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