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 #define pr_fmt(fmt) "devtmpfs: " fmt
  17
  18 #include <linux/kernel.h>
  19 #include <linux/syscalls.h>
  20 #include <linux/mount.h>
  21 #include <linux/device.h>
  22 #include <linux/blkdev.h>
  23 #include <linux/namei.h>
  24 #include <linux/fs.h>
  25 #include <linux/shmem_fs.h>
  26 #include <linux/ramfs.h>
  27 #include <linux/sched.h>
  28 #include <linux/slab.h>
  29 #include <linux/kthread.h>
  30 #include <linux/init_syscalls.h>
  31 #include <uapi/linux/mount.h>
  32 #include "base.h"
  33
  34 #ifdef CONFIG_DEVTMPFS_SAFE
  35 #define DEVTMPFS_MFLAGS       (MS_SILENT | MS_NOEXEC | MS_NOSUID)
  36 #else
  37 #define DEVTMPFS_MFLAGS       (MS_SILENT)
  38 #endif
  39
  40 static struct task_struct *thread;
  41
  42 static int __initdata mount_dev = IS_ENABLED(CONFIG_DEVTMPFS_MOUNT);
  43
  44 static DEFINE_SPINLOCK(req_lock);
  45
  46 static struct req {
  47         struct req *next;
  48         struct completion done;
  49         int err;
  50         const char *name;
  51         umode_t mode;   /* 0 => delete */
  52         kuid_t uid;
  53         kgid_t gid;
  54         struct device *dev;
  55 } *requests;
  56
  57 static int __init mount_param(char *str)
  58 {
  59         mount_dev = simple_strtoul(str, NULL, 0);
  60         return 1;
  61 }
  62 __setup("devtmpfs.mount=", mount_param);
  63
  64 static struct vfsmount *mnt;
  65
  66 static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags,
  67                       const char *dev_name, void *data)
  68 {
  69         struct super_block *s = mnt->mnt_sb;
  70         int err;
  71
  72         atomic_inc(&s->s_active);
  73         down_write(&s->s_umount);
  74         err = reconfigure_single(s, flags, data);
  75         if (err < 0) {
  76                 deactivate_locked_super(s);
  77                 return ERR_PTR(err);
  78         }
  79         return dget(s->s_root);
  80 }
  81
  82 static struct file_system_type internal_fs_type = {
  83         .name = "devtmpfs",
  84 #ifdef CONFIG_TMPFS
  85         .init_fs_context = shmem_init_fs_context,
  86 #else
  87         .init_fs_context = ramfs_init_fs_context,
  88 #endif
  89         .kill_sb = kill_litter_super,
  90 };
  91
  92 static struct file_system_type dev_fs_type = {
  93         .name = "devtmpfs",
  94         .mount = public_dev_mount,
  95 };
  96
  97 static int devtmpfs_submit_req(struct req *req, const char *tmp)
  98 {
  99         init_completion(&req->done);
 100
 101         spin_lock(&req_lock);
 102         req->next = requests;
 103         requests = req;
 104         spin_unlock(&req_lock);
 105
 106         wake_up_process(thread);
 107         wait_for_completion(&req->done);
 108
 109         kfree(tmp);
 110
 111         return req->err;
 112 }
 113
 114 int devtmpfs_create_node(struct device *dev)
 115 {
 116         const char *tmp = NULL;
 117         struct req req;
 118
 119         if (!thread)
 120                 return 0;
 121
 122         req.mode = 0;
 123         req.uid = GLOBAL_ROOT_UID;
 124         req.gid = GLOBAL_ROOT_GID;
 125         req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
 126         if (!req.name)
 127                 return -ENOMEM;
 128
 129         if (req.mode == 0)
 130                 req.mode = 0600;
 131         if (is_blockdev(dev))
 132                 req.mode |= S_IFBLK;
 133         else
 134                 req.mode |= S_IFCHR;
 135
 136         req.dev = dev;
 137
 138         return devtmpfs_submit_req(&req, tmp);
 139 }
 140
 141 int devtmpfs_delete_node(struct device *dev)
 142 {
 143         const char *tmp = NULL;
 144         struct req req;
 145
 146         if (!thread)
 147                 return 0;
 148
 149         req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
 150         if (!req.name)
 151                 return -ENOMEM;
 152
 153         req.mode = 0;
 154         req.dev = dev;
 155
 156         return devtmpfs_submit_req(&req, tmp);
 157 }
 158
 159 static int dev_mkdir(const char *name, umode_t mode)
 160 {
 161         struct dentry *dentry;
 162         struct path path;
 163         int err;
 164
 165         dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
 166         if (IS_ERR(dentry))
 167                 return PTR_ERR(dentry);
 168
 169         err = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode);
 170         if (!err)
 171                 /* mark as kernel-created inode */
 172                 d_inode(dentry)->i_private = &thread;
 173         done_path_create(&path, dentry);
 174         return err;
 175 }
 176
 177 static int create_path(const char *nodepath)
 178 {
 179         char *path;
 180         char *s;
 181         int err = 0;
 182
 183         /* parent directories do not exist, create them */
 184         path = kstrdup(nodepath, GFP_KERNEL);
 185         if (!path)
 186                 return -ENOMEM;
 187
 188         s = path;
 189         for (;;) {
 190                 s = strchr(s, '/');
 191                 if (!s)
 192                         break;
 193                 s[0] = '\0';
 194                 err = dev_mkdir(path, 0755);
 195                 if (err && err != -EEXIST)
 196                         break;
 197                 s[0] = '/';
 198                 s++;
 199         }
 200         kfree(path);
 201         return err;
 202 }
 203
 204 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
 205                          kgid_t gid, struct device *dev)
 206 {
 207         struct dentry *dentry;
 208         struct path path;
 209         int err;
 210
 211         dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 212         if (dentry == ERR_PTR(-ENOENT)) {
 213                 create_path(nodename);
 214                 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 215         }
 216         if (IS_ERR(dentry))
 217                 return PTR_ERR(dentry);
 218
 219         err = vfs_mknod(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode,
 220                         dev->devt);
 221         if (!err) {
 222                 struct iattr newattrs;
 223
 224                 newattrs.ia_mode = mode;
 225                 newattrs.ia_uid = uid;
 226                 newattrs.ia_gid = gid;
 227                 newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
 228                 inode_lock(d_inode(dentry));
 229                 notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
 230                 inode_unlock(d_inode(dentry));
 231
 232                 /* mark as kernel-created inode */
 233                 d_inode(dentry)->i_private = &thread;
 234         }
 235         done_path_create(&path, dentry);
 236         return err;
 237 }
 238
 239 static int dev_rmdir(const char *name)
 240 {
 241         struct path parent;
 242         struct dentry *dentry;
 243         int err;
 244
 245         dentry = kern_path_locked(name, &parent);
 246         if (IS_ERR(dentry))
 247                 return PTR_ERR(dentry);
 248         if (d_really_is_positive(dentry)) {
 249                 if (d_inode(dentry)->i_private == &thread)
 250                         err = vfs_rmdir(&nop_mnt_idmap, d_inode(parent.dentry),
 251                                         dentry);
 252                 else
 253                         err = -EPERM;
 254         } else {
 255                 err = -ENOENT;
 256         }
 257         dput(dentry);
 258         inode_unlock(d_inode(parent.dentry));
 259         path_put(&parent);
 260         return err;
 261 }
 262
 263 static int delete_path(const char *nodepath)
 264 {
 265         char *path;
 266         int err = 0;
 267
 268         path = kstrdup(nodepath, GFP_KERNEL);
 269         if (!path)
 270                 return -ENOMEM;
 271
 272         for (;;) {
 273                 char *base;
 274
 275                 base = strrchr(path, '/');
 276                 if (!base)
 277                         break;
 278                 base[0] = '\0';
 279                 err = dev_rmdir(path);
 280                 if (err)
 281                         break;
 282         }
 283
 284         kfree(path);
 285         return err;
 286 }
 287
 288 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 289 {
 290         /* did we create it */
 291         if (inode->i_private != &thread)
 292                 return 0;
 293
 294         /* does the dev_t match */
 295         if (is_blockdev(dev)) {
 296                 if (!S_ISBLK(stat->mode))
 297                         return 0;
 298         } else {
 299                 if (!S_ISCHR(stat->mode))
 300                         return 0;
 301         }
 302         if (stat->rdev != dev->devt)
 303                 return 0;
 304
 305         /* ours */
 306         return 1;
 307 }
 308
 309 static int handle_remove(const char *nodename, struct device *dev)
 310 {
 311         struct path parent;
 312         struct dentry *dentry;
 313         int deleted = 0;
 314         int err;
 315
 316         dentry = kern_path_locked(nodename, &parent);
 317         if (IS_ERR(dentry))
 318                 return PTR_ERR(dentry);
 319
 320         if (d_really_is_positive(dentry)) {
 321                 struct kstat stat;
 322                 struct path p = {.mnt = parent.mnt, .dentry = dentry};
 323                 err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
 324                                   AT_STATX_SYNC_AS_STAT);
 325                 if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
 326                         struct iattr newattrs;
 327                         /*
 328                          * before unlinking this node, reset permissions
 329                          * of possible references like hardlinks
 330                          */
 331                         newattrs.ia_uid = GLOBAL_ROOT_UID;
 332                         newattrs.ia_gid = GLOBAL_ROOT_GID;
 333                         newattrs.ia_mode = stat.mode & ~0777;
 334                         newattrs.ia_valid =
 335                                 ATTR_UID|ATTR_GID|ATTR_MODE;
 336                         inode_lock(d_inode(dentry));
 337                         notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
 338                         inode_unlock(d_inode(dentry));
 339                         err = vfs_unlink(&nop_mnt_idmap, d_inode(parent.dentry),
 340                                          dentry, NULL);
 341                         if (!err || err == -ENOENT)
 342                                 deleted = 1;
 343                 }
 344         } else {
 345                 err = -ENOENT;
 346         }
 347         dput(dentry);
 348         inode_unlock(d_inode(parent.dentry));
 349
 350         path_put(&parent);
 351         if (deleted && strchr(nodename, '/'))
 352                 delete_path(nodename);
 353         return err;
 354 }
 355
 356 /*
 357  * If configured, or requested by the commandline, devtmpfs will be
 358  * auto-mounted after the kernel mounted the root filesystem.
 359  */
 360 int __init devtmpfs_mount(void)
 361 {
 362         int err;
 363
 364         if (!mount_dev)
 365                 return 0;
 366
 367         if (!thread)
 368                 return 0;
 369
 370         err = init_mount("devtmpfs", "dev", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
 371         if (err)
 372                 pr_info("error mounting %d\n", err);
 373         else
 374                 pr_info("mounted\n");
 375         return err;
 376 }
 377
 378 static __initdata DECLARE_COMPLETION(setup_done);
 379
 380 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
 381                   struct device *dev)
 382 {
 383         if (mode)
 384                 return handle_create(name, mode, uid, gid, dev);
 385         else
 386                 return handle_remove(name, dev);
 387 }
 388
 389 static void __noreturn devtmpfs_work_loop(void)
 390 {
 391         while (1) {
 392                 spin_lock(&req_lock);
 393                 while (requests) {
 394                         struct req *req = requests;
 395                         requests = NULL;
 396                         spin_unlock(&req_lock);
 397                         while (req) {
 398                                 struct req *next = req->next;
 399                                 req->err = handle(req->name, req->mode,
 400                                                   req->uid, req->gid, req->dev);
 401                                 complete(&req->done);
 402                                 req = next;
 403                         }
 404                         spin_lock(&req_lock);
 405                 }
 406                 __set_current_state(TASK_INTERRUPTIBLE);
 407                 spin_unlock(&req_lock);
 408                 schedule();
 409         }
 410 }
 411
 412 static noinline int __init devtmpfs_setup(void *p)
 413 {
 414         int err;
 415
 416         err = ksys_unshare(CLONE_NEWNS);
 417         if (err)
 418                 goto out;
 419         err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
 420         if (err)
 421                 goto out;
 422         init_chdir("/.."); /* will traverse into overmounted root */
 423         init_chroot(".");
 424 out:
 425         *(int *)p = err;
 426         return err;
 427 }
 428
 429 /*
 430  * The __ref is because devtmpfs_setup needs to be __init for the routines it
 431  * calls.  That call is done while devtmpfs_init, which is marked __init,
 432  * synchronously waits for it to complete.
 433  */
 434 static int __ref devtmpfsd(void *p)
 435 {
 436         int err = devtmpfs_setup(p);
 437
 438         complete(&setup_done);
 439         if (err)
 440                 return err;
 441         devtmpfs_work_loop();
 442         return 0;
 443 }
 444
 445 /*
 446  * Create devtmpfs instance, driver-core devices will add their device
 447  * nodes here.
 448  */
 449 int __init devtmpfs_init(void)
 450 {
 451         char opts[] = "mode=0755";
 452         int err;
 453
 454         mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
 455         if (IS_ERR(mnt)) {
 456                 pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt));
 457                 return PTR_ERR(mnt);
 458         }
 459         err = register_filesystem(&dev_fs_type);
 460         if (err) {
 461                 pr_err("unable to register devtmpfs type %d\n", err);
 462                 return err;
 463         }
 464
 465         thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
 466         if (!IS_ERR(thread)) {
 467                 wait_for_completion(&setup_done);
 468         } else {
 469                 err = PTR_ERR(thread);
 470                 thread = NULL;
 471         }
 472
 473         if (err) {
 474                 pr_err("unable to create devtmpfs %d\n", err);
 475                 unregister_filesystem(&dev_fs_type);
 476                 thread = NULL;
 477                 return err;
 478         }
 479
 480         pr_info("initialized\n");
 481         return 0;
 482 }