/* -*- linux-c -*- --------------------------------------------------------- *
 *
 * linux/fs/devpts/inode.c
 *
 *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * ------------------------------------------------------------------------- */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/mount.h>
#include <linux/tty.h>
#include <linux/mutex.h>
#include <linux/magic.h>
#include <linux/idr.h>
#include <linux/devpts_fs.h>
#include <linux/parser.h>
#include <linux/fsnotify.h>
#include <linux/seq_file.h>

#define DEVPTS_DEFAULT_MODE 0600
/*
 * ptmx is a new node in /dev/pts and will be unused in legacy (single-
 * instance) mode. To prevent surprises in user space, set permissions of
 * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
 * permissions.
 */
#define DEVPTS_DEFAULT_PTMX_MODE 0000
#define PTMX_MINOR      2

/*
 * sysctl support for setting limits on the number of Unix98 ptys allocated.
 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 */
static int pty_limit = NR_UNIX98_PTY_DEFAULT;
static int pty_reserve = NR_UNIX98_PTY_RESERVE;
static int pty_limit_min;
static int pty_limit_max = INT_MAX;
static int pty_count;

static struct ctl_table pty_table[] = {
        {
                .procname       = "max",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .data           = &pty_limit,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &pty_limit_min,
                .extra2         = &pty_limit_max,
        }, {
                .procname       = "reserve",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .data           = &pty_reserve,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &pty_limit_min,
                .extra2         = &pty_limit_max,
        }, {
                .procname       = "nr",
                .maxlen         = sizeof(int),
                .mode           = 0444,
                .data           = &pty_count,
                .proc_handler   = proc_dointvec,
        },
        {}
};

static struct ctl_table pty_kern_table[] = {
        {
                .procname       = "pty",
                .mode           = 0555,
                .child          = pty_table,
        },
        {}
};

static struct ctl_table pty_root_table[] = {
        {
                .procname       = "kernel",
                .mode           = 0555,
                .child          = pty_kern_table,
        },
        {}
};

static DEFINE_MUTEX(allocated_ptys_lock);

static struct vfsmount *devpts_mnt;

struct pts_mount_opts {
        int setuid;
        int setgid;
        kuid_t   uid;
        kgid_t   gid;
        umode_t mode;
        umode_t ptmxmode;
        int newinstance;
        int max;
};

enum {
        Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
        Opt_err
};

static const match_table_t tokens = {
        {Opt_uid, "uid=%u"},
        {Opt_gid, "gid=%u"},
        {Opt_mode, "mode=%o"},
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
        {Opt_ptmxmode, "ptmxmode=%o"},
        {Opt_newinstance, "newinstance"},
        {Opt_max, "max=%d"},
#endif
        {Opt_err, NULL}
};

struct pts_fs_info {
        struct ida allocated_ptys;
        struct pts_mount_opts mount_opts;
        struct super_block *sb;
        struct dentry *ptmx_dentry;
};

static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
{
        return sb->s_fs_info;
}

static inline struct super_block *pts_sb_from_inode(struct inode *inode)
{
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
        if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
                return inode->i_sb;
#endif
        if (!devpts_mnt)
                return NULL;
        return devpts_mnt->mnt_sb;
}

#define PARSE_MOUNT     0
#define PARSE_REMOUNT   1

/*
 * parse_mount_options():
 *      Set @opts to mount options specified in @data. If an option is not
 *      specified in @data, set it to its default value. The exception is
 *      'newinstance' option which can only be set/cleared on a mount (i.e.
 *      cannot be changed during remount).
 *
 * Note: @data may be NULL (in which case all options are set to default).
 */
static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
{
        char *p;
        kuid_t uid;
        kgid_t gid;

        opts->setuid  = 0;
        opts->setgid  = 0;
        opts->uid     = GLOBAL_ROOT_UID;
        opts->gid     = GLOBAL_ROOT_GID;
        opts->mode    = DEVPTS_DEFAULT_MODE;
        opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
        opts->max     = NR_UNIX98_PTY_MAX;

        /* newinstance makes sense only on initial mount */
        if (op == PARSE_MOUNT)
                opts->newinstance = 0;

        while ((p = strsep(&data, ",")) != NULL) {
                substring_t args[MAX_OPT_ARGS];
                int token;
                int option;

                if (!*p)
                        continue;

                token = match_token(p, tokens, args);
                switch (token) {
                case Opt_uid:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        uid = make_kuid(current_user_ns(), option);
                        if (!uid_valid(uid))
                                return -EINVAL;
                        opts->uid = uid;
                        opts->setuid = 1;
                        break;
                case Opt_gid:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        gid = make_kgid(current_user_ns(), option);
                        if (!gid_valid(gid))
                                return -EINVAL;
                        opts->gid = gid;
                        opts->setgid = 1;
                        break;
                case Opt_mode:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->mode = option & S_IALLUGO;
                        break;
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
                case Opt_ptmxmode:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->ptmxmode = option & S_IALLUGO;
                        break;
                case Opt_newinstance:
                        /* newinstance makes sense only on initial mount */
                        if (op == PARSE_MOUNT)
                                opts->newinstance = 1;
                        break;
                case Opt_max:
                        if (match_int(&args[0], &option) ||
                            option < 0 || option > NR_UNIX98_PTY_MAX)
                                return -EINVAL;
                        opts->max = option;
                        break;
#endif
                default:
                        pr_err("called with bogus options\n");
                        return -EINVAL;
                }
        }

        return 0;
}

#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
static int mknod_ptmx(struct super_block *sb)
{
        int mode;
        int rc = -ENOMEM;
        struct dentry *dentry;
        struct inode *inode;
        struct dentry *root = sb->s_root;
        struct pts_fs_info *fsi = DEVPTS_SB(sb);
        struct pts_mount_opts *opts = &fsi->mount_opts;
        kuid_t root_uid;
        kgid_t root_gid;

        root_uid = make_kuid(current_user_ns(), 0);
        root_gid = make_kgid(current_user_ns(), 0);
        if (!uid_valid(root_uid) || !gid_valid(root_gid))
                return -EINVAL;

        inode_lock(d_inode(root));

        /* If we have already created ptmx node, return */
        if (fsi->ptmx_dentry) {
                rc = 0;
                goto out;
        }

        dentry = d_alloc_name(root, "ptmx");
        if (!dentry) {
                pr_err("Unable to alloc dentry for ptmx node\n");
                goto out;
        }

        /*
         * Create a new 'ptmx' node in this mount of devpts.
         */
        inode = new_inode(sb);
        if (!inode) {
                pr_err("Unable to alloc inode for ptmx node\n");
                dput(dentry);
                goto out;
        }

        inode->i_ino = 2;
        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;

        mode = S_IFCHR|opts->ptmxmode;
        init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
        inode->i_uid = root_uid;
        inode->i_gid = root_gid;

        d_add(dentry, inode);

        fsi->ptmx_dentry = dentry;
        rc = 0;
out:
        inode_unlock(d_inode(root));
        return rc;
}

static void update_ptmx_mode(struct pts_fs_info *fsi)
{
        struct inode *inode;
        if (fsi->ptmx_dentry) {
                inode = d_inode(fsi->ptmx_dentry);
                inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
        }
}
#else
static inline void update_ptmx_mode(struct pts_fs_info *fsi)
{
        return;
}
#endif

static int devpts_remount(struct super_block *sb, int *flags, char *data)
{
        int err;
        struct pts_fs_info *fsi = DEVPTS_SB(sb);
        struct pts_mount_opts *opts = &fsi->mount_opts;

        sync_filesystem(sb);
        err = parse_mount_options(data, PARSE_REMOUNT, opts);

        /*
         * parse_mount_options() restores options to default values
         * before parsing and may have changed ptmxmode. So, update the
         * mode in the inode too. Bogus options don't fail the remount,
         * so do this even on error return.
         */
        update_ptmx_mode(fsi);

        return err;
}

static int devpts_show_options(struct seq_file *seq, struct dentry *root)
{
        struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
        struct pts_mount_opts *opts = &fsi->mount_opts;

        if (opts->setuid)
                seq_printf(seq, ",uid=%u",
                           from_kuid_munged(&init_user_ns, opts->uid));
        if (opts->setgid)
                seq_printf(seq, ",gid=%u",
                           from_kgid_munged(&init_user_ns, opts->gid));
        seq_printf(seq, ",mode=%03o", opts->mode);
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
        seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
        if (opts->max < NR_UNIX98_PTY_MAX)
                seq_printf(seq, ",max=%d", opts->max);
#endif

        return 0;
}

static const struct super_operations devpts_sops = {
        .statfs         = simple_statfs,
        .remount_fs     = devpts_remount,
        .show_options   = devpts_show_options,
};

static void *new_pts_fs_info(struct super_block *sb)
{
        struct pts_fs_info *fsi;

        fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
        if (!fsi)
                return NULL;

        ida_init(&fsi->allocated_ptys);
        fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
        fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
        fsi->sb = sb;

        return fsi;
}

static int
devpts_fill_super(struct super_block *s, void *data, int silent)
{
        struct inode *inode;

        s->s_blocksize = 1024;
        s->s_blocksize_bits = 10;
        s->s_magic = DEVPTS_SUPER_MAGIC;
        s->s_op = &devpts_sops;
        s->s_time_gran = 1;

        s->s_fs_info = new_pts_fs_info(s);
        if (!s->s_fs_info)
                goto fail;

        inode = new_inode(s);
        if (!inode)
                goto fail;
        inode->i_ino = 1;
        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
        inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
        inode->i_op = &simple_dir_inode_operations;
        inode->i_fop = &simple_dir_operations;
        set_nlink(inode, 2);

        s->s_root = d_make_root(inode);
        if (s->s_root)
                return 0;

        pr_err("get root dentry failed\n");

fail:
        return -ENOMEM;
}

#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
static int compare_init_pts_sb(struct super_block *s, void *p)
{
        if (devpts_mnt)
                return devpts_mnt->mnt_sb == s;
        return 0;
}

/*
 * devpts_mount()
 *
 *     If the '-o newinstance' mount option was specified, mount a new
 *     (private) instance of devpts.  PTYs created in this instance are
 *     independent of the PTYs in other devpts instances.
 *
 *     If the '-o newinstance' option was not specified, mount/remount the
 *     initial kernel mount of devpts.  This type of mount gives the
 *     legacy, single-instance semantics.
 *
 *     The 'newinstance' option is needed to support multiple namespace
 *     semantics in devpts while preserving backward compatibility of the
 *     current 'single-namespace' semantics. i.e all mounts of devpts
 *     without the 'newinstance' mount option should bind to the initial
 *     kernel mount, like mount_single().
 *
 *     Mounts with 'newinstance' option create a new, private namespace.
 *
 *     NOTE:
 *
 *     For single-mount semantics, devpts cannot use mount_single(),
 *     because mount_single()/sget() find and use the super-block from
 *     the most recent mount of devpts. But that recent mount may be a
 *     'newinstance' mount and mount_single() would pick the newinstance
 *     super-block instead of the initial super-block.
 */
static struct dentry *devpts_mount(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data)
{
        int error;
        struct pts_mount_opts opts;
        struct super_block *s;

        error = parse_mount_options(data, PARSE_MOUNT, &opts);
        if (error)
                return ERR_PTR(error);

        /* Require newinstance for all user namespace mounts to ensure
         * the mount options are not changed.
         */
        if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
                return ERR_PTR(-EINVAL);

        if (opts.newinstance)
                s = sget(fs_type, NULL, set_anon_super, flags, NULL);
        else
                s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
                         NULL);

        if (IS_ERR(s))
                return ERR_CAST(s);

        if (!s->s_root) {
                error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
                if (error)
                        goto out_undo_sget;
                s->s_flags |= MS_ACTIVE;
        }

        memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));

        error = mknod_ptmx(s);
        if (error)
                goto out_undo_sget;

        return dget(s->s_root);

out_undo_sget:
        deactivate_locked_super(s);
        return ERR_PTR(error);
}

#else
/*
 * This supports only the legacy single-instance semantics (no
 * multiple-instance semantics)
 */
static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
                const char *dev_name, void *data)
{
        return mount_single(fs_type, flags, data, devpts_fill_super);
}
#endif

static void devpts_kill_sb(struct super_block *sb)
{
        struct pts_fs_info *fsi = DEVPTS_SB(sb);

        ida_destroy(&fsi->allocated_ptys);
        kfree(fsi);
        kill_litter_super(sb);
}

static struct file_system_type devpts_fs_type = {
        .name           = "devpts",
        .mount          = devpts_mount,
        .kill_sb        = devpts_kill_sb,
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
        .fs_flags       = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
#endif
};

/*
 * The normal naming convention is simply /dev/pts/<number>; this conforms
 * to the System V naming convention
 */

int devpts_new_index(struct pts_fs_info *fsi)
{
        int index;
        int ida_ret;

        if (!fsi)
                return -ENODEV;

retry:
        if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
                return -ENOMEM;

        mutex_lock(&allocated_ptys_lock);
        if (pty_count >= pty_limit -
                        (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
                mutex_unlock(&allocated_ptys_lock);
                return -ENOSPC;
        }

        ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
        if (ida_ret < 0) {
                mutex_unlock(&allocated_ptys_lock);
                if (ida_ret == -EAGAIN)
                        goto retry;
                return -EIO;
        }

        if (index >= fsi->mount_opts.max) {
                ida_remove(&fsi->allocated_ptys, index);
                mutex_unlock(&allocated_ptys_lock);
                return -ENOSPC;
        }
        pty_count++;
        mutex_unlock(&allocated_ptys_lock);
        return index;
}

void devpts_kill_index(struct pts_fs_info *fsi, int idx)
{
        mutex_lock(&allocated_ptys_lock);
        ida_remove(&fsi->allocated_ptys, idx);
        pty_count--;
        mutex_unlock(&allocated_ptys_lock);
}

/*
 * pty code needs to hold extra references in case of last /dev/tty close
 */
struct pts_fs_info *devpts_get_ref(struct inode *ptmx_inode, struct file *file)
{
        struct super_block *sb;
        struct pts_fs_info *fsi;

        sb = pts_sb_from_inode(ptmx_inode);
        if (!sb)
                return NULL;
        fsi = DEVPTS_SB(sb);
        if (!fsi)
                return NULL;

        atomic_inc(&sb->s_active);
        return fsi;
}

void devpts_put_ref(struct pts_fs_info *fsi)
{
        deactivate_super(fsi->sb);
}

/**
 * devpts_pty_new -- create a new inode in /dev/pts/
 * @ptmx_inode: inode of the master
 * @device: major+minor of the node to be created
 * @index: used as a name of the node
 * @priv: what's given back by devpts_get_priv
 *
 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
 */
struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
{
        struct dentry *dentry;
        struct super_block *sb;
        struct inode *inode;
        struct dentry *root;
        struct pts_mount_opts *opts;
        char s[12];

        if (!fsi)
                return ERR_PTR(-ENODEV);

        sb = fsi->sb;
        root = sb->s_root;
        opts = &fsi->mount_opts;

        inode = new_inode(sb);
        if (!inode)
                return ERR_PTR(-ENOMEM);

        inode->i_ino = index + 3;
        inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
        inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
        init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));

        sprintf(s, "%d", index);

        dentry = d_alloc_name(root, s);
        if (dentry) {
                dentry->d_fsdata = priv;
                d_add(dentry, inode);
                fsnotify_create(d_inode(root), dentry);
        } else {
                iput(inode);
                dentry = ERR_PTR(-ENOMEM);
        }

        return dentry;
}

/**
 * devpts_get_priv -- get private data for a slave
 * @pts_inode: inode of the slave
 *
 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
 */
void *devpts_get_priv(struct dentry *dentry)
{
        WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
        return dentry->d_fsdata;
}

/**
 * devpts_pty_kill -- remove inode form /dev/pts/
 * @inode: inode of the slave to be removed
 *
 * This is an inverse operation of devpts_pty_new.
 */
void devpts_pty_kill(struct dentry *dentry)
{
        WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);

        dentry->d_fsdata = NULL;
        drop_nlink(dentry->d_inode);
        d_delete(dentry);
        dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
}

static int __init init_devpts_fs(void)
{
        int err = register_filesystem(&devpts_fs_type);
        struct ctl_table_header *table;

        if (!err) {
                struct vfsmount *mnt;

                table = register_sysctl_table(pty_root_table);
                mnt = kern_mount(&devpts_fs_type);
                if (IS_ERR(mnt)) {
                        err = PTR_ERR(mnt);
                        unregister_filesystem(&devpts_fs_type);
                        unregister_sysctl_table(table);
                } else {
                        devpts_mnt = mnt;
                }
        }
        return err;
}
module_init(init_devpts_fs)