dev-ioctl.c

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/*
 * Copyright 2008 Red Hat, Inc. All rights reserved.
 * Copyright 2008 Ian Kent <[email protected]>
 *
 * 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/vmalloc.h>
#include <linux/miscdevice.h>
#include <linux/init.h>
#include <linux/wait.h>
#include <linux/namei.h>
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/sched.h>
#include <linux/compat.h>
#include <linux/syscalls.h>
#include <linux/magic.h>
#include <linux/dcache.h>
#include <linux/uaccess.h>
#include <linux/slab.h>

#include "autofs_i.h"

/*
 * This module implements an interface for routing autofs ioctl control
 * commands via a miscellaneous device file.
 *
 * The alternate interface is needed because we need to be able open
 * an ioctl file descriptor on an autofs mount that may be covered by
 * another mount. This situation arises when starting automount(8)
 * or other user space daemon which uses direct mounts or offset
 * mounts (used for autofs lazy mount/umount of nested mount trees),
 * which have been left busy at at service shutdown.
 */

#define AUTOFS_DEV_IOCTL_SIZE   sizeof(struct autofs_dev_ioctl)

typedef int (*ioctl_fn)(struct file *, struct autofs_sb_info *,
            struct autofs_dev_ioctl *);

static int check_name(const char *name)
{
    if (!strchr(name, '/'))
        return -EINVAL;
    return 0;
}

/*
 * Check a string doesn't overrun the chunk of
 * memory we copied from user land.
 */
static int invalid_str(char *str, size_t size)
{
    if (memchr(str, 0, size))
        return 0;
    return -EINVAL;
}

/*
 * Check that the user compiled against correct version of autofs
 * misc device code.
 *
 * As well as checking the version compatibility this always copies
 * the kernel interface version out.
 */
static int check_dev_ioctl_version(int cmd, struct autofs_dev_ioctl *param)
{
    int err = 0;

    if ((AUTOFS_DEV_IOCTL_VERSION_MAJOR != param->ver_major) ||
        (AUTOFS_DEV_IOCTL_VERSION_MINOR < param->ver_minor)) {
        AUTOFS_WARN("ioctl control interface version mismatch: "
             "kernel(%u.%u), user(%u.%u), cmd(%d)",
             AUTOFS_DEV_IOCTL_VERSION_MAJOR,
             AUTOFS_DEV_IOCTL_VERSION_MINOR,
             param->ver_major, param->ver_minor, cmd);
        err = -EINVAL;
    }

    /* Fill in the kernel version. */
    param->ver_major = AUTOFS_DEV_IOCTL_VERSION_MAJOR;
    param->ver_minor = AUTOFS_DEV_IOCTL_VERSION_MINOR;

    return err;
}

/*
 * Copy parameter control struct, including a possible path allocated
 * at the end of the struct.
 */
static struct autofs_dev_ioctl *copy_dev_ioctl(struct autofs_dev_ioctl __user *in)
{
    struct autofs_dev_ioctl tmp;

    if (copy_from_user(&tmp, in, sizeof(tmp)))
        return ERR_PTR(-EFAULT);

    if (tmp.size < sizeof(tmp))
        return ERR_PTR(-EINVAL);

    return memdup_user(in, tmp.size);
}

static inline void free_dev_ioctl(struct autofs_dev_ioctl *param)
{
    kfree(param);
    return;
}

/*
 * Check sanity of parameter control fields and if a path is present
 * check that it is terminated and contains at least one "/".
 */
static int validate_dev_ioctl(int cmd, struct autofs_dev_ioctl *param)
{
    int err;

    err = check_dev_ioctl_version(cmd, param);
    if (err) {
        AUTOFS_WARN("invalid device control module version "
             "supplied for cmd(0x%08x)", cmd);
        goto out;
    }

    if (param->size > sizeof(*param)) {
        err = invalid_str(param->path, param->size - sizeof(*param));
        if (err) {
            AUTOFS_WARN(
              "path string terminator missing for cmd(0x%08x)",
              cmd);
            goto out;
        }

        err = check_name(param->path);
        if (err) {
            AUTOFS_WARN("invalid path supplied for cmd(0x%08x)",
                    cmd);
            goto out;
        }
    }

    err = 0;
out:
    return err;
}

/*
 * Get the autofs super block info struct from the file opened on
 * the autofs mount point.
 */
static struct autofs_sb_info *autofs_dev_ioctl_sbi(struct file *f)
{
    struct autofs_sb_info *sbi = NULL;
    struct inode *inode;

    if (f) {
        inode = f->f_path.dentry->d_inode;
        sbi = autofs4_sbi(inode->i_sb);
    }
    return sbi;
}

/* Return autofs module protocol version */
static int autofs_dev_ioctl_protover(struct file *fp,
                     struct autofs_sb_info *sbi,
                     struct autofs_dev_ioctl *param)
{
    param->protover.version = sbi->version;
    return 0;
}

/* Return autofs module protocol sub version */
static int autofs_dev_ioctl_protosubver(struct file *fp,
                    struct autofs_sb_info *sbi,
                    struct autofs_dev_ioctl *param)
{
    param->protosubver.sub_version = sbi->sub_version;
    return 0;
}

static int find_autofs_mount(const char *pathname,
                 struct path *res,
                 int test(struct path *path, void *data),
                 void *data)
{
    struct path path;
    int err = kern_path(pathname, 0, &path);
    if (err)
        return err;
    err = -ENOENT;
    while (path.dentry == path.mnt->mnt_root) {
        if (path.dentry->d_sb->s_magic == AUTOFS_SUPER_MAGIC) {
            if (test(&path, data)) {
                path_get(&path);
                if (!err) /* already found some */
                    path_put(res);
                *res = path;
                err = 0;
            }
        }
        if (!follow_up(&path))
            break;
    }
    path_put(&path);
    return err;
}

static int test_by_dev(struct path *path, void *p)
{
    return path->dentry->d_sb->s_dev == *(dev_t *)p;
}

static int test_by_type(struct path *path, void *p)
{
    struct autofs_info *ino = autofs4_dentry_ino(path->dentry);
    return ino && ino->sbi->type & *(unsigned *)p;
}

/*
 * Open a file descriptor on the autofs mount point corresponding
 * to the given path and device number (aka. new_encode_dev(sb->s_dev)).
 */
static int autofs_dev_ioctl_open_mountpoint(const char *name, dev_t devid)
{
    int err, fd;

    fd = get_unused_fd_flags(O_CLOEXEC);
    if (likely(fd >= 0)) {
        struct file *filp;
        struct path path;

        err = find_autofs_mount(name, &path, test_by_dev, &devid);
        if (err)
            goto out;

        /*
         * Find autofs super block that has the device number
         * corresponding to the autofs fs we want to open.
         */

        filp = dentry_open(&path, O_RDONLY, current_cred());
        path_put(&path);
        if (IS_ERR(filp)) {
            err = PTR_ERR(filp);
            goto out;
        }

        fd_install(fd, filp);
    }

    return fd;

out:
    put_unused_fd(fd);
    return err;
}

/* Open a file descriptor on an autofs mount point */
static int autofs_dev_ioctl_openmount(struct file *fp,
                      struct autofs_sb_info *sbi,
                      struct autofs_dev_ioctl *param)
{
    const char *path;
    dev_t devid;
    int err, fd;

    /* param->path has already been checked */
    if (!param->openmount.devid)
        return -EINVAL;

    param->ioctlfd = -1;

    path = param->path;
    devid = new_decode_dev(param->openmount.devid);

    err = 0;
    fd = autofs_dev_ioctl_open_mountpoint(path, devid);
    if (unlikely(fd < 0)) {
        err = fd;
        goto out;
    }

    param->ioctlfd = fd;
out:
    return err;
}

/* Close file descriptor allocated above (user can also use close(2)). */
static int autofs_dev_ioctl_closemount(struct file *fp,
                       struct autofs_sb_info *sbi,
                       struct autofs_dev_ioctl *param)
{
    return sys_close(param->ioctlfd);
}

/*
 * Send "ready" status for an existing wait (either a mount or an expire
 * request).
 */
static int autofs_dev_ioctl_ready(struct file *fp,
                  struct autofs_sb_info *sbi,
                  struct autofs_dev_ioctl *param)
{
    autofs_wqt_t token;

    token = (autofs_wqt_t) param->ready.token;
    return autofs4_wait_release(sbi, token, 0);
}

/*
 * Send "fail" status for an existing wait (either a mount or an expire
 * request).
 */
static int autofs_dev_ioctl_fail(struct file *fp,
                 struct autofs_sb_info *sbi,
                 struct autofs_dev_ioctl *param)
{
    autofs_wqt_t token;
    int status;

    token = (autofs_wqt_t) param->fail.token;
    status = param->fail.status ? param->fail.status : -ENOENT;
    return autofs4_wait_release(sbi, token, status);
}

/*
 * Set the pipe fd for kernel communication to the daemon.
 *
 * Normally this is set at mount using an option but if we
 * are reconnecting to a busy mount then we need to use this
 * to tell the autofs mount about the new kernel pipe fd. In
 * order to protect mounts against incorrectly setting the
 * pipefd we also require that the autofs mount be catatonic.
 *
 * This also sets the process group id used to identify the
 * controlling process (eg. the owning automount(8) daemon).
 */
static int autofs_dev_ioctl_setpipefd(struct file *fp,
                      struct autofs_sb_info *sbi,
                      struct autofs_dev_ioctl *param)
{
    int pipefd;
    int err = 0;

    if (param->setpipefd.pipefd == -1)
        return -EINVAL;

    pipefd = param->setpipefd.pipefd;

    mutex_lock(&sbi->wq_mutex);
    if (!sbi->catatonic) {
        mutex_unlock(&sbi->wq_mutex);
        return -EBUSY;
    } else {
        struct file *pipe = fget(pipefd);
        if (!pipe) {
            err = -EBADF;
            goto out;
        }
        if (autofs_prepare_pipe(pipe) < 0) {
            err = -EPIPE;
            fput(pipe);
            goto out;
        }
        sbi->oz_pgrp = task_pgrp_nr(current);
        sbi->pipefd = pipefd;
        sbi->pipe = pipe;
        sbi->catatonic = 0;
    }
out:
    mutex_unlock(&sbi->wq_mutex);
    return err;
}

/*
 * Make the autofs mount point catatonic, no longer responsive to
 * mount requests. Also closes the kernel pipe file descriptor.
 */
static int autofs_dev_ioctl_catatonic(struct file *fp,
                      struct autofs_sb_info *sbi,
                      struct autofs_dev_ioctl *param)
{
    autofs4_catatonic_mode(sbi);
    return 0;
}

/* Set the autofs mount timeout */
static int autofs_dev_ioctl_timeout(struct file *fp,
                    struct autofs_sb_info *sbi,
                    struct autofs_dev_ioctl *param)
{
    unsigned long timeout;

    timeout = param->timeout.timeout;
    param->timeout.timeout = sbi->exp_timeout / HZ;
    sbi->exp_timeout = timeout * HZ;
    return 0;
}

/*
 * Return the uid and gid of the last request for the mount
 *
 * When reconstructing an autofs mount tree with active mounts
 * we need to re-connect to mounts that may have used the original
 * process uid and gid (or string variations of them) for mount
 * lookups within the map entry.
 */
static int autofs_dev_ioctl_requester(struct file *fp,
                      struct autofs_sb_info *sbi,
                      struct autofs_dev_ioctl *param)
{
    struct autofs_info *ino;
    struct path path;
    dev_t devid;
    int err = -ENOENT;

    if (param->size <= sizeof(*param)) {
        err = -EINVAL;
        goto out;
    }

    devid = sbi->sb->s_dev;

    param->requester.uid = param->requester.gid = -1;

    err = find_autofs_mount(param->path, &path, test_by_dev, &devid);
    if (err)
        goto out;

    ino = autofs4_dentry_ino(path.dentry);
    if (ino) {
        err = 0;
        autofs4_expire_wait(path.dentry);
        spin_lock(&sbi->fs_lock);
        param->requester.uid = ino->uid;
        param->requester.gid = ino->gid;
        spin_unlock(&sbi->fs_lock);
    }
    path_put(&path);
out:
    return err;
}

/*
 * Call repeatedly until it returns -EAGAIN, meaning there's nothing
 * more that can be done.
 */
static int autofs_dev_ioctl_expire(struct file *fp,
                   struct autofs_sb_info *sbi,
                   struct autofs_dev_ioctl *param)
{
    struct vfsmount *mnt;
    int how;

    how = param->expire.how;
    mnt = fp->f_path.mnt;

    return autofs4_do_expire_multi(sbi->sb, mnt, sbi, how);
}

/* Check if autofs mount point is in use */
static int autofs_dev_ioctl_askumount(struct file *fp,
                      struct autofs_sb_info *sbi,
                      struct autofs_dev_ioctl *param)
{
    param->askumount.may_umount = 0;
    if (may_umount(fp->f_path.mnt))
        param->askumount.may_umount = 1;
    return 0;
}

/*
 * Check if the given path is a mountpoint.
 *
 * If we are supplied with the file descriptor of an autofs
 * mount we're looking for a specific mount. In this case
 * the path is considered a mountpoint if it is itself a
 * mountpoint or contains a mount, such as a multi-mount
 * without a root mount. In this case we return 1 if the
 * path is a mount point and the super magic of the covering
 * mount if there is one or 0 if it isn't a mountpoint.
 *
 * If we aren't supplied with a file descriptor then we
 * lookup the nameidata of the path and check if it is the
 * root of a mount. If a type is given we are looking for
 * a particular autofs mount and if we don't find a match
 * we return fail. If the located nameidata path is the
 * root of a mount we return 1 along with the super magic
 * of the mount or 0 otherwise.
 *
 * In both cases the the device number (as returned by
 * new_encode_dev()) is also returned.
 */
static int autofs_dev_ioctl_ismountpoint(struct file *fp,
                     struct autofs_sb_info *sbi,
                     struct autofs_dev_ioctl *param)
{
    struct path path;
    const char *name;
    unsigned int type;
    unsigned int devid, magic;
    int err = -ENOENT;

    if (param->size <= sizeof(*param)) {
        err = -EINVAL;
        goto out;
    }

    name = param->path;
    type = param->ismountpoint.in.type;

    param->ismountpoint.out.devid = devid = 0;
    param->ismountpoint.out.magic = magic = 0;

    if (!fp || param->ioctlfd == -1) {
        if (autofs_type_any(type))
            err = kern_path(name, LOOKUP_FOLLOW, &path);
        else
            err = find_autofs_mount(name, &path, test_by_type, &type);
        if (err)
            goto out;
        devid = new_encode_dev(path.dentry->d_sb->s_dev);
        err = 0;
        if (path.mnt->mnt_root == path.dentry) {
            err = 1;
            magic = path.dentry->d_sb->s_magic;
        }
    } else {
        dev_t dev = sbi->sb->s_dev;

        err = find_autofs_mount(name, &path, test_by_dev, &dev);
        if (err)
            goto out;

        devid = new_encode_dev(dev);

        err = have_submounts(path.dentry);

        if (follow_down_one(&path))
            magic = path.dentry->d_sb->s_magic;
    }

    param->ismountpoint.out.devid = devid;
    param->ismountpoint.out.magic = magic;
    path_put(&path);
out:
    return err;
}

/*
 * Our range of ioctl numbers isn't 0 based so we need to shift
 * the array index by _IOC_NR(AUTOFS_CTL_IOC_FIRST) for the table
 * lookup.
 */
#define cmd_idx(cmd)    (cmd - _IOC_NR(AUTOFS_DEV_IOCTL_IOC_FIRST))

static ioctl_fn lookup_dev_ioctl(unsigned int cmd)
{
    static struct {
        int cmd;
        ioctl_fn fn;
    } _ioctls[] = {
        {cmd_idx(AUTOFS_DEV_IOCTL_VERSION_CMD), NULL},
        {cmd_idx(AUTOFS_DEV_IOCTL_PROTOVER_CMD),
             autofs_dev_ioctl_protover},
        {cmd_idx(AUTOFS_DEV_IOCTL_PROTOSUBVER_CMD),
             autofs_dev_ioctl_protosubver},
        {cmd_idx(AUTOFS_DEV_IOCTL_OPENMOUNT_CMD),
             autofs_dev_ioctl_openmount},
        {cmd_idx(AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD),
             autofs_dev_ioctl_closemount},
        {cmd_idx(AUTOFS_DEV_IOCTL_READY_CMD),
             autofs_dev_ioctl_ready},
        {cmd_idx(AUTOFS_DEV_IOCTL_FAIL_CMD),
             autofs_dev_ioctl_fail},
        {cmd_idx(AUTOFS_DEV_IOCTL_SETPIPEFD_CMD),
             autofs_dev_ioctl_setpipefd},
        {cmd_idx(AUTOFS_DEV_IOCTL_CATATONIC_CMD),
             autofs_dev_ioctl_catatonic},
        {cmd_idx(AUTOFS_DEV_IOCTL_TIMEOUT_CMD),
             autofs_dev_ioctl_timeout},
        {cmd_idx(AUTOFS_DEV_IOCTL_REQUESTER_CMD),
             autofs_dev_ioctl_requester},
        {cmd_idx(AUTOFS_DEV_IOCTL_EXPIRE_CMD),
             autofs_dev_ioctl_expire},
        {cmd_idx(AUTOFS_DEV_IOCTL_ASKUMOUNT_CMD),
             autofs_dev_ioctl_askumount},
        {cmd_idx(AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD),
             autofs_dev_ioctl_ismountpoint}
    };
    unsigned int idx = cmd_idx(cmd);

    return (idx >= ARRAY_SIZE(_ioctls)) ? NULL : _ioctls[idx].fn;
}

/* ioctl dispatcher */
static int _autofs_dev_ioctl(unsigned int command, struct autofs_dev_ioctl __user *user)
{
    struct autofs_dev_ioctl *param;
    struct file *fp;
    struct autofs_sb_info *sbi;
    unsigned int cmd_first, cmd;
    ioctl_fn fn = NULL;
    int err = 0;

    /* only root can play with this */
    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    cmd_first = _IOC_NR(AUTOFS_DEV_IOCTL_IOC_FIRST);
    cmd = _IOC_NR(command);

    if (_IOC_TYPE(command) != _IOC_TYPE(AUTOFS_DEV_IOCTL_IOC_FIRST) ||
        cmd - cmd_first >= AUTOFS_DEV_IOCTL_IOC_COUNT) {
        return -ENOTTY;
    }

    /* Copy the parameters into kernel space. */
    param = copy_dev_ioctl(user);
    if (IS_ERR(param))
        return PTR_ERR(param);

    err = validate_dev_ioctl(command, param);
    if (err)
        goto out;

    /* The validate routine above always sets the version */
    if (cmd == AUTOFS_DEV_IOCTL_VERSION_CMD)
        goto done;

    fn = lookup_dev_ioctl(cmd);
    if (!fn) {
        AUTOFS_WARN("unknown command 0x%08x", command);
        return -ENOTTY;
    }

    fp = NULL;
    sbi = NULL;

    /*
     * For obvious reasons the openmount can't have a file
     * descriptor yet. We don't take a reference to the
     * file during close to allow for immediate release.
     */
    if (cmd != AUTOFS_DEV_IOCTL_OPENMOUNT_CMD &&
        cmd != AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD) {
        fp = fget(param->ioctlfd);
        if (!fp) {
            if (cmd == AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD)
                goto cont;
            err = -EBADF;
            goto out;
        }

        if (!fp->f_op) {
            err = -ENOTTY;
            fput(fp);
            goto out;
        }

        sbi = autofs_dev_ioctl_sbi(fp);
        if (!sbi || sbi->magic != AUTOFS_SBI_MAGIC) {
            err = -EINVAL;
            fput(fp);
            goto out;
        }

        /*
         * Admin needs to be able to set the mount catatonic in
         * order to be able to perform the re-open.
         */
        if (!autofs4_oz_mode(sbi) &&
            cmd != AUTOFS_DEV_IOCTL_CATATONIC_CMD) {
            err = -EACCES;
            fput(fp);
            goto out;
        }
    }
cont:
    err = fn(fp, sbi, param);

    if (fp)
        fput(fp);
done:
    if (err >= 0 && copy_to_user(user, param, AUTOFS_DEV_IOCTL_SIZE))
        err = -EFAULT;
out:
    free_dev_ioctl(param);
    return err;
}

static long autofs_dev_ioctl(struct file *file, uint command, ulong u)
{
    int err;
    err = _autofs_dev_ioctl(command, (struct autofs_dev_ioctl __user *) u);
    return (long) err;
}

#ifdef CONFIG_COMPAT
static long autofs_dev_ioctl_compat(struct file *file, uint command, ulong u)
{
    return (long) autofs_dev_ioctl(file, command, (ulong) compat_ptr(u));
}
#else
#define autofs_dev_ioctl_compat NULL
#endif

static const struct file_operations _dev_ioctl_fops = {
    .unlocked_ioctl  = autofs_dev_ioctl,
    .compat_ioctl = autofs_dev_ioctl_compat,
    .owner   = THIS_MODULE,
    .llseek = noop_llseek,
};

static struct miscdevice _autofs_dev_ioctl_misc = {
    .minor      = AUTOFS_MINOR,
    .name       = AUTOFS_DEVICE_NAME,
    .fops       = &_dev_ioctl_fops
};

MODULE_ALIAS_MISCDEV(AUTOFS_MINOR);
MODULE_ALIAS("devname:autofs");

/* Register/deregister misc character device */
int autofs_dev_ioctl_init(void)
{
    int r;

    r = misc_register(&_autofs_dev_ioctl_misc);
    if (r) {
        AUTOFS_ERROR("misc_register failed for control device");
        return r;
    }

    return 0;
}

void autofs_dev_ioctl_exit(void)
{
    misc_deregister(&_autofs_dev_ioctl_misc);
    return;
}