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// 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;
}