WRONLY|O_CREAT|O_CLOEXEC|O_TRUNC|O_NOFOLLOW, 0444);
 217                         if (fd >= 0)
 218                                 close(fd);
 219                         else
 220                                 err = -errno;
 221                 } while (err == -ENOENT);
 222         }
 223 }
 224
 225 void udev_node_update_old_links(struct udev_device *dev, struct udev_device *dev_old) {
 226         struct udev_list_entry *list_entry;
 227
 228         /* update possible left-over symlinks */
 229         udev_list_entry_foreach(list_entry, udev_device_get_devlinks_list_entry(dev_old)) {
 230                 const char *name = udev_list_entry_get_name(list_entry);
 231                 struct udev_list_entry *list_entry_current;
 232                 int found;
 233
 234                 /* check if old link name still belongs to this device */
 235                 found = 0;
 236                 udev_list_entry_foreach(list_entry_current, udev_device_get_devlinks_list_entry(dev)) {
 237                         const char *name_current = udev_list_entry_get_name(list_entry_current);
 238
 239                         if (streq(name, name_current)) {
 240                                 found = 1;
 241                                 break;
 242                         }
 243                 }
 244                 if (found)
 245                         continue;
 246
 247                 log_debug("update old name, '%s' no longer belonging to '%s'",
 248                      name, udev_device_get_devpath(dev));
 249                 link_update(dev, name, false);
 250         }
 251 }
 252
 253 static int node_permissions_apply(struct udev_device *dev, bool apply,
 254                                   mode_t mode, uid_t uid, gid_t gid,
 255                                   struct udev_list *seclabel_list) {
 256         const char *devnode = udev_device_get_devnode(dev);
 257         dev_t devnum = udev_device_get_devnum(dev);
 258         struct stat stats;
 259         struct udev_list_entry *entry;
 260         int err = 0;
 261
 262         if (streq(udev_device_get_subsystem(dev), "block"))
 263                 mode |= S_IFBLK;
 264         else
 265                 mode |= S_IFCHR;
 266
 267         if (lstat(devnode, &stats) != 0) {
 268                 err = log_debug_errno(errno, "can not stat() node '%s' (%m)", devnode);
 269                 goto out;
 270         }
 271
 272         if (((stats.st_mode & S_IFMT) != (mode & S_IFMT)) || (stats.st_rdev != devnum)) {
 273                 err = -EEXIST;
 274                 log_debug("found node '%s' with non-matching devnum %s, skip handling",
 275                           udev_device_get_devnode(dev), udev_device_get_id_filename(dev));
 276                 goto out;
 277         }
 278
 279         if (apply) {
 280                 bool selinux = false;
 281                 bool smack = false;
 282
 283                 if ((stats.st_mode & 0777) != (mode & 0777) || stats.st_uid != uid || stats.st_gid != gid) {
 284                         log_debug("set permissions %s, %#o, uid=%u, gid=%u", devnode, mode, uid, gid);
 285                         err = chmod(devnode, mode);
 286                         if (err < 0)
 287                                 log_warning_errno(errno, "setting mode of %s to %#o failed: %m", devnode, mode);
 288                         err = chown(devnode, uid, gid);
 289                         if (err < 0)
 290                                 log_warning_errno(errno, "setting owner of %s to uid=%u, gid=%u failed: %m", devnode, uid, gid);
 291                 } else {
 292                         log_debug("preserve permissions %s, %#o, uid=%u, gid=%u", devnode, mode, uid, gid);
 293                 }
 294
 295                 /* apply SECLABEL{$module}=$label */
 296                 udev_list_entry_foreach(entry, udev_list_get_entry(seclabel_list)) {
 297                         const char *name, *label;
 298                         int r;
 299
 300                         name = udev_list_entry_get_name(entry);
 301                         label = udev_list_entry_get_value(entry);
 302
 303                         if (streq(name, "selinux")) {
 304                                 selinux = true;
 305
 306                                 r = mac_selinux_apply(devnode, label);
 307                                 if (r < 0)
 308                                         log_error_errno(r, "SECLABEL: failed to set SELinux label '%s': %m", label);
 309                                 else
 310                                         log_debug("SECLABEL: set SELinux label '%s'", label);
 311
 312                         } else if (streq(name, "smack")) {
 313                                 smack = true;
 314
 315                                 r = mac_smack_apply(devnode, SMACK_ATTR_ACCESS, label);
 316                                 if (r < 0)
 317                                         log_error_errno(r, "SECLABEL: failed to set SMACK label '%s': %m", label);
 318                                 else
 319                                         log_debug("SECLABEL: set SMACK label '%s'", label);
 320
 321                         } else
 322                                 log_error("SECLABEL: unknown subsystem, ignoring '%s'='%s'", name, label);
 323                 }
 324
 325                 /* set the defaults */
 326                 if (!selinux)
 327                         mac_selinux_fix(devnode, true, false);
 328                 if (!smack)
 329                         mac_smack_apply(devnode, SMACK_ATTR_ACCESS, NULL);
 330         }
 331
 332         /* always update timestamp when we re-use the node, like on media change events */
 333         utimensat(AT_FDCWD, devnode, NULL, 0);
 334 out:
 335         return err;
 336 }
 337
 338 void udev_node_add(struct udev_device *dev, bool apply,
 339                    mode_t mode, uid_t uid, gid_t gid,
 340                    struct udev_list *seclabel_list) {
 341         char filename[DEV_NUM_PATH_MAX];
 342         struct udev_list_entry *list_entry;
 343
 344         log_debug("handling device node '%s', devnum=%s, mode=%#o, uid="UID_FMT", gid="GID_FMT,
 345                   udev_device_get_devnode(dev), udev_device_get_id_filename(dev), mode, uid, gid);
 346
 347         if (node_permissions_apply(dev, apply, mode, uid, gid, seclabel_list) < 0)
 348                 return;
 349
 350         /* always add /dev/{block,char}/$major:$minor */
 351         xsprintf_dev_num_path(filename,
 352                               streq(udev_device_get_subsystem(dev), "block") ? "block" : "char",
 353                               udev_device_get_devnum(dev));
 354         node_symlink(dev, udev_device_get_devnode(dev), filename);
 355
 356         /* create/update symlinks, add symlinks to name index */
 357         udev_list_entry_foreach(list_entry, udev_device_get_devlinks_list_entry(dev))
 358                         link_update(dev, udev_list_entry_get_name(list_entry), true);
 359 }
 360
 361 void udev_node_remove(struct udev_device *dev) {
 362         struct udev_list_entry *list_entry;
 363         char filename[DEV_NUM_PATH_MAX];
 364
 365         /* remove/update symlinks, remove symlinks from name index */
 366         udev_list_entry_foreach(list_entry, udev_device_get_devlinks_list_entry(dev))
 367                 link_update(dev, udev_list_entry_get_name(list_entry), false);
 368
 369         /* remove /dev/{block,char}/$major:$minor */
 370         xsprintf_dev_num_path(filename,
 371                               streq(udev_device_get_subsystem(dev), "block") ? "block" : "char",
 372                               udev_device_get_devnum(dev));
 373         unlink(filename);
 374 }