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 file_system_type internal_fs_type = { 67 .name = "devtmpfs", 68 #ifdef CONFIG_TMPFS 69 .init_fs_context = shmem_init_fs_context, 70 #else 71 .init_fs_context = ramfs_init_fs_context, 72 #endif 73 .kill_sb = kill_litter_super, 74 }; 75 76 /* Simply take a ref on the existing mount */ 77 static int devtmpfs_get_tree(struct fs_context *fc) 78 { 79 struct super_block *sb = mnt->mnt_sb; 80 81 atomic_inc(&sb->s_active); 82 down_write(&sb->s_umount); 83 fc->root = dget(sb->s_root); 84 return 0; 85 } 86 87 /* Ops are filled in during init depending on underlying shmem or ramfs type */ 88 struct fs_context_operations devtmpfs_context_ops = {}; 89 90 /* Call the underlying initialization and set to our ops */ 91 static int devtmpfs_init_fs_context(struct fs_context *fc) 92 { 93 int ret; 94 #ifdef CONFIG_TMPFS 95 ret = shmem_init_fs_context(fc); 96 #else 97 ret = ramfs_init_fs_context(fc); 98 #endif 99 if (ret < 0) 100 return ret; 101 102 fc->ops = &devtmpfs_context_ops; 103 104 return 0; 105 } 106 107 static struct file_system_type dev_fs_type = { 108 .name = "devtmpfs", 109 .init_fs_context = devtmpfs_init_fs_context, 110 }; 111 112 static int devtmpfs_submit_req(struct req *req, const char *tmp) 113 { 114 init_completion(&req->done); 115 116 spin_lock(&req_lock); 117 req->next = requests; 118 requests = req; 119 spin_unlock(&req_lock); 120 121 wake_up_process(thread); 122 wait_for_completion(&req->done); 123 124 kfree(tmp); 125 126 return req->err; 127 } 128 129 int devtmpfs_create_node(struct device *dev) 130 { 131 const char *tmp = NULL; 132 struct req req; 133 134 if (!thread) 135 return 0; 136 137 req.mode = 0; 138 req.uid = GLOBAL_ROOT_UID; 139 req.gid = GLOBAL_ROOT_GID; 140 req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp); 141 if (!req.name) 142 return -ENOMEM; 143 144 if (req.mode == 0) 145 req.mode = 0600; 146 if (is_blockdev(dev)) 147 req.mode |= S_IFBLK; 148 else 149 req.mode |= S_IFCHR; 150 151 req.dev = dev; 152 153 return devtmpfs_submit_req(&req, tmp); 154 } 155 156 int devtmpfs_delete_node(struct device *dev) 157 { 158 const char *tmp = NULL; 159 struct req req; 160 161 if (!thread) 162 return 0; 163 164 req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp); 165 if (!req.name) 166 return -ENOMEM; 167 168 req.mode = 0; 169 req.dev = dev; 170 171 return devtmpfs_submit_req(&req, tmp); 172 } 173 174 static int dev_mkdir(const char *name, umode_t mode) 175 { 176 struct dentry *dentry; 177 struct path path; 178 int err; 179 180 dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY); 181 if (IS_ERR(dentry)) 182 return PTR_ERR(dentry); 183 184 err = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode); 185 if (!err) 186 /* mark as kernel-created inode */ 187 d_inode(dentry)->i_private = &thread; 188 done_path_create(&path, dentry); 189 return err; 190 } 191 192 static int create_path(const char *nodepath) 193 { 194 char *path; 195 char *s; 196 int err = 0; 197 198 /* parent directories do not exist, create them */ 199 path = kstrdup(nodepath, GFP_KERNEL); 200 if (!path) 201 return -ENOMEM; 202 203 s = path; 204 for (;;) { 205 s = strchr(s, '/'); 206 if (!s) 207 break; 208 s[0] = '\0'; 209 err = dev_mkdir(path, 0755); 210 if (err && err != -EEXIST) 211 break; 212 s[0] = '/'; 213 s++; 214 } 215 kfree(path); 216 return err; 217 } 218 219 static int handle_create(const char *nodename, umode_t mode, kuid_t uid, 220 kgid_t gid, struct device *dev) 221 { 222 struct dentry *dentry; 223 struct path path; 224 int err; 225 226 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0); 227 if (dentry == ERR_PTR(-ENOENT)) { 228 create_path(nodename); 229 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0); 230 } 231 if (IS_ERR(dentry)) 232 return PTR_ERR(dentry); 233 234 err = vfs_mknod(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode, 235 dev->devt); 236 if (!err) { 237 struct iattr newattrs; 238 239 newattrs.ia_mode = mode; 240 newattrs.ia_uid = uid; 241 newattrs.ia_gid = gid; 242 newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID; 243 inode_lock(d_inode(dentry)); 244 notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL); 245 inode_unlock(d_inode(dentry)); 246 247 /* mark as kernel-created inode */ 248 d_inode(dentry)->i_private = &thread; 249 } 250 done_path_create(&path, dentry); 251 return err; 252 } 253 254 static int dev_rmdir(const char *name) 255 { 256 struct path parent; 257 struct dentry *dentry; 258 int err; 259 260 dentry = kern_path_locked(name, &parent); 261 if (IS_ERR(dentry)) 262 return PTR_ERR(dentry); 263 if (d_really_is_positive(dentry)) { 264 if (d_inode(dentry)->i_private == &thread) 265 err = vfs_rmdir(&nop_mnt_idmap, d_inode(parent.dentry), 266 dentry); 267 else 268 err = -EPERM; 269 } else { 270 err = -ENOENT; 271 } 272 dput(dentry); 273 inode_unlock(d_inode(parent.dentry)); 274 path_put(&parent); 275 return err; 276 } 277 278 static int delete_path(const char *nodepath) 279 { 280 char *path; 281 int err = 0; 282 283 path = kstrdup(nodepath, GFP_KERNEL); 284 if (!path) 285 return -ENOMEM; 286 287 for (;;) { 288 char *base; 289 290 base = strrchr(path, '/'); 291 if (!base) 292 break; 293 base[0] = '\0'; 294 err = dev_rmdir(path); 295 if (err) 296 break; 297 } 298 299 kfree(path); 300 return err; 301 } 302 303 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat) 304 { 305 /* did we create it */ 306 if (inode->i_private != &thread) 307 return 0; 308 309 /* does the dev_t match */ 310 if (is_blockdev(dev)) { 311 if (!S_ISBLK(stat->mode)) 312 return 0; 313 } else { 314 if (!S_ISCHR(stat->mode)) 315 return 0; 316 } 317 if (stat->rdev != dev->devt) 318 return 0; 319 320 /* ours */ 321 return 1; 322 } 323 324 static int handle_remove(const char *nodename, struct device *dev) 325 { 326 struct path parent; 327 struct dentry *dentry; 328 int deleted = 0; 329 int err; 330 331 dentry = kern_path_locked(nodename, &parent); 332 if (IS_ERR(dentry)) 333 return PTR_ERR(dentry); 334 335 if (d_really_is_positive(dentry)) { 336 struct kstat stat; 337 struct path p = {.mnt = parent.mnt, .dentry = dentry}; 338 err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE, 339 AT_STATX_SYNC_AS_STAT); 340 if (!err && dev_mynode(dev, d_inode(dentry), &stat)) { 341 struct iattr newattrs; 342 /* 343 * before unlinking this node, reset permissions 344 * of possible references like hardlinks 345 */ 346 newattrs.ia_uid = GLOBAL_ROOT_UID; 347 newattrs.ia_gid = GLOBAL_ROOT_GID; 348 newattrs.ia_mode = stat.mode & ~0777; 349 newattrs.ia_valid = 350 ATTR_UID|ATTR_GID|ATTR_MODE; 351 inode_lock(d_inode(dentry)); 352 notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL); 353 inode_unlock(d_inode(dentry)); 354 err = vfs_unlink(&nop_mnt_idmap, d_inode(parent.dentry), 355 dentry, NULL); 356 if (!err || err == -ENOENT) 357 deleted = 1; 358 } 359 } else { 360 err = -ENOENT; 361 } 362 dput(dentry); 363 inode_unlock(d_inode(parent.dentry)); 364 365 path_put(&parent); 366 if (deleted && strchr(nodename, '/')) 367 delete_path(nodename); 368 return err; 369 } 370 371 /* 372 * If configured, or requested by the commandline, devtmpfs will be 373 * auto-mounted after the kernel mounted the root filesystem. 374 */ 375 int __init devtmpfs_mount(void) 376 { 377 int err; 378 379 if (!mount_dev) 380 return 0; 381 382 if (!thread) 383 return 0; 384 385 err = init_mount("devtmpfs", "dev", "devtmpfs", DEVTMPFS_MFLAGS, NULL); 386 if (err) 387 pr_info("error mounting %d\n", err); 388 else 389 pr_info("mounted\n"); 390 return err; 391 } 392 393 static __initdata DECLARE_COMPLETION(setup_done); 394 395 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid, 396 struct device *dev) 397 { 398 if (mode) 399 return handle_create(name, mode, uid, gid, dev); 400 else 401 return handle_remove(name, dev); 402 } 403 404 static void __noreturn devtmpfs_work_loop(void) 405 { 406 while (1) { 407 spin_lock(&req_lock); 408 while (requests) { 409 struct req *req = requests; 410 requests = NULL; 411 spin_unlock(&req_lock); 412 while (req) { 413 struct req *next = req->next; 414 req->err = handle(req->name, req->mode, 415 req->uid, req->gid, req->dev); 416 complete(&req->done); 417 req = next; 418 } 419 spin_lock(&req_lock); 420 } 421 __set_current_state(TASK_INTERRUPTIBLE); 422 spin_unlock(&req_lock); 423 schedule(); 424 } 425 } 426 427 static noinline int __init devtmpfs_setup(void *p) 428 { 429 int err; 430 431 err = ksys_unshare(CLONE_NEWNS); 432 if (err) 433 goto out; 434 err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL); 435 if (err) 436 goto out; 437 init_chdir("/.."); /* will traverse into overmounted root */ 438 init_chroot("."); 439 out: 440 *(int *)p = err; 441 return err; 442 } 443 444 /* 445 * The __ref is because devtmpfs_setup needs to be __init for the routines it 446 * calls. That call is done while devtmpfs_init, which is marked __init, 447 * synchronously waits for it to complete. 448 */ 449 static int __ref devtmpfsd(void *p) 450 { 451 int err = devtmpfs_setup(p); 452 453 complete(&setup_done); 454 if (err) 455 return err; 456 devtmpfs_work_loop(); 457 return 0; 458 } 459 460 /* 461 * Get the underlying (shmem/ramfs) context ops to build ours 462 */ 463 static int devtmpfs_configure_context(void) 464 { 465 struct fs_context *fc; 466 467 fc = fs_context_for_reconfigure(mnt->mnt_root, mnt->mnt_sb->s_flags, 468 MS_RMT_MASK); 469 if (IS_ERR(fc)) 470 return PTR_ERR(fc); 471 472 /* Set up devtmpfs_context_ops based on underlying type */ 473 devtmpfs_context_ops.free = fc->ops->free; 474 devtmpfs_context_ops.dup = fc->ops->dup; 475 devtmpfs_context_ops.parse_param = fc->ops->parse_param; 476 devtmpfs_context_ops.parse_monolithic = fc->ops->parse_monolithic; 477 devtmpfs_context_ops.get_tree = &devtmpfs_get_tree; 478 devtmpfs_context_ops.reconfigure = fc->ops->reconfigure; 479 480 put_fs_context(fc); 481 482 return 0; 483 } 484 485 /* 486 * Create devtmpfs instance, driver-core devices will add their device 487 * nodes here. 488 */ 489 int __init devtmpfs_init(void) 490 { 491 char opts[] = "mode=0755"; 492 int err; 493 494 mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts); 495 if (IS_ERR(mnt)) { 496 pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt)); 497 return PTR_ERR(mnt); 498 } 499 500 err = devtmpfs_configure_context(); 501 if (err) { 502 pr_err("unable to configure devtmpfs type %d\n", err); 503 return err; 504 } 505 506 err = register_filesystem(&dev_fs_type); 507 if (err) { 508 pr_err("unable to register devtmpfs type %d\n", err); 509 return err; 510 } 511 512 thread = kthread_run(devtmpfsd, &err, "kdevtmpfs"); 513 if (!IS_ERR(thread)) { 514 wait_for_completion(&setup_done); 515 } else { 516 err = PTR_ERR(thread); 517 thread = NULL; 518 } 519 520 if (err) { 521 pr_err("unable to create devtmpfs %d\n", err); 522 unregister_filesystem(&dev_fs_type); 523 thread = NULL; 524 return err; 525 } 526 527 pr_info("initialized\n"); 528 return 0; 529 } 530