/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/compiler_types.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/fsnotify.h>
#include <linux/gfp.h>
#include <linux/idr.h>
#include <linux/init.h>
#include <linux/ipc_namespace.h>
#include <linux/kdev_t.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/magic.h>
#include <linux/major.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/mount.h>
#include <linux/parser.h>
#include <linux/radix-tree.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock_types.h>
#include <linux/stddef.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <linux/user_namespace.h>
#include <linux/xarray.h>
#include <uapi/asm-generic/errno-base.h>
#include <uapi/linux/android/binder.h>
#include <uapi/linux/android/binder_ctl.h>
#include "binder_internal.h"
#define FIRST_INODE 1
#define SECOND_INODE 2
#define INODE_OFFSET 3
#define INTSTRLEN 21
#define BINDERFS_MAX_MINOR (1U << MINORBITS)
static struct vfsmount *binderfs_mnt;
static dev_t binderfs_dev;
static DEFINE_MUTEX(binderfs_minors_mutex);
static DEFINE_IDA(binderfs_minors);
/**
* binderfs_info - information about a binderfs mount
* @ipc_ns: The ipc namespace the binderfs mount belongs to.
* @control_dentry: This records the dentry of this binderfs mount
* binder-control device.
* @root_uid: uid that needs to be used when a new binder device is
* created.
* @root_gid: gid that needs to be used when a new binder device is
* created.
*/
struct binderfs_info {
struct ipc_namespace *ipc_ns;
struct dentry *control_dentry;
kuid_t root_uid;
kgid_t root_gid;
};
static inline struct binderfs_info *BINDERFS_I(const struct inode *inode)
{
return inode->i_sb->s_fs_info;
}
bool is_binderfs_device(const struct inode *inode)
{
if (inode->i_sb->s_magic == BINDERFS_SUPER_MAGIC)
return true;
return false;
}
/**
* binderfs_binder_device_create - allocate inode from super block of a
* binderfs mount
* @ref_inode: inode from wich the super block will be taken
* @userp: buffer to copy information about new device for userspace to
* @req: struct binderfs_device as copied from userspace
*
* This function allocated a new binder_device and reserves a new minor
* number for it.
* Minor numbers are limited and tracked globally in binderfs_minors. The
* function will stash a struct binder_device for the specific binder
* device in i_private of the inode.
* It will go on to allocate a new inode from the super block of the
* filesystem mount, stash a struct binder_device in its i_private field
* and attach a dentry to that inode.
*
* Return: 0 on success, negative errno on failure
*/
static int binderfs_binder_device_create(struct inode *ref_inode,
struct binderfs_device __user *userp,
struct binderfs_device *req)
{
int minor, ret;
struct dentry *dentry, *dup, *root;
struct binder_device *device;
size_t name_len = BINDERFS_MAX_NAME + 1;
char *name = NULL;
struct inode *inode = NULL;
struct super_block *sb = ref_inode->i_sb;
struct binderfs_info *info = sb->s_fs_info;
/* Reserve new minor number for the new device. */
mutex_lock(&binderfs_minors_mutex);
minor = ida_alloc_max(&binderfs_minors, BINDERFS_MAX_MINOR, GFP_KERNEL);
mutex_unlock(&binderfs_minors_mutex);
if (minor < 0)
return minor;
ret = -ENOMEM;
device = kzalloc(sizeof(*device), GFP_KERNEL);
if (!device)
goto err;
inode = new_inode(sb);
if (!inode)
goto err;
inode->i_ino = minor + INODE_OFFSET;
inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
init_special_inode(inode, S_IFCHR | 0600,
MKDEV(MAJOR(binderfs_dev), minor));
inode->i_fop = &binder_fops;
inode->i_uid = info->root_uid;
inode->i_gid = info->root_gid;
name = kmalloc(name_len, GFP_KERNEL);
if (!name)
goto err;
strscpy(name, req->name, name_len);
device->binderfs_inode = inode;
device->context.binder_context_mgr_uid = INVALID_UID;
device->context.name = name;
device->miscdev.name = name;
device->miscdev.minor = minor;
mutex_init(&device->context.context_mgr_node_lock);
req->major = MAJOR(binderfs_dev);
req->minor = minor;
ret = copy_to_user(userp, req, sizeof(*req));
if (ret) {
ret = -EFAULT;
goto err;
}
root = sb->s_root;
inode_lock(d_inode(root));
dentry = d_alloc_name(root, name);
if (!dentry) {
inode_unlock(d_inode(root));
ret = -ENOMEM;
goto err;
}
/* Verify that the name userspace gave us is not already in use. */
dup = d_lookup(root, &dentry->d_name);
if (dup) {
if (d_really_is_positive(dup)) {
dput(dup);
dput(dentry);
inode_unlock(d_inode(root));
ret = -EEXIST;
goto err;
}
dput(dup);
}
inode->i_private = device;
d_add(dentry, inode);
fsnotify_create(root->d_inode, dentry);
inode_unlock(d_inode(root));
return 0;
err:
kfree(name);
kfree(device);
mutex_lock(&binderfs_minors_mutex);
ida_free(&binderfs_minors, minor);
mutex_unlock(&binderfs_minors_mutex);
iput(inode);
return ret;
}
/**
* binderfs_ctl_ioctl - handle binder device node allocation requests
*
* The request handler for the binder-control device. All requests operate on
* the binderfs mount the binder-control device resides in:
* - BINDER_CTL_ADD
* Allocate a new binder device.
*
* Return: 0 on success, negative errno on failure
*/
static long binder_ctl_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
int ret = -EINVAL;
struct inode *inode = file_inode(file);
struct binderfs_device __user *device = (struct binderfs_device __user *)arg;
struct binderfs_device device_req;
switch (cmd) {
case BINDER_CTL_ADD:
ret = copy_from_user(&device_req, device, sizeof(device_req));
if (ret) {
ret = -EFAULT;
break;
}
ret = binderfs_binder_device_create(inode, device, &device_req);
break;
default:
break;
}
return ret;
}
static void binderfs_evict_inode(struct inode *inode)
{
struct binder_device *device = inode->i_private;
clear_inode(inode);
if (!device)
return;
mutex_lock(&binderfs_minors_mutex);
ida_free(&binderfs_minors, device->miscdev.minor);
mutex_unlock(&binderfs_minors_mutex);
kfree(device->context.name);
kfree(device);
}
static const struct super_operations binderfs_super_ops = {
.statfs = simple_statfs,
.evict_inode = binderfs_evict_inode,
};
static int binderfs_rename(struct inode *old_dir, struct dentry *old_dentry,
struct inode *new_dir, struct dentry *new_dentry,
unsigned int flags)
{
struct inode *inode = d_inode(old_dentry);
/* binderfs doesn't support directories. */
if (d_is_dir(old_dentry))
return -EPERM;
if (flags & ~RENAME_NOREPLACE)
return -EINVAL;
if (!simple_empty(new_dentry))
return -ENOTEMPTY;
if (d_really_is_positive(new_dentry))
simple_unlink(new_dir, new_dentry);
old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
return 0;
}
static int binderfs_unlink(struct inode *dir, struct dentry *dentry)
{
/*
* The control dentry is only ever touched during mount so checking it
* here should not require us to take lock.
*/
if (BINDERFS_I(dir)->control_dentry == dentry)
return -EPERM;
return simple_unlink(dir, dentry);
}
static const struct file_operations binder_ctl_fops = {
.owner = THIS_MODULE,
.open = nonseekable_open,
.unlocked_ioctl = binder_ctl_ioctl,
.compat_ioctl = binder_ctl_ioctl,
.llseek = noop_llseek,
};
/**
* binderfs_binder_ctl_create - create a new binder-control device
* @sb: super block of the binderfs mount
*
* This function creates a new binder-control device node in the binderfs mount
* referred to by @sb.
*
* Return: 0 on success, negative errno on failure
*/
static int binderfs_binder_ctl_create(struct super_block *sb)
{
int minor, ret;
struct dentry *dentry;
struct binder_device *device;
struct inode *inode = NULL;
struct dentry *root = sb->s_root;
struct binderfs_info *info = sb->s_fs_info;
device = kzalloc(sizeof(*device), GFP_KERNEL);
if (!device)
return -ENOMEM;
inode_lock(d_inode(root));
/* If we have already created a binder-control node, return. */
if (info->control_dentry) {
ret = 0;
goto out;
}
ret = -ENOMEM;
inode = new_inode(sb);
if (!inode)
goto out;
/* Reserve a new minor number for the new device. */
mutex_lock(&binderfs_minors_mutex);
minor = ida_alloc_max(&binderfs_minors, BINDERFS_MAX_MINOR, GFP_KERNEL);
mutex_unlock(&binderfs_minors_mutex);
if (minor < 0) {
ret = minor;
goto out;
}
inode->i_ino = SECOND_INODE;
inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
init_special_inode(inode, S_IFCHR | 0600,
MKDEV(MAJOR(binderfs_dev), minor));
inode->i_fop = &binder_ctl_fops;
inode->i_uid = info->root_uid;
inode->i_gid = info->root_gid;
device->binderfs_inode = inode;
device->miscdev.minor = minor;
dentry = d_alloc_name(root, "binder-control");
if (!dentry)
goto out;
inode->i_private = device;
info->control_dentry = dentry;
d_add(dentry, inode);
inode_unlock(d_inode(root));
return 0;
out:
inode_unlock(d_inode(root));
kfree(device);
iput(inode);
return ret;
}
static const struct inode_operations binderfs_dir_inode_operations = {
.lookup = simple_lookup,
.rename = binderfs_rename,
.unlink = binderfs_unlink,
};
static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
{
struct binderfs_info *info;
int ret = -ENOMEM;
struct inode *inode = NULL;
struct ipc_namespace *ipc_ns = sb->s_fs_info;
get_ipc_ns(ipc_ns);
sb->s_blocksize = PAGE_SIZE;
sb->s_blocksize_bits = PAGE_SHIFT;
/*
* The binderfs filesystem can be mounted by userns root in a
* non-initial userns. By default such mounts have the SB_I_NODEV flag
* set in s_iflags to prevent security issues where userns root can
* just create random device nodes via mknod() since it owns the
* filesystem mount. But binderfs does not allow to create any files
* including devices nodes. The only way to create binder devices nodes
* is through the binder-control device which userns root is explicitly
* allowed to do. So removing the SB_I_NODEV flag from s_iflags is both
* necessary and safe.
*/
sb->s_iflags &= ~SB_I_NODEV;
sb->s_iflags |= SB_I_NOEXEC;
sb->s_magic = BINDERFS_SUPER_MAGIC;
sb->s_op = &binderfs_super_ops;
sb->s_time_gran = 1;
info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
if (!info)
goto err_without_dentry;
info->ipc_ns = ipc_ns;
info->root_gid = make_kgid(sb->s_user_ns, 0);
if (!gid_valid(info->root_gid))
info->root_gid = GLOBAL_ROOT_GID;
info->root_uid = make_kuid(sb->s_user_ns, 0);
if (!uid_valid(info->root_uid))
info->root_uid = GLOBAL_ROOT_UID;
sb->s_fs_info = info;
inode = new_inode(sb);
if (!inode)
goto err_without_dentry;
inode->i_ino = FIRST_INODE;
inode->i_fop = &simple_dir_operations;
inode->i_mode = S_IFDIR | 0755;
inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
inode->i_op = &binderfs_dir_inode_operations;
set_nlink(inode, 2);
sb->s_root = d_make_root(inode);
if (!sb->s_root)
goto err_without_dentry;
ret = binderfs_binder_ctl_create(sb);
if (ret)
goto err_with_dentry;
return 0;
err_with_dentry:
dput(sb->s_root);
sb->s_root = NULL;
err_without_dentry:
put_ipc_ns(ipc_ns);
iput(inode);
kfree(info);
return ret;
}
static int binderfs_test_super(struct super_block *sb, void *data)
{
struct binderfs_info *info = sb->s_fs_info;
if (info)
return info->ipc_ns == data;
return 0;
}
static int binderfs_set_super(struct super_block *sb, void *data)
{
sb->s_fs_info = data;
return set_anon_super(sb, NULL);
}
static struct dentry *binderfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name,
void *data)
{
struct super_block *sb;
struct ipc_namespace *ipc_ns = current->nsproxy->ipc_ns;
if (!ns_capable(ipc_ns->user_ns, CAP_SYS_ADMIN))
return ERR_PTR(-EPERM);
sb = sget_userns(fs_type, binderfs_test_super, binderfs_set_super,
flags, ipc_ns->user_ns, ipc_ns);
if (IS_ERR(sb))
return ERR_CAST(sb);
if (!sb->s_root) {
int ret = binderfs_fill_super(sb, data, flags & SB_SILENT ? 1 : 0);
if (ret) {
deactivate_locked_super(sb);
return ERR_PTR(ret);
}
sb->s_flags |= SB_ACTIVE;
}
return dget(sb->s_root);
}
static void binderfs_kill_super(struct super_block *sb)
{
struct binderfs_info *info = sb->s_fs_info;
if (info && info->ipc_ns)
put_ipc_ns(info->ipc_ns);
kfree(info);
kill_litter_super(sb);
}
static struct file_system_type binder_fs_type = {
.name = "binder",
.mount = binderfs_mount,
.kill_sb = binderfs_kill_super,
.fs_flags = FS_USERNS_MOUNT,
};
static int __init init_binderfs(void)
{
int ret;
/* Allocate new major number for binderfs. */
ret = alloc_chrdev_region(&binderfs_dev, 0, BINDERFS_MAX_MINOR,
"binder");
if (ret)
return ret;
ret = register_filesystem(&binder_fs_type);
if (ret) {
unregister_chrdev_region(binderfs_dev, BINDERFS_MAX_MINOR);
return ret;
}
binderfs_mnt = kern_mount(&binder_fs_type);
if (IS_ERR(binderfs_mnt)) {
ret = PTR_ERR(binderfs_mnt);
binderfs_mnt = NULL;
unregister_filesystem(&binder_fs_type);
unregister_chrdev_region(binderfs_dev, BINDERFS_MAX_MINOR);
}
return ret;
}
device_initcall(init_binderfs);
