linux/drivers/android/binderfs.c
Christian Brauner 211b64e4b5 binderfs: use refcount for binder control devices too
Binderfs binder-control devices are cleaned up via binderfs_evict_inode
too() which will use refcount_dec_and_test(). However, we missed to set
the refcount for binderfs binder-control devices and so we underflowed
when the binderfs instance got unmounted. Pretty obvious oversight and
should have been part of the more general UAF fix. The good news is that
having test cases (suprisingly) helps.

Technically, we could detect that we're about to cleanup the
binder-control dentry in binderfs_evict_inode() and then simply clean it
up. But that makes the assumption that the binder driver itself will
never make use of a binderfs binder-control device after the binderfs
instance it belongs to has been unmounted and the superblock for it been
destroyed. While it is unlikely to ever come to this let's be on the
safe side. Performance-wise this also really doesn't matter since the
binder-control device is only every really when creating the binderfs
filesystem or creating additional binder devices. Both operations are
pretty rare.

Fixes: f0fe2c0f05 ("binder: prevent UAF for binderfs devices II")
Link: https://lore.kernel.org/r/CA+G9fYusdfg7PMfC9Xce-xLT7NiyKSbgojpK35GOm=Pf9jXXrA@mail.gmail.com
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Todd Kjos <tkjos@google.com>
Link: https://lore.kernel.org/r/20200311105309.1742827-1-christian.brauner@ubuntu.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-11 19:33:52 +01:00

795 lines
19 KiB
C

/* 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/namei.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/seq_file.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/binderfs.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)
/* Ensure that the initial ipc namespace always has devices available. */
#define BINDERFS_MAX_MINOR_CAPPED (BINDERFS_MAX_MINOR - 4)
static dev_t binderfs_dev;
static DEFINE_MUTEX(binderfs_minors_mutex);
static DEFINE_IDA(binderfs_minors);
enum {
Opt_max,
Opt_stats_mode,
Opt_err
};
enum binderfs_stats_mode {
STATS_NONE,
STATS_GLOBAL,
};
static const match_table_t tokens = {
{ Opt_max, "max=%d" },
{ Opt_stats_mode, "stats=%s" },
{ Opt_err, NULL }
};
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 allocates 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, *root;
struct binder_device *device;
char *name = NULL;
size_t name_len;
struct inode *inode = NULL;
struct super_block *sb = ref_inode->i_sb;
struct binderfs_info *info = sb->s_fs_info;
#if defined(CONFIG_IPC_NS)
bool use_reserve = (info->ipc_ns == &init_ipc_ns);
#else
bool use_reserve = true;
#endif
/* Reserve new minor number for the new device. */
mutex_lock(&binderfs_minors_mutex);
if (++info->device_count <= info->mount_opts.max)
minor = ida_alloc_max(&binderfs_minors,
use_reserve ? BINDERFS_MAX_MINOR :
BINDERFS_MAX_MINOR_CAPPED,
GFP_KERNEL);
else
minor = -ENOSPC;
if (minor < 0) {
--info->device_count;
mutex_unlock(&binderfs_minors_mutex);
return minor;
}
mutex_unlock(&binderfs_minors_mutex);
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;
req->name[BINDERFS_MAX_NAME] = '\0'; /* NUL-terminate */
name_len = strlen(req->name);
/* Make sure to include terminating NUL byte */
name = kmemdup(req->name, name_len + 1, GFP_KERNEL);
if (!name)
goto err;
refcount_set(&device->ref, 1);
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;
if (userp && copy_to_user(userp, req, sizeof(*req))) {
ret = -EFAULT;
goto err;
}
root = sb->s_root;
inode_lock(d_inode(root));
/* look it up */
dentry = lookup_one_len(name, root, name_len);
if (IS_ERR(dentry)) {
inode_unlock(d_inode(root));
ret = PTR_ERR(dentry);
goto err;
}
if (d_really_is_positive(dentry)) {
/* already exists */
dput(dentry);
inode_unlock(d_inode(root));
ret = -EEXIST;
goto err;
}
inode->i_private = device;
d_instantiate(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);
--info->device_count;
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;
struct binderfs_info *info = BINDERFS_I(inode);
clear_inode(inode);
if (!S_ISCHR(inode->i_mode) || !device)
return;
mutex_lock(&binderfs_minors_mutex);
--info->device_count;
ida_free(&binderfs_minors, device->miscdev.minor);
mutex_unlock(&binderfs_minors_mutex);
if (refcount_dec_and_test(&device->ref)) {
kfree(device->context.name);
kfree(device);
}
}
/**
* binderfs_parse_mount_opts - parse binderfs mount options
* @data: options to set (can be NULL in which case defaults are used)
*/
static int binderfs_parse_mount_opts(char *data,
struct binderfs_mount_opts *opts)
{
char *p, *stats;
opts->max = BINDERFS_MAX_MINOR;
opts->stats_mode = STATS_NONE;
while ((p = strsep(&data, ",")) != NULL) {
substring_t args[MAX_OPT_ARGS];
int token;
int max_devices;
if (!*p)
continue;
token = match_token(p, tokens, args);
switch (token) {
case Opt_max:
if (match_int(&args[0], &max_devices) ||
(max_devices < 0 ||
(max_devices > BINDERFS_MAX_MINOR)))
return -EINVAL;
opts->max = max_devices;
break;
case Opt_stats_mode:
if (!capable(CAP_SYS_ADMIN))
return -EINVAL;
stats = match_strdup(&args[0]);
if (!stats)
return -ENOMEM;
if (strcmp(stats, "global") != 0) {
kfree(stats);
return -EINVAL;
}
opts->stats_mode = STATS_GLOBAL;
kfree(stats);
break;
default:
pr_err("Invalid mount options\n");
return -EINVAL;
}
}
return 0;
}
static int binderfs_remount(struct super_block *sb, int *flags, char *data)
{
int prev_stats_mode, ret;
struct binderfs_info *info = sb->s_fs_info;
prev_stats_mode = info->mount_opts.stats_mode;
ret = binderfs_parse_mount_opts(data, &info->mount_opts);
if (ret)
return ret;
if (prev_stats_mode != info->mount_opts.stats_mode) {
pr_err("Binderfs stats mode cannot be changed during a remount\n");
info->mount_opts.stats_mode = prev_stats_mode;
return -EINVAL;
}
return 0;
}
static int binderfs_show_mount_opts(struct seq_file *seq, struct dentry *root)
{
struct binderfs_info *info;
info = root->d_sb->s_fs_info;
if (info->mount_opts.max <= BINDERFS_MAX_MINOR)
seq_printf(seq, ",max=%d", info->mount_opts.max);
if (info->mount_opts.stats_mode == STATS_GLOBAL)
seq_printf(seq, ",stats=global");
return 0;
}
static const struct super_operations binderfs_super_ops = {
.evict_inode = binderfs_evict_inode,
.remount_fs = binderfs_remount,
.show_options = binderfs_show_mount_opts,
.statfs = simple_statfs,
};
static inline bool is_binderfs_control_device(const struct dentry *dentry)
{
struct binderfs_info *info = dentry->d_sb->s_fs_info;
return info->control_dentry == dentry;
}
static int binderfs_rename(struct inode *old_dir, struct dentry *old_dentry,
struct inode *new_dir, struct dentry *new_dentry,
unsigned int flags)
{
if (is_binderfs_control_device(old_dentry) ||
is_binderfs_control_device(new_dentry))
return -EPERM;
return simple_rename(old_dir, old_dentry, new_dir, new_dentry, flags);
}
static int binderfs_unlink(struct inode *dir, struct dentry *dentry)
{
if (is_binderfs_control_device(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;
#if defined(CONFIG_IPC_NS)
bool use_reserve = (info->ipc_ns == &init_ipc_ns);
#else
bool use_reserve = true;
#endif
device = kzalloc(sizeof(*device), GFP_KERNEL);
if (!device)
return -ENOMEM;
/* 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,
use_reserve ? BINDERFS_MAX_MINOR :
BINDERFS_MAX_MINOR_CAPPED,
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;
refcount_set(&device->ref, 1);
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);
return 0;
out:
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 struct inode *binderfs_make_inode(struct super_block *sb, int mode)
{
struct inode *ret;
ret = new_inode(sb);
if (ret) {
ret->i_ino = iunique(sb, BINDERFS_MAX_MINOR + INODE_OFFSET);
ret->i_mode = mode;
ret->i_atime = ret->i_mtime = ret->i_ctime = current_time(ret);
}
return ret;
}
static struct dentry *binderfs_create_dentry(struct dentry *parent,
const char *name)
{
struct dentry *dentry;
dentry = lookup_one_len(name, parent, strlen(name));
if (IS_ERR(dentry))
return dentry;
/* Return error if the file/dir already exists. */
if (d_really_is_positive(dentry)) {
dput(dentry);
return ERR_PTR(-EEXIST);
}
return dentry;
}
void binderfs_remove_file(struct dentry *dentry)
{
struct inode *parent_inode;
parent_inode = d_inode(dentry->d_parent);
inode_lock(parent_inode);
if (simple_positive(dentry)) {
dget(dentry);
simple_unlink(parent_inode, dentry);
d_delete(dentry);
dput(dentry);
}
inode_unlock(parent_inode);
}
struct dentry *binderfs_create_file(struct dentry *parent, const char *name,
const struct file_operations *fops,
void *data)
{
struct dentry *dentry;
struct inode *new_inode, *parent_inode;
struct super_block *sb;
parent_inode = d_inode(parent);
inode_lock(parent_inode);
dentry = binderfs_create_dentry(parent, name);
if (IS_ERR(dentry))
goto out;
sb = parent_inode->i_sb;
new_inode = binderfs_make_inode(sb, S_IFREG | 0444);
if (!new_inode) {
dput(dentry);
dentry = ERR_PTR(-ENOMEM);
goto out;
}
new_inode->i_fop = fops;
new_inode->i_private = data;
d_instantiate(dentry, new_inode);
fsnotify_create(parent_inode, dentry);
out:
inode_unlock(parent_inode);
return dentry;
}
static struct dentry *binderfs_create_dir(struct dentry *parent,
const char *name)
{
struct dentry *dentry;
struct inode *new_inode, *parent_inode;
struct super_block *sb;
parent_inode = d_inode(parent);
inode_lock(parent_inode);
dentry = binderfs_create_dentry(parent, name);
if (IS_ERR(dentry))
goto out;
sb = parent_inode->i_sb;
new_inode = binderfs_make_inode(sb, S_IFDIR | 0755);
if (!new_inode) {
dput(dentry);
dentry = ERR_PTR(-ENOMEM);
goto out;
}
new_inode->i_fop = &simple_dir_operations;
new_inode->i_op = &simple_dir_inode_operations;
set_nlink(new_inode, 2);
d_instantiate(dentry, new_inode);
inc_nlink(parent_inode);
fsnotify_mkdir(parent_inode, dentry);
out:
inode_unlock(parent_inode);
return dentry;
}
static int init_binder_logs(struct super_block *sb)
{
struct dentry *binder_logs_root_dir, *dentry, *proc_log_dir;
struct binderfs_info *info;
int ret = 0;
binder_logs_root_dir = binderfs_create_dir(sb->s_root,
"binder_logs");
if (IS_ERR(binder_logs_root_dir)) {
ret = PTR_ERR(binder_logs_root_dir);
goto out;
}
dentry = binderfs_create_file(binder_logs_root_dir, "stats",
&binder_stats_fops, NULL);
if (IS_ERR(dentry)) {
ret = PTR_ERR(dentry);
goto out;
}
dentry = binderfs_create_file(binder_logs_root_dir, "state",
&binder_state_fops, NULL);
if (IS_ERR(dentry)) {
ret = PTR_ERR(dentry);
goto out;
}
dentry = binderfs_create_file(binder_logs_root_dir, "transactions",
&binder_transactions_fops, NULL);
if (IS_ERR(dentry)) {
ret = PTR_ERR(dentry);
goto out;
}
dentry = binderfs_create_file(binder_logs_root_dir,
"transaction_log",
&binder_transaction_log_fops,
&binder_transaction_log);
if (IS_ERR(dentry)) {
ret = PTR_ERR(dentry);
goto out;
}
dentry = binderfs_create_file(binder_logs_root_dir,
"failed_transaction_log",
&binder_transaction_log_fops,
&binder_transaction_log_failed);
if (IS_ERR(dentry)) {
ret = PTR_ERR(dentry);
goto out;
}
proc_log_dir = binderfs_create_dir(binder_logs_root_dir, "proc");
if (IS_ERR(proc_log_dir)) {
ret = PTR_ERR(proc_log_dir);
goto out;
}
info = sb->s_fs_info;
info->proc_log_dir = proc_log_dir;
out:
return ret;
}
static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
{
int ret;
struct binderfs_info *info;
struct inode *inode = NULL;
struct binderfs_device device_info = { 0 };
const char *name;
size_t len;
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;
sb->s_fs_info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
if (!sb->s_fs_info)
return -ENOMEM;
info = sb->s_fs_info;
info->ipc_ns = get_ipc_ns(current->nsproxy->ipc_ns);
ret = binderfs_parse_mount_opts(data, &info->mount_opts);
if (ret)
return ret;
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;
inode = new_inode(sb);
if (!inode)
return -ENOMEM;
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)
return -ENOMEM;
ret = binderfs_binder_ctl_create(sb);
if (ret)
return ret;
name = binder_devices_param;
for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
strscpy(device_info.name, name, len + 1);
ret = binderfs_binder_device_create(inode, NULL, &device_info);
if (ret)
return ret;
name += len;
if (*name == ',')
name++;
}
if (info->mount_opts.stats_mode == STATS_GLOBAL)
return init_binder_logs(sb);
return 0;
}
static struct dentry *binderfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name,
void *data)
{
return mount_nodev(fs_type, flags, data, binderfs_fill_super);
}
static void binderfs_kill_super(struct super_block *sb)
{
struct binderfs_info *info = sb->s_fs_info;
kill_litter_super(sb);
if (info && info->ipc_ns)
put_ipc_ns(info->ipc_ns);
kfree(info);
}
static struct file_system_type binder_fs_type = {
.name = "binder",
.mount = binderfs_mount,
.kill_sb = binderfs_kill_super,
.fs_flags = FS_USERNS_MOUNT,
};
int __init init_binderfs(void)
{
int ret;
const char *name;
size_t len;
/* Verify that the default binderfs device names are valid. */
name = binder_devices_param;
for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
if (len > BINDERFS_MAX_NAME)
return -E2BIG;
name += len;
if (*name == ',')
name++;
}
/* 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;
}
return ret;
}