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 <linux/fs_context.h>
  29 #include <uapi/linux/mount.h>
  30 #include "base.h"
  31
  32 static struct task_struct *thread;
  33
  34 #if defined CONFIG_DEVTMPFS_MOUNT
  35 static int mount_dev = 1;
  36 #else
  37 static int mount_dev;
  38 #endif
  39
  40 static DEFINE_SPINLOCK(req_lock);
  41
  42 static struct req {
  43         struct req *next;
  44         struct completion done;
  45         int err;
  46         const char *name;
  47         umode_t mode;   /* 0 => delete */
  48         kuid_t uid;
  49         kgid_t gid;
  50         struct device *dev;
  51 } *requests;
  52
  53 static int __init mount_param(char *str)
  54 {
  55         mount_dev = simple_strtoul(str, NULL, 0);
  56         return 1;
  57 }
  58 __setup("devtmpfs.mount=", mount_param);
  59
  60 static struct vfsmount *mnt;
  61
  62 static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags,
  63                       const char *dev_name, void *data)
  64 {
  65         struct super_block *s = mnt->mnt_sb;
  66         int err;
  67
  68         atomic_inc(&s->s_active);
  69         down_write(&s->s_umount);
  70         err = reconfigure_single(s, flags, data);
  71         if (err < 0) {
  72                 deactivate_locked_super(s);
  73                 return ERR_PTR(err);
  74         }
  75         return dget(s->s_root);
  76 }
  77
  78 static struct file_system_type internal_fs_type = {
  79         .name = "devtmpfs",
  80 #ifdef CONFIG_TMPFS
  81         .init_fs_context = shmem_init_fs_context,
  82         .parameters     = &shmem_fs_parameters,
  83 #else
  84         .init_fs_context = ramfs_init_fs_context,
  85         .parameters     = &ramfs_fs_parameters,
  86 #endif
  87         .kill_sb = kill_litter_super,
  88 };
  89
  90 static struct file_system_type dev_fs_type = {
  91         .name = "devtmpfs",
  92         .mount = public_dev_mount,
  93 };
  94
  95 #ifdef CONFIG_BLOCK
  96 static inline int is_blockdev(struct device *dev)
  97 {
  98         return dev->class == &block_class;
  99 }
 100 #else
 101 static inline int is_blockdev(struct device *dev) { return 0; }
 102 #endif
 103
 104 int devtmpfs_create_node(struct device *dev)
 105 {
 106         const char *tmp = NULL;
 107         struct req req;
 108
 109         if (!thread)
 110                 return 0;
 111
 112         req.mode = 0;
 113         req.uid = GLOBAL_ROOT_UID;
 114         req.gid = GLOBAL_ROOT_GID;
 115         req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
 116         if (!req.name)
 117                 return -ENOMEM;
 118
 119         if (req.mode == 0)
 120                 req.mode = 0600;
 121         if (is_blockdev(dev))
 122                 req.mode |= S_IFBLK;
 123         else
 124                 req.mode |= S_IFCHR;
 125
 126         req.dev = dev;
 127
 128         init_completion(&req.done);
 129
 130         spin_lock(&req_lock);
 131         req.next = requests;
 132         requests = &req;
 133         spin_unlock(&req_lock);
 134
 135         wake_up_process(thread);
 136         wait_for_completion(&req.done);
 137
 138         kfree(tmp);
 139
 140         return req.err;
 141 }
 142
 143 int devtmpfs_delete_node(struct device *dev)
 144 {
 145         const char *tmp = NULL;
 146         struct req req;
 147
 148         if (!thread)
 149                 return 0;
 150
 151         req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
 152         if (!req.name)
 153                 return -ENOMEM;
 154
 155         req.mode = 0;
 156         req.dev = dev;
 157
 158         init_completion(&req.done);
 159
 160         spin_lock(&req_lock);
 161         req.next = requests;
 162         requests = &req;
 163         spin_unlock(&req_lock);
 164
 165         wake_up_process(thread);
 166         wait_for_completion(&req.done);
 167
 168         kfree(tmp);
 169         return req.err;
 170 }
 171
 172 static int dev_mkdir(const char *name, umode_t mode)
 173 {
 174         struct dentry *dentry;
 175         struct path path;
 176         int err;
 177
 178         dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
 179         if (IS_ERR(dentry))
 180                 return PTR_ERR(dentry);
 181
 182         err = vfs_mkdir(d_inode(path.dentry), dentry, mode);
 183         if (!err)
 184                 /* mark as kernel-created inode */
 185                 d_inode(dentry)->i_private = &thread;
 186         done_path_create(&path, dentry);
 187         return err;
 188 }
 189
 190 static int create_path(const char *nodepath)
 191 {
 192         char *path;
 193         char *s;
 194         int err = 0;
 195
 196         /* parent directories do not exist, create them */
 197         path = kstrdup(nodepath, GFP_KERNEL);
 198         if (!path)
 199                 return -ENOMEM;
 200
 201         s = path;
 202         for (;;) {
 203                 s = strchr(s, '/');
 204                 if (!s)
 205                         break;
 206                 s[0] = '\0';
 207                 err = dev_mkdir(path, 0755);
 208                 if (err && err != -EEXIST)
 209                         break;
 210                 s[0] = '/';
 211                 s++;
 212         }
 213         kfree(path);
 214         return err;
 215 }
 216
 217 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
 218                          kgid_t gid, struct device *dev)
 219 {
 220         struct dentry *dentry;
 221         struct path path;
 222         int err;
 223
 224         dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 225         if (dentry == ERR_PTR(-ENOENT)) {
 226                 create_path(nodename);
 227                 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 228         }
 229         if (IS_ERR(dentry))
 230                 return PTR_ERR(dentry);
 231
 232         err = vfs_mknod(d_inode(path.dentry), dentry, mode, dev->devt);
 233         if (!err) {
 234                 struct iattr newattrs;
 235
 236                 newattrs.ia_mode = mode;
 237                 newattrs.ia_uid = uid;
 238                 newattrs.ia_gid = gid;
 239                 newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
 240                 inode_lock(d_inode(dentry));
 241                 notify_change(dentry, &newattrs, NULL);
 242                 inode_unlock(d_inode(dentry));
 243
 244                 /* mark as kernel-created inode */
 245                 d_inode(dentry)->i_private = &thread;
 246         }
 247         done_path_create(&path, dentry);
 248         return err;
 249 }
 250
 251 static int dev_rmdir(const char *name)
 252 {
 253         struct path parent;
 254         struct dentry *dentry;
 255         int err;
 256
 257         dentry = kern_path_locked(name, &parent);
 258         if (IS_ERR(dentry))
 259                 return PTR_ERR(dentry);
 260         if (d_really_is_positive(dentry)) {
 261                 if (d_inode(dentry)->i_private == &thread)
 262                         err = vfs_rmdir(d_inode(parent.dentry), dentry);
 263                 else
 264                         err = -EPERM;
 265         } else {
 266                 err = -ENOENT;
 267         }
 268         dput(dentry);
 269         inode_unlock(d_inode(parent.dentry));
 270         path_put(&parent);
 271         return err;
 272 }
 273
 274 static int delete_path(const char *nodepath)
 275 {
 276         char *path;
 277         int err = 0;
 278
 279         path = kstrdup(nodepath, GFP_KERNEL);
 280         if (!path)
 281                 return -ENOMEM;
 282
 283         for (;;) {
 284                 char *base;
 285
 286                 base = strrchr(path, '/');
 287                 if (!base)
 288                         break;
 289                 base[0] = '\0';
 290                 err = dev_rmdir(path);
 291                 if (err)
 292                         break;
 293         }
 294
 295         kfree(path);
 296         return err;
 297 }
 298
 299 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 300 {
 301         /* did we create it */
 302         if (inode->i_private != &thread)
 303                 return 0;
 304
 305         /* does the dev_t match */
 306         if (is_blockdev(dev)) {
 307                 if (!S_ISBLK(stat->mode))
 308                         return 0;
 309         } else {
 310                 if (!S_ISCHR(stat->mode))
 311                         return 0;
 312         }
 313         if (stat->rdev != dev->devt)
 314                 return 0;
 315
 316         /* ours */
 317         return 1;
 318 }
 319
 320 static int handle_remove(const char *nodename, struct device *dev)
 321 {
 322         struct path parent;
 323         struct dentry *dentry;
 324         int deleted = 0;
 325         int err;
 326
 327         dentry = kern_path_locked(nodename, &parent);
 328         if (IS_ERR(dentry))
 329                 return PTR_ERR(dentry);
 330
 331         if (d_really_is_positive(dentry)) {
 332                 struct kstat stat;
 333                 struct path p = {.mnt = parent.mnt, .dentry = dentry};
 334                 err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
 335                                   AT_STATX_SYNC_AS_STAT);
 336                 if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
 337                         struct iattr newattrs;
 338                         /*
 339                          * before unlinking this node, reset permissions
 340                          * of possible references like hardlinks
 341                          */
 342                         newattrs.ia_uid = GLOBAL_ROOT_UID;
 343                         newattrs.ia_gid = GLOBAL_ROOT_GID;
 344                         newattrs.ia_mode = stat.mode & ~0777;
 345                         newattrs.ia_valid =
 346                                 ATTR_UID|ATTR_GID|ATTR_MODE;
 347                         inode_lock(d_inode(dentry));
 348                         notify_change(dentry, &newattrs, NULL);
 349                         inode_unlock(d_inode(dentry));
 350                         err = vfs_unlink(d_inode(parent.dentry), dentry, NULL);
 351                         if (!err || err == -ENOENT)
 352                                 deleted = 1;
 353                 }
 354         } else {
 355                 err = -ENOENT;
 356         }
 357         dput(dentry);
 358         inode_unlock(d_inode(parent.dentry));
 359
 360         path_put(&parent);
 361         if (deleted && strchr(nodename, '/'))
 362                 delete_path(nodename);
 363         return err;
 364 }
 365
 366 /*
 367  * If configured, or requested by the commandline, devtmpfs will be
 368  * auto-mounted after the kernel mounted the root filesystem.
 369  */
 370 int devtmpfs_mount(const char *mntdir)
 371 {
 372         int err;
 373
 374         if (!mount_dev)
 375                 return 0;
 376
 377         if (!thread)
 378                 return 0;
 379
 380         err = ksys_mount("devtmpfs", mntdir, "devtmpfs", MS_SILENT, NULL);
 381         if (err)
 382                 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 383         else
 384                 printk(KERN_INFO "devtmpfs: mounted\n");
 385         return err;
 386 }
 387
 388 static DECLARE_COMPLETION(setup_done);
 389
 390 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
 391                   struct device *dev)
 392 {
 393         if (mode)
 394                 return handle_create(name, mode, uid, gid, dev);
 395         else
 396                 return handle_remove(name, dev);
 397 }
 398
 399 static int devtmpfsd(void *p)
 400 {
 401         int *err = p;
 402         *err = ksys_unshare(CLONE_NEWNS);
 403         if (*err)
 404                 goto out;
 405         *err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
 406         if (*err)
 407                 goto out;
 408         ksys_chdir("/.."); /* will traverse into overmounted root */
 409         ksys_chroot(".");
 410         complete(&setup_done);
 411         while (1) {
 412                 spin_lock(&req_lock);
 413                 while (requests) {
 414                         struct req *req = requests;
 415                         requests = NULL;
 416                         spin_unlock(&req_lock);
 417                         while (req) {
 418                                 struct req *next = req->next;
 419                                 req->err = handle(req->name, req->mode,
 420                                                   req->uid, req->gid, req->dev);
 421                                 complete(&req->done);
 422                                 req = next;
 423                         }
 424                         spin_lock(&req_lock);
 425                 }
 426                 __set_current_state(TASK_INTERRUPTIBLE);
 427                 spin_unlock(&req_lock);
 428                 schedule();
 429         }
 430         return 0;
 431 out:
 432         complete(&setup_done);
 433         return *err;
 434 }
 435
 436 /*
 437  * Create devtmpfs instance, driver-core devices will add their device
 438  * nodes here.
 439  */
 440 int __init devtmpfs_init(void)
 441 {
 442         char opts[] = "mode=0755";
 443         int err;
 444
 445         mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
 446         if (IS_ERR(mnt)) {
 447                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %ld\n",
 448                                 PTR_ERR(mnt));
 449                 return PTR_ERR(mnt);
 450         }
 451         err = register_filesystem(&dev_fs_type);
 452         if (err) {
 453                 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 454                        "type %i\n", err);
 455                 return err;
 456         }
 457
 458         thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
 459         if (!IS_ERR(thread)) {
 460                 wait_for_completion(&setup_done);
 461         } else {
 462                 err = PTR_ERR(thread);
 463                 thread = NULL;
 464         }
 465
 466         if (err) {
 467                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 468                 unregister_filesystem(&dev_fs_type);
 469                 return err;
 470         }
 471
 472         printk(KERN_INFO "devtmpfs: initialized\n");
 473         return 0;
 474 }