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 } 483