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; 178 179 dentry = start_creating_path(AT_FDCWD, name, &path, LOOKUP_DIRECTORY); 180 if (IS_ERR(dentry)) 181 return PTR_ERR(dentry); 182 183 dentry = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode); 184 if (!IS_ERR(dentry)) 185 /* mark as kernel-created inode */ 186 d_inode(dentry)->i_private = &thread; 187 end_creating_path(&path, dentry); 188 return PTR_ERR_OR_ZERO(dentry); 189 } 190 191 static int create_path(const char *nodepath) 192 { 193 char *path; 194 char *s; 195 int err = 0; 196 197 /* parent directories do not exist, create them */ 198 path = kstrdup(nodepath, GFP_KERNEL); 199 if (!path) 200 return -ENOMEM; 201 202 s = path; 203 for (;;) { 204 s = strchr(s, '/'); 205 if (!s) 206 break; 207 s[0] = '\0'; 208 err = dev_mkdir(path, 0755); 209 if (err && err != -EEXIST) 210 break; 211 s[0] = '/'; 212 s++; 213 } 214 kfree(path); 215 return err; 216 } 217 218 static int handle_create(const char *nodename, umode_t mode, kuid_t uid, 219 kgid_t gid, struct device *dev) 220 { 221 struct dentry *dentry; 222 struct path path; 223 int err; 224 225 dentry = start_creating_path(AT_FDCWD, nodename, &path, 0); 226 if (dentry == ERR_PTR(-ENOENT)) { 227 create_path(nodename); 228 dentry = start_creating_path(AT_FDCWD, nodename, &path, 0); 229 } 230 if (IS_ERR(dentry)) 231 return PTR_ERR(dentry); 232 233 err = vfs_mknod(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode, 234 dev->devt); 235 if (!err) { 236 struct iattr newattrs; 237 238 newattrs.ia_mode = mode; 239 newattrs.ia_uid = uid; 240 newattrs.ia_gid = gid; 241 newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID; 242 inode_lock(d_inode(dentry)); 243 notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL); 244 inode_unlock(d_inode(dentry)); 245 246 /* mark as kernel-created inode */ 247 d_inode(dentry)->i_private = &thread; 248 } 249 end_creating_path(&path, dentry); 250 return err; 251 } 252 253 static int dev_rmdir(const char *name) 254 { 255 struct path parent; 256 struct dentry *dentry; 257 int err; 258 259 dentry = start_removing_path(name, &parent); 260 if (IS_ERR(dentry)) 261 return PTR_ERR(dentry); 262 if (d_inode(dentry)->i_private == &thread) 263 err = vfs_rmdir(&nop_mnt_idmap, d_inode(parent.dentry), 264 dentry); 265 else 266 err = -EPERM; 267 268 end_removing_path(&parent, dentry); 269 return err; 270 } 271 272 static int delete_path(const char *nodepath) 273 { 274 char *path; 275 int err = 0; 276 277 path = kstrdup(nodepath, GFP_KERNEL); 278 if (!path) 279 return -ENOMEM; 280 281 for (;;) { 282 char *base; 283 284 base = strrchr(path, '/'); 285 if (!base) 286 break; 287 base[0] = '\0'; 288 err = dev_rmdir(path); 289 if (err) 290 break; 291 } 292 293 kfree(path); 294 return err; 295 } 296 297 static int dev_mynode(struct device *dev, struct inode *inode) 298 { 299 /* did we create it */ 300 if (inode->i_private != &thread) 301 return 0; 302 303 /* does the dev_t match */ 304 if (is_blockdev(dev)) { 305 if (!S_ISBLK(inode->i_mode)) 306 return 0; 307 } else { 308 if (!S_ISCHR(inode->i_mode)) 309 return 0; 310 } 311 if (inode->i_rdev != dev->devt) 312 return 0; 313 314 /* ours */ 315 return 1; 316 } 317 318 static int handle_remove(const char *nodename, struct device *dev) 319 { 320 struct path parent; 321 struct dentry *dentry; 322 struct inode *inode; 323 int deleted = 0; 324 int err = 0; 325 326 dentry = start_removing_path(nodename, &parent); 327 if (IS_ERR(dentry)) 328 return PTR_ERR(dentry); 329 330 inode = d_inode(dentry); 331 if (dev_mynode(dev, inode)) { 332 struct iattr newattrs; 333 /* 334 * before unlinking this node, reset permissions 335 * of possible references like hardlinks 336 */ 337 newattrs.ia_uid = GLOBAL_ROOT_UID; 338 newattrs.ia_gid = GLOBAL_ROOT_GID; 339 newattrs.ia_mode = inode->i_mode & ~0777; 340 newattrs.ia_valid = 341 ATTR_UID|ATTR_GID|ATTR_MODE; 342 inode_lock(d_inode(dentry)); 343 notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL); 344 inode_unlock(d_inode(dentry)); 345 err = vfs_unlink(&nop_mnt_idmap, d_inode(parent.dentry), 346 dentry, NULL); 347 if (!err || err == -ENOENT) 348 deleted = 1; 349 } 350 end_removing_path(&parent, dentry); 351 352 if (deleted && strchr(nodename, '/')) 353 delete_path(nodename); 354 return err; 355 } 356 357 /* 358 * If configured, or requested by the commandline, devtmpfs will be 359 * auto-mounted after the kernel mounted the root filesystem. 360 */ 361 int __init devtmpfs_mount(void) 362 { 363 int err; 364 365 if (!mount_dev) 366 return 0; 367 368 if (!thread) 369 return 0; 370 371 err = init_mount("devtmpfs", "dev", "devtmpfs", DEVTMPFS_MFLAGS, NULL); 372 if (err) 373 pr_info("error mounting %d\n", err); 374 else 375 pr_info("mounted\n"); 376 return err; 377 } 378 379 static __initdata DECLARE_COMPLETION(setup_done); 380 381 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid, 382 struct device *dev) 383 { 384 if (mode) 385 return handle_create(name, mode, uid, gid, dev); 386 else 387 return handle_remove(name, dev); 388 } 389 390 static void __noreturn devtmpfs_work_loop(void) 391 { 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 } 412 413 static noinline int __init devtmpfs_setup(void *p) 414 { 415 int err; 416 417 err = ksys_unshare(CLONE_NEWNS); 418 if (err) 419 goto out; 420 err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL); 421 if (err) 422 goto out; 423 init_chdir("/.."); /* will traverse into overmounted root */ 424 init_chroot("."); 425 out: 426 *(int *)p = err; 427 return err; 428 } 429 430 /* 431 * The __ref is because devtmpfs_setup needs to be __init for the routines it 432 * calls. That call is done while devtmpfs_init, which is marked __init, 433 * synchronously waits for it to complete. 434 */ 435 static int __ref devtmpfsd(void *p) 436 { 437 int err = devtmpfs_setup(p); 438 439 complete(&setup_done); 440 if (err) 441 return err; 442 devtmpfs_work_loop(); 443 return 0; 444 } 445 446 /* 447 * Get the underlying (shmem/ramfs) context ops to build ours 448 */ 449 static int devtmpfs_configure_context(void) 450 { 451 struct fs_context *fc; 452 453 fc = fs_context_for_reconfigure(mnt->mnt_root, mnt->mnt_sb->s_flags, 454 MS_RMT_MASK); 455 if (IS_ERR(fc)) 456 return PTR_ERR(fc); 457 458 /* Set up devtmpfs_context_ops based on underlying type */ 459 devtmpfs_context_ops.free = fc->ops->free; 460 devtmpfs_context_ops.dup = fc->ops->dup; 461 devtmpfs_context_ops.parse_param = fc->ops->parse_param; 462 devtmpfs_context_ops.parse_monolithic = fc->ops->parse_monolithic; 463 devtmpfs_context_ops.get_tree = &devtmpfs_get_tree; 464 devtmpfs_context_ops.reconfigure = fc->ops->reconfigure; 465 466 put_fs_context(fc); 467 468 return 0; 469 } 470 471 /* 472 * Create devtmpfs instance, driver-core devices will add their device 473 * nodes here. 474 */ 475 int __init devtmpfs_init(void) 476 { 477 char opts[] = "mode=0755"; 478 int err; 479 480 mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts); 481 if (IS_ERR(mnt)) { 482 pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt)); 483 return PTR_ERR(mnt); 484 } 485 486 err = devtmpfs_configure_context(); 487 if (err) { 488 pr_err("unable to configure devtmpfs type %d\n", err); 489 return err; 490 } 491 492 err = register_filesystem(&dev_fs_type); 493 if (err) { 494 pr_err("unable to register devtmpfs type %d\n", err); 495 return err; 496 } 497 498 thread = kthread_run(devtmpfsd, &err, "kdevtmpfs"); 499 if (!IS_ERR(thread)) { 500 wait_for_completion(&setup_done); 501 } else { 502 err = PTR_ERR(thread); 503 thread = NULL; 504 } 505 506 if (err) { 507 pr_err("unable to create devtmpfs %d\n", err); 508 unregister_filesystem(&dev_fs_type); 509 thread = NULL; 510 return err; 511 } 512 513 pr_info("initialized\n"); 514 return 0; 515 } 516