diff options
Diffstat (limited to '')
| -rw-r--r-- | drivers/base/devtmpfs.c | 482 |
1 files changed, 482 insertions, 0 deletions
diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c new file mode 100644 index 0000000000..b848764ef0 --- /dev/null +++ b/drivers/base/devtmpfs.c @@ -0,0 +1,482 @@ +// 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. + */ + +#define pr_fmt(fmt) "devtmpfs: " fmt + +#include <linux/kernel.h> +#include <linux/syscalls.h> +#include <linux/mount.h> +#include <linux/device.h> +#include <linux/blkdev.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" + +#ifdef CONFIG_DEVTMPFS_SAFE +#define DEVTMPFS_MFLAGS (MS_SILENT | MS_NOEXEC | MS_NOSUID) +#else +#define DEVTMPFS_MFLAGS (MS_SILENT) +#endif + +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; + int err; + + atomic_inc(&s->s_active); + down_write(&s->s_umount); + err = reconfigure_single(s, flags, data); + if (err < 0) { + deactivate_locked_super(s); + return ERR_PTR(err); + } + 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, +#else + .init_fs_context = ramfs_init_fs_context, +#endif + .kill_sb = kill_litter_super, +}; + +static struct file_system_type dev_fs_type = { + .name = "devtmpfs", + .mount = public_dev_mount, +}; + +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(&nop_mnt_idmap, 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(&nop_mnt_idmap, 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(&nop_mnt_idmap, 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(&nop_mnt_idmap, 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(&nop_mnt_idmap, dentry, &newattrs, NULL); + inode_unlock(d_inode(dentry)); + err = vfs_unlink(&nop_mnt_idmap, 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", DEVTMPFS_MFLAGS, NULL); + if (err) + pr_info("error mounting %d\n", err); + else + pr_info("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", DEVTMPFS_MFLAGS, 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)) { + pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt)); + return PTR_ERR(mnt); + } + err = register_filesystem(&dev_fs_type); + if (err) { + pr_err("unable to register devtmpfs type %d\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) { + pr_err("unable to create devtmpfs %d\n", err); + unregister_filesystem(&dev_fs_type); + thread = NULL; + return err; + } + + pr_info("initialized\n"); + return 0; +} |