inode.c

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/* -*- 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.
 *
 * ------------------------------------------------------------------------- */

#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 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
    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:
            printk(KERN_ERR "devpts: 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;

    mutex_lock(&root->d_inode->i_mutex);

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

    dentry = d_alloc_name(root, "ptmx");
    if (!dentry) {
        printk(KERN_NOTICE "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) {
        printk(KERN_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));

    d_add(dentry, inode);

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

static void update_ptmx_mode(struct pts_fs_info *fsi)
{
    struct inode *inode;
    if (fsi->ptmx_dentry) {
        inode = fsi->ptmx_dentry->d_inode;
        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;

    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(void)
{
    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;

    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();
    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;

    printk(KERN_ERR "devpts: 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);

    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);

    kfree(fsi);
    kill_litter_super(sb);
}

static struct file_system_type devpts_fs_type = {
    .name       = "devpts",
    .mount      = devpts_mount,
    .kill_sb    = devpts_kill_sb,
};

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

int devpts_new_index(struct inode *ptmx_inode)
{
    struct super_block *sb = pts_sb_from_inode(ptmx_inode);
    struct pts_fs_info *fsi = DEVPTS_SB(sb);
    int index;
    int ida_ret;

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 inode *ptmx_inode, int idx)
{
    struct super_block *sb = pts_sb_from_inode(ptmx_inode);
    struct pts_fs_info *fsi = DEVPTS_SB(sb);

    mutex_lock(&allocated_ptys_lock);
    ida_remove(&fsi->allocated_ptys, idx);
    pty_count--;
    mutex_unlock(&allocated_ptys_lock);
}

int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
{
    /* tty layer puts index from devpts_new_index() in here */
    int number = tty->index;
    struct tty_driver *driver = tty->driver;
    dev_t device = MKDEV(driver->major, driver->minor_start+number);
    struct dentry *dentry;
    struct super_block *sb = pts_sb_from_inode(ptmx_inode);
    struct inode *inode = new_inode(sb);
    struct dentry *root = sb->s_root;
    struct pts_fs_info *fsi = DEVPTS_SB(sb);
    struct pts_mount_opts *opts = &fsi->mount_opts;
    int ret = 0;
    char s[12];

    /* We're supposed to be given the slave end of a pty */
    BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
    BUG_ON(driver->subtype != PTY_TYPE_SLAVE);

    if (!inode)
        return -ENOMEM;

    inode->i_ino = number + 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, device);
    inode->i_private = tty;
    tty->driver_data = inode;

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

    mutex_lock(&root->d_inode->i_mutex);

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

    mutex_unlock(&root->d_inode->i_mutex);

    return ret;
}

struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
{
    struct dentry *dentry;
    struct tty_struct *tty;

    BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

    /* Ensure dentry has not been deleted by devpts_pty_kill() */
    dentry = d_find_alias(pts_inode);
    if (!dentry)
        return NULL;

    tty = NULL;
    if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
        tty = (struct tty_struct *)pts_inode->i_private;

    dput(dentry);

    return tty;
}

void devpts_pty_kill(struct tty_struct *tty)
{
    struct inode *inode = tty->driver_data;
    struct super_block *sb = pts_sb_from_inode(inode);
    struct dentry *root = sb->s_root;
    struct dentry *dentry;

    BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

    mutex_lock(&root->d_inode->i_mutex);

    dentry = d_find_alias(inode);

    drop_nlink(inode);
    d_delete(dentry);
    dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
    dput(dentry);       /* d_find_alias above */

    mutex_unlock(&root->d_inode->i_mutex);
}

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

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