drivers/base/devtmpfs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * devtmpfs - kernel-maintained tmpfs-based /dev
   4  *
   5  * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
   6  *
   7  * During bootup, before any driver core device is registered,
   8  * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
   9  * device which requests a device node, will add a node in this
  10  * filesystem.
  11  * By default, all devices are named after the name of the device,
  12  * owned by root and have a default mode of 0600. Subsystems can
  13  * overwrite the default setting if needed.
  14  */
  15
  16 #include <linux/kernel.h>
  17 #include <linux/syscalls.h>
  18 #include <linux/mount.h>
  19 #include <linux/device.h>
  20 #include <linux/genhd.h>
  21 #include <linux/namei.h>
  22 #include <linux/fs.h>
  23 #include <linux/shmem_fs.h>
  24 #include <linux/ramfs.h>
  25 #include <linux/sched.h>
  26 #include <linux/slab.h>
  27 #include <linux/kthread.h>
  28 #include "base.h"
  29
  30 static struct task_struct *thread;
  31
  32 #if defined CONFIG_DEVTMPFS_MOUNT
  33 static int mount_dev = 1;
  34 #else
  35 static int mount_dev;
  36 #endif
  37
  38 static DEFINE_SPINLOCK(req_lock);
  39
  40 static struct req {
  41         struct req *next;
  42         struct completion done;
  43         int err;
  44         const char *name;
  45         umode_t mode;   /* 0 => delete */
  46         kuid_t uid;
  47         kgid_t gid;
  48         struct device *dev;
  49 } *requests;
  50
  51 static int __init mount_param(char *str)
  52 {
  53         mount_dev = simple_strtoul(str, NULL, 0);
  54         return 1;
  55 }
  56 __setup("devtmpfs.mount=", mount_param);
  57
  58 static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
  59                       const char *dev_name, void *data)
  60 {
  61 #ifdef CONFIG_TMPFS
  62         return mount_single(fs_type, flags, data, shmem_fill_super);
  63 #else
  64         return mount_single(fs_type, flags, data, ramfs_fill_super);
  65 #endif
  66 }
  67
  68 static struct file_system_type dev_fs_type = {
  69         .name = "devtmpfs",
  70         .mount = dev_mount,
  71         .kill_sb = kill_litter_super,
  72 };
  73
  74 #ifdef CONFIG_BLOCK
  75 static inline int is_blockdev(struct device *dev)
  76 {
  77         return dev->class == &block_class;
  78 }
  79 #else
  80 static inline int is_blockdev(struct device *dev) { return 0; }
  81 #endif
  82
  83 int devtmpfs_create_node(struct device *dev)
  84 {
  85         const char *tmp = NULL;
  86         struct req req;
  87
  88         if (!thread)
  89                 return 0;
  90
  91         req.mode = 0;
  92         req.uid = GLOBAL_ROOT_UID;
  93         req.gid = GLOBAL_ROOT_GID;
  94         req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
  95         if (!req.name)
  96                 return -ENOMEM;
  97
  98         if (req.mode == 0)
  99                 req.mode = 0600;
 100         if (is_blockdev(dev))
 101                 req.mode |= S_IFBLK;
 102         else
 103                 req.mode |= S_IFCHR;
 104
 105         req.dev = dev;
 106
 107         init_completion(&req.done);
 108
 109         spin_lock(&req_lock);
 110         req.next = requests;
 111         requests = &req;
 112         spin_unlock(&req_lock);
 113
 114         wake_up_process(thread);
 115         wait_for_completion(&req.done);
 116
 117         kfree(tmp);
 118
 119         return req.err;
 120 }
 121
 122 int devtmpfs_delete_node(struct device *dev)
 123 {
 124         const char *tmp = NULL;
 125         struct req req;
 126
 127         if (!thread)
 128                 return 0;
 129
 130         req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
 131         if (!req.name)
 132                 return -ENOMEM;
 133
 134         req.mode = 0;
 135         req.dev = dev;
 136
 137         init_completion(&req.done);
 138
 139         spin_lock(&req_lock);
 140         req.next = requests;
 141         requests = &req;
 142         spin_unlock(&req_lock);
 143
 144         wake_up_process(thread);
 145         wait_for_completion(&req.done);
 146
 147         kfree(tmp);
 148         return req.err;
 149 }
 150
 151 static int dev_mkdir(const char *name, umode_t mode)
 152 {
 153         struct dentry *dentry;
 154         struct path path;
 155         int err;
 156
 157         dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
 158         if (IS_ERR(dentry))
 159                 return PTR_ERR(dentry);
 160
 161         err = vfs_mkdir(d_inode(path.dentry), dentry, mode);
 162         if (!err)
 163                 /* mark as kernel-created inode */
 164                 d_inode(dentry)->i_private = &thread;
 165         done_path_create(&path, dentry);
 166         return err;
 167 }
 168
 169 static int create_path(const char *nodepath)
 170 {
 171         char *path;
 172         char *s;
 173         int err = 0;
 174
 175         /* parent directories do not exist, create them */
 176         path = kstrdup(nodepath, GFP_KERNEL);
 177         if (!path)
 178                 return -ENOMEM;
 179
 180         s = path;
 181         for (;;) {
 182                 s = strchr(s, '/');
 183                 if (!s)
 184                         break;
 185                 s[0] = '\0';
 186                 err = dev_mkdir(path, 0755);
 187                 if (err && err != -EEXIST)
 188                         break;
 189                 s[0] = '/';
 190                 s++;
 191         }
 192         kfree(path);
 193         return err;
 194 }
 195
 196 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
 197                          kgid_t gid, struct device *dev)
 198 {
 199         struct dentry *dentry;
 200         struct path path;
 201         int err;
 202
 203         dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 204         if (dentry == ERR_PTR(-ENOENT)) {
 205                 create_path(nodename);
 206                 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 207         }
 208         if (IS_ERR(dentry))
 209                 return PTR_ERR(dentry);
 210
 211         err = vfs_mknod(d_inode(path.dentry), dentry, mode, dev->devt);
 212         if (!err) {
 213                 struct iattr newattrs;
 214
 215                 newattrs.ia_mode = mode;
 216                 newattrs.ia_uid = uid;
 217                 newattrs.ia_gid = gid;
 218                 newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
 219                 inode_lock(d_inode(dentry));
 220                 notify_change(dentry, &newattrs, NULL);
 221                 inode_unlock(d_inode(dentry));
 222
 223                 /* mark as kernel-created inode */
 224                 d_inode(dentry)->i_private = &thread;
 225         }
 226         done_path_create(&path, dentry);
 227         return err;
 228 }
 229
 230 static int dev_rmdir(const char *name)
 231 {
 232         struct path parent;
 233         struct dentry *dentry;
 234         int err;
 235
 236         dentry = kern_path_locked(name, &parent);
 237         if (IS_ERR(dentry))
 238                 return PTR_ERR(dentry);
 239         if (d_really_is_positive(dentry)) {
 240                 if (d_inode(dentry)->i_private == &thread)
 241                         err = vfs_rmdir(d_inode(parent.dentry), dentry);
 242                 else
 243                         err = -EPERM;
 244         } else {
 245                 err = -ENOENT;
 246         }
 247         dput(dentry);
 248         inode_unlock(d_inode(parent.dentry));
 249         path_put(&parent);
 250         return err;
 251 }
 252
 253 static int delete_path(const char *nodepath)
 254 {
 255         const char *path;
 256         int err = 0;
 257
 258         path = kstrdup(nodepath, GFP_KERNEL);
 259         if (!path)
 260                 return -ENOMEM;
 261
 262         for (;;) {
 263                 char *base;
 264
 265                 base = strrchr(path, '/');
 266                 if (!base)
 267                         break;
 268                 base[0] = '\0';
 269                 err = dev_rmdir(path);
 270                 if (err)
 271                         break;
 272         }
 273
 274         kfree(path);
 275         return err;
 276 }
 277
 278 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 279 {
 280         /* did we create it */
 281         if (inode->i_private != &thread)
 282                 return 0;
 283
 284         /* does the dev_t match */
 285         if (is_blockdev(dev)) {
 286                 if (!S_ISBLK(stat->mode))
 287                         return 0;
 288         } else {
 289                 if (!S_ISCHR(stat->mode))
 290                         return 0;
 291         }
 292         if (stat->rdev != dev->devt)
 293                 return 0;
 294
 295         /* ours */
 296         return 1;
 297 }
 298
 299 static int handle_remove(const char *nodename, struct device *dev)
 300 {
 301         struct path parent;
 302         struct dentry *dentry;
 303         int deleted = 0;
 304         int err;
 305
 306         dentry = kern_path_locked(nodename, &parent);
 307         if (IS_ERR(dentry))
 308                 return PTR_ERR(dentry);
 309
 310         if (d_really_is_positive(dentry)) {
 311                 struct kstat stat;
 312                 struct path p = {.mnt = parent.mnt, .dentry = dentry};
 313                 err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
 314                                   AT_STATX_SYNC_AS_STAT);
 315                 if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
 316                         struct iattr newattrs;
 317                         /*
 318                          * before unlinking this node, reset permissions
 319                          * of possible references like hardlinks
 320                          */
 321                         newattrs.ia_uid = GLOBAL_ROOT_UID;
 322                         newattrs.ia_gid = GLOBAL_ROOT_GID;
 323                         newattrs.ia_mode = stat.mode & ~0777;
 324                         newattrs.ia_valid =
 325                                 ATTR_UID|ATTR_GID|ATTR_MODE;
 326                         inode_lock(d_inode(dentry));
 327                         notify_change(dentry, &newattrs, NULL);
 328                         inode_unlock(d_inode(dentry));
 329                         err = vfs_unlink(d_inode(parent.dentry), dentry, NULL);
 330                         if (!err || err == -ENOENT)
 331                                 deleted = 1;
 332                 }
 333         } else {
 334                 err = -ENOENT;
 335         }
 336         dput(dentry);
 337         inode_unlock(d_inode(parent.dentry));
 338
 339         path_put(&parent);
 340         if (deleted && strchr(nodename, '/'))
 341                 delete_path(nodename);
 342         return err;
 343 }
 344
 345 /*
 346  * If configured, or requested by the commandline, devtmpfs will be
 347  * auto-mounted after the kernel mounted the root filesystem.
 348  */
 349 int devtmpfs_mount(const char *mntdir)
 350 {
 351         int err;
 352
 353         if (!mount_dev)
 354                 return 0;
 355
 356         if (!thread)
 357                 return 0;
 358
 359         err = ksys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT,
 360                          NULL);
 361         if (err)
 362                 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 363         else
 364                 printk(KERN_INFO "devtmpfs: mounted\n");
 365         return err;
 366 }
 367
 368 static DECLARE_COMPLETION(setup_done);
 369
 370 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
 371                   struct device *dev)
 372 {
 373         if (mode)
 374                 return handle_create(name, mode, uid, gid, dev);
 375         else
 376                 return handle_remove(name, dev);
 377 }
 378
 379 static int devtmpfsd(void *p)
 380 {
 381         char options[] = "mode=0755";
 382         int *err = p;
 383         *err = ksys_unshare(CLONE_NEWNS);
 384         if (*err)
 385                 goto out;
 386         *err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
 387         if (*err)
 388                 goto out;
 389         ksys_chdir("/.."); /* will traverse into overmounted root */
 390         ksys_chroot(".");
 391         complete(&setup_done);
 392         while (1) {
 393                 spin_lock(&req_lock);
 394                 while (requests) {
 395                         struct req *req = requests;
 396                         requests = NULL;
 397                         spin_unlock(&req_lock);
 398                         while (req) {
 399                                 struct req *next = req->next;
 400                                 req->err = handle(req->name, req->mode,
 401                                                   req->uid, req->gid, req->dev);
 402                                 complete(&req->done);
 403                                 req = next;
 404                         }
 405                         spin_lock(&req_lock);
 406                 }
 407                 __set_current_state(TASK_INTERRUPTIBLE);
 408                 spin_unlock(&req_lock);
 409                 schedule();
 410         }
 411         return 0;
 412 out:
 413         complete(&setup_done);
 414         return *err;
 415 }
 416
 417 /*
 418  * Create devtmpfs instance, driver-core devices will add their device
 419  * nodes here.
 420  */
 421 int __init devtmpfs_init(void)
 422 {
 423         int err = register_filesystem(&dev_fs_type);
 424         if (err) {
 425                 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 426                        "type %i\n", err);
 427                 return err;
 428         }
 429
 430         thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
 431         if (!IS_ERR(thread)) {
 432                 wait_for_completion(&setup_done);
 433         } else {
 434                 err = PTR_ERR(thread);
 435                 thread = NULL;
 436         }
 437
 438         if (err) {
 439                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 440                 unregister_filesystem(&dev_fs_type);
 441                 return err;
 442         }
 443
 444         printk(KERN_INFO "devtmpfs: initialized\n");
 445         return 0;
 446 }