/* 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);

/**
 * binderfs_mount_opts - mount options for binderfs
 * @max: maximum number of allocatable binderfs binder devices
 */
struct binderfs_mount_opts {
        int max;
};

enum {
        Opt_max,
        Opt_err
};

static const match_table_t tokens = {
        { Opt_max, "max=%d" },
        { Opt_err, NULL     }
};

/**
 * 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.
 * @mount_opts:     The mount options in use.
 * @device_count:   The current number of allocated binder devices.
 */
struct binderfs_info {
        struct ipc_namespace *ipc_ns;
        struct dentry *control_dentry;
        kuid_t root_uid;
        kgid_t root_gid;
        struct binderfs_mount_opts mount_opts;
        int device_count;
};

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;

        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));

        /* 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 (!device)
                return;

        mutex_lock(&binderfs_minors_mutex);
        --info->device_count;
        ida_free(&binderfs_minors, device->miscdev.minor);
        mutex_unlock(&binderfs_minors_mutex);

        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;
        opts->max = BINDERFS_MAX_MINOR;

        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;
                default:
                        pr_err("Invalid mount options\n");
                        return -EINVAL;
                }
        }

        return 0;
}

static int binderfs_remount(struct super_block *sb, int *flags, char *data)
{
        struct binderfs_info *info = sb->s_fs_info;
        return binderfs_parse_mount_opts(data, &info->mount_opts);
}

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);

        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;

        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 int binderfs_fill_super(struct super_block *sb, void *data, int silent)
{
        int ret;
        struct binderfs_info *info;
        struct inode *inode = NULL;

        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;

        return binderfs_binder_ctl_create(sb);
}

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;

        /* 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;
}