fhandle.c

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#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/exportfs.h>
#include <linux/fs_struct.h>
#include <linux/fsnotify.h>
#include <linux/personality.h>
#include <asm/uaccess.h>
#include "internal.h"
#include "mount.h"

static long do_sys_name_to_handle(struct path *path,
                  struct file_handle __user *ufh,
                  int __user *mnt_id)
{
    long retval;
    struct file_handle f_handle;
    int handle_dwords, handle_bytes;
    struct file_handle *handle = NULL;

    /*
     * We need t make sure wether the file system
     * support decoding of the file handle
     */
    if (!path->dentry->d_sb->s_export_op ||
        !path->dentry->d_sb->s_export_op->fh_to_dentry)
        return -EOPNOTSUPP;

    if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
        return -EFAULT;

    if (f_handle.handle_bytes > MAX_HANDLE_SZ)
        return -EINVAL;

    handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
             GFP_KERNEL);
    if (!handle)
        return -ENOMEM;

    /* convert handle size to  multiple of sizeof(u32) */
    handle_dwords = f_handle.handle_bytes >> 2;

    /* we ask for a non connected handle */
    retval = exportfs_encode_fh(path->dentry,
                    (struct fid *)handle->f_handle,
                    &handle_dwords,  0);
    handle->handle_type = retval;
    /* convert handle size to bytes */
    handle_bytes = handle_dwords * sizeof(u32);
    handle->handle_bytes = handle_bytes;
    if ((handle->handle_bytes > f_handle.handle_bytes) ||
        (retval == 255) || (retval == -ENOSPC)) {
        /* As per old exportfs_encode_fh documentation
         * we could return ENOSPC to indicate overflow
         * But file system returned 255 always. So handle
         * both the values
         */
        /*
         * set the handle size to zero so we copy only
         * non variable part of the file_handle
         */
        handle_bytes = 0;
        retval = -EOVERFLOW;
    } else
        retval = 0;
    /* copy the mount id */
    if (copy_to_user(mnt_id, &real_mount(path->mnt)->mnt_id,
             sizeof(*mnt_id)) ||
        copy_to_user(ufh, handle,
             sizeof(struct file_handle) + handle_bytes))
        retval = -EFAULT;
    kfree(handle);
    return retval;
}

SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
        struct file_handle __user *, handle, int __user *, mnt_id,
        int, flag)
{
    struct path path;
    int lookup_flags;
    int err;

    if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
        return -EINVAL;

    lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
    if (flag & AT_EMPTY_PATH)
        lookup_flags |= LOOKUP_EMPTY;
    err = user_path_at(dfd, name, lookup_flags, &path);
    if (!err) {
        err = do_sys_name_to_handle(&path, handle, mnt_id);
        path_put(&path);
    }
    return err;
}

static struct vfsmount *get_vfsmount_from_fd(int fd)
{
    struct vfsmount *mnt;

    if (fd == AT_FDCWD) {
        struct fs_struct *fs = current->fs;
        spin_lock(&fs->lock);
        mnt = mntget(fs->pwd.mnt);
        spin_unlock(&fs->lock);
    } else {
        struct fd f = fdget(fd);
        if (!f.file)
            return ERR_PTR(-EBADF);
        mnt = mntget(f.file->f_path.mnt);
        fdput(f);
    }
    return mnt;
}

static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
{
    return 1;
}

static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
                 struct path *path)
{
    int retval = 0;
    int handle_dwords;

    path->mnt = get_vfsmount_from_fd(mountdirfd);
    if (IS_ERR(path->mnt)) {
        retval = PTR_ERR(path->mnt);
        goto out_err;
    }
    /* change the handle size to multiple of sizeof(u32) */
    handle_dwords = handle->handle_bytes >> 2;
    path->dentry = exportfs_decode_fh(path->mnt,
                      (struct fid *)handle->f_handle,
                      handle_dwords, handle->handle_type,
                      vfs_dentry_acceptable, NULL);
    if (IS_ERR(path->dentry)) {
        retval = PTR_ERR(path->dentry);
        goto out_mnt;
    }
    return 0;
out_mnt:
    mntput(path->mnt);
out_err:
    return retval;
}

static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
           struct path *path)
{
    int retval = 0;
    struct file_handle f_handle;
    struct file_handle *handle = NULL;

    /*
     * With handle we don't look at the execute bit on the
     * the directory. Ideally we would like CAP_DAC_SEARCH.
     * But we don't have that
     */
    if (!capable(CAP_DAC_READ_SEARCH)) {
        retval = -EPERM;
        goto out_err;
    }
    if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
        retval = -EFAULT;
        goto out_err;
    }
    if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
        (f_handle.handle_bytes == 0)) {
        retval = -EINVAL;
        goto out_err;
    }
    handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
             GFP_KERNEL);
    if (!handle) {
        retval = -ENOMEM;
        goto out_err;
    }
    /* copy the full handle */
    if (copy_from_user(handle, ufh,
               sizeof(struct file_handle) +
               f_handle.handle_bytes)) {
        retval = -EFAULT;
        goto out_handle;
    }

    retval = do_handle_to_path(mountdirfd, handle, path);

out_handle:
    kfree(handle);
out_err:
    return retval;
}

long do_handle_open(int mountdirfd,
            struct file_handle __user *ufh, int open_flag)
{
    long retval = 0;
    struct path path;
    struct file *file;
    int fd;

    retval = handle_to_path(mountdirfd, ufh, &path);
    if (retval)
        return retval;

    fd = get_unused_fd_flags(open_flag);
    if (fd < 0) {
        path_put(&path);
        return fd;
    }
    file = file_open_root(path.dentry, path.mnt, "", open_flag);
    if (IS_ERR(file)) {
        put_unused_fd(fd);
        retval =  PTR_ERR(file);
    } else {
        retval = fd;
        fsnotify_open(file);
        fd_install(fd, file);
    }
    path_put(&path);
    return retval;
}

SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
        struct file_handle __user *, handle,
        int, flags)
{
    long ret;

    if (force_o_largefile())
        flags |= O_LARGEFILE;

    ret = do_handle_open(mountdirfd, handle, flags);
    return ret;
}