// SPDX-License-Identifier: GPL-2.0 /* * devtmpfs - kernel-maintained tmpfs-based /dev * * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org> * * During bootup, before any driver core device is registered, * devtmpfs, a tmpfs-based filesystem is created. Every driver-core * device which requests a device node, will add a node in this * filesystem. * By default, all devices are named after the name of the device, * owned by root and have a default mode of 0600. Subsystems can * overwrite the default setting if needed. */ #include <linux/kernel.h> #include <linux/syscalls.h> #include <linux/mount.h> #include <linux/device.h> #include <linux/genhd.h> #include <linux/namei.h> #include <linux/fs.h> #include <linux/shmem_fs.h> #include <linux/ramfs.h> #include <linux/sched.h> #include <linux/slab.h> #include <linux/kthread.h> #include <linux/init_syscalls.h> #include <uapi/linux/mount.h> #include "base.h" static struct task_struct *thread; static int __initdata mount_dev = IS_ENABLED(CONFIG_DEVTMPFS_MOUNT); static DEFINE_SPINLOCK(req_lock); static struct req { struct req *next; struct completion done; int err; const char *name; umode_t mode; /* 0 => delete */ kuid_t uid; kgid_t gid; struct device *dev; } *requests; static int __init mount_param(char *str) { mount_dev = simple_strtoul(str, NULL, 0); return 1; } __setup("devtmpfs.mount=", mount_param); static struct vfsmount *mnt; static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { struct super_block *s = mnt->mnt_sb; atomic_inc(&s->s_active); down_write(&s->s_umount); return dget(s->s_root); } static struct file_system_type internal_fs_type = { .name = "devtmpfs", #ifdef CONFIG_TMPFS .init_fs_context = shmem_init_fs_context, .parameters = shmem_fs_parameters, #else .init_fs_context = ramfs_init_fs_context, .parameters = ramfs_fs_parameters, #endif .kill_sb = kill_litter_super, }; static struct file_system_type dev_fs_type = { .name = "devtmpfs", .mount = public_dev_mount, }; #ifdef CONFIG_BLOCK static inline int is_blockdev(struct device *dev) { return dev->class == &block_class; } #else static inline int is_blockdev(struct device *dev) { return 0; } #endif static int devtmpfs_submit_req(struct req *req, const char *tmp) { init_completion(&req->done); spin_lock(&req_lock); req->next = requests; requests = req; spin_unlock(&req_lock); wake_up_process(thread); wait_for_completion(&req->done); kfree(tmp); return req->err; } int devtmpfs_create_node(struct device *dev) { const char *tmp = NULL; struct req req; if (!thread) return 0; req.mode = 0; req.uid = GLOBAL_ROOT_UID; req.gid = GLOBAL_ROOT_GID; req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp); if (!req.name) return -ENOMEM; if (req.mode == 0) req.mode = 0600; if (is_blockdev(dev)) req.mode |= S_IFBLK; else req.mode |= S_IFCHR; req.dev = dev; return devtmpfs_submit_req(&req, tmp); } int devtmpfs_delete_node(struct device *dev) { const char *tmp = NULL; struct req req; if (!thread) return 0; req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp); if (!req.name) return -ENOMEM; req.mode = 0; req.dev = dev; return devtmpfs_submit_req(&req, tmp); } static int dev_mkdir(const char *name, umode_t mode) { struct dentry *dentry; struct path path; int err; dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY); if (IS_ERR(dentry)) return PTR_ERR(dentry); err = vfs_mkdir(&init_user_ns, d_inode(path.dentry), dentry, mode); if (!err) /* mark as kernel-created inode */ d_inode(dentry)->i_private = &thread; done_path_create(&path, dentry); return err; } static int create_path(const char *nodepath) { char *path; char *s; int err = 0; /* parent directories do not exist, create them */ path = kstrdup(nodepath, GFP_KERNEL); if (!path) return -ENOMEM; s = path; for (;;) { s = strchr(s, '/'); if (!s) break; s[0] = '\0'; err = dev_mkdir(path, 0755); if (err && err != -EEXIST) break; s[0] = '/'; s++; } kfree(path); return err; } static int handle_create(const char *nodename, umode_t mode, kuid_t uid, kgid_t gid, struct device *dev) { struct dentry *dentry; struct path path; int err; dentry = kern_path_create(AT_FDCWD, nodename, &path, 0); if (dentry == ERR_PTR(-ENOENT)) { create_path(nodename); dentry = kern_path_create(AT_FDCWD, nodename, &path, 0); } if (IS_ERR(dentry)) return PTR_ERR(dentry); err = vfs_mknod(&init_user_ns, d_inode(path.dentry), dentry, mode, dev->devt); if (!err) { struct iattr newattrs; newattrs.ia_mode = mode; newattrs.ia_uid = uid; newattrs.ia_gid = gid; newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID; inode_lock(d_inode(dentry)); notify_change(&init_user_ns, dentry, &newattrs, NULL); inode_unlock(d_inode(dentry)); /* mark as kernel-created inode */ d_inode(dentry)->i_private = &thread; } done_path_create(&path, dentry); return err; } static int dev_rmdir(const char *name) { struct path parent; struct dentry *dentry; int err; dentry = kern_path_locked(name, &parent); if (IS_ERR(dentry)) return PTR_ERR(dentry); if (d_really_is_positive(dentry)) { if (d_inode(dentry)->i_private == &thread) err = vfs_rmdir(&init_user_ns, d_inode(parent.dentry), dentry); else err = -EPERM; } else { err = -ENOENT; } dput(dentry); inode_unlock(d_inode(parent.dentry)); path_put(&parent); return err; } static int delete_path(const char *nodepath) { char *path; int err = 0; path = kstrdup(nodepath, GFP_KERNEL); if (!path) return -ENOMEM; for (;;) { char *base; base = strrchr(path, '/'); if (!base) break; base[0] = '\0'; err = dev_rmdir(path); if (err) break; } kfree(path); return err; } static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat) { /* did we create it */ if (inode->i_private != &thread) return 0; /* does the dev_t match */ if (is_blockdev(dev)) { if (!S_ISBLK(stat->mode)) return 0; } else { if (!S_ISCHR(stat->mode)) return 0; } if (stat->rdev != dev->devt) return 0; /* ours */ return 1; } static int handle_remove(const char *nodename, struct device *dev) { struct path parent; struct dentry *dentry; int deleted = 0; int err; dentry = kern_path_locked(nodename, &parent); if (IS_ERR(dentry)) return PTR_ERR(dentry); if (d_really_is_positive(dentry)) { struct kstat stat; struct path p = {.mnt = parent.mnt, .dentry = dentry}; err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE, AT_STATX_SYNC_AS_STAT); if (!err && dev_mynode(dev, d_inode(dentry), &stat)) { struct iattr newattrs; /* * before unlinking this node, reset permissions * of possible references like hardlinks */ newattrs.ia_uid = GLOBAL_ROOT_UID; newattrs.ia_gid = GLOBAL_ROOT_GID; newattrs.ia_mode = stat.mode & ~0777; newattrs.ia_valid = ATTR_UID|ATTR_GID|ATTR_MODE; inode_lock(d_inode(dentry)); notify_change(&init_user_ns, dentry, &newattrs, NULL); inode_unlock(d_inode(dentry)); err = vfs_unlink(&init_user_ns, d_inode(parent.dentry), dentry, NULL); if (!err || err == -ENOENT) deleted = 1; } } else { err = -ENOENT; } dput(dentry); inode_unlock(d_inode(parent.dentry)); path_put(&parent); if (deleted && strchr(nodename, '/')) delete_path(nodename); return err; } /* * If configured, or requested by the commandline, devtmpfs will be * auto-mounted after the kernel mounted the root filesystem. */ int __init devtmpfs_mount(void) { int err; if (!mount_dev) return 0; if (!thread) return 0; err = init_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL); if (err) printk(KERN_INFO "devtmpfs: error mounting %i\n", err); else printk(KERN_INFO "devtmpfs: mounted\n"); return err; } static __initdata DECLARE_COMPLETION(setup_done); static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid, struct device *dev) { if (mode) return handle_create(name, mode, uid, gid, dev); else return handle_remove(name, dev); } static void __noreturn devtmpfs_work_loop(void) { while (1) { spin_lock(&req_lock); while (requests) { struct req *req = requests; requests = NULL; spin_unlock(&req_lock); while (req) { struct req *next = req->next; req->err = handle(req->name, req->mode, req->uid, req->gid, req->dev); complete(&req->done); req = next; } spin_lock(&req_lock); } __set_current_state(TASK_INTERRUPTIBLE); spin_unlock(&req_lock); schedule(); } } static noinline int __init devtmpfs_setup(void *p) { int err; err = ksys_unshare(CLONE_NEWNS); if (err) goto out; err = init_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL); if (err) goto out; init_chdir("/.."); /* will traverse into overmounted root */ init_chroot("."); out: *(int *)p = err; return err; } /* * The __ref is because devtmpfs_setup needs to be __init for the routines it * calls. That call is done while devtmpfs_init, which is marked __init, * synchronously waits for it to complete. */ static int __ref devtmpfsd(void *p) { int err = devtmpfs_setup(p); complete(&setup_done); if (err) return err; devtmpfs_work_loop(); return 0; } /* * Create devtmpfs instance, driver-core devices will add their device * nodes here. */ int __init devtmpfs_init(void) { char opts[] = "mode=0755"; int err; mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts); if (IS_ERR(mnt)) { printk(KERN_ERR "devtmpfs: unable to create devtmpfs %ld\n", PTR_ERR(mnt)); return PTR_ERR(mnt); } err = register_filesystem(&dev_fs_type); if (err) { printk(KERN_ERR "devtmpfs: unable to register devtmpfs " "type %i\n", err); return err; } thread = kthread_run(devtmpfsd, &err, "kdevtmpfs"); if (!IS_ERR(thread)) { wait_for_completion(&setup_done); } else { err = PTR_ERR(thread); thread = NULL; } if (err) { printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err); unregister_filesystem(&dev_fs_type); return err; } printk(KERN_INFO "devtmpfs: initialized\n"); return 0; }