linux/fs/fhandle.c
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   1#include <linux/syscalls.h>
   2#include <linux/slab.h>
   3#include <linux/fs.h>
   4#include <linux/file.h>
   5#include <linux/mount.h>
   6#include <linux/namei.h>
   7#include <linux/exportfs.h>
   8#include <linux/fs_struct.h>
   9#include <linux/fsnotify.h>
  10#include <linux/personality.h>
  11#include <asm/uaccess.h>
  12#include "internal.h"
  13
  14static long do_sys_name_to_handle(struct path *path,
  15                                  struct file_handle __user *ufh,
  16                                  int __user *mnt_id)
  17{
  18        long retval;
  19        struct file_handle f_handle;
  20        int handle_dwords, handle_bytes;
  21        struct file_handle *handle = NULL;
  22
  23        /*
  24         * We need t make sure wether the file system
  25         * support decoding of the file handle
  26         */
  27        if (!path->mnt->mnt_sb->s_export_op ||
  28            !path->mnt->mnt_sb->s_export_op->fh_to_dentry)
  29                return -EOPNOTSUPP;
  30
  31        if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
  32                return -EFAULT;
  33
  34        if (f_handle.handle_bytes > MAX_HANDLE_SZ)
  35                return -EINVAL;
  36
  37        handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  38                         GFP_KERNEL);
  39        if (!handle)
  40                return -ENOMEM;
  41
  42        /* convert handle size to  multiple of sizeof(u32) */
  43        handle_dwords = f_handle.handle_bytes >> 2;
  44
  45        /* we ask for a non connected handle */
  46        retval = exportfs_encode_fh(path->dentry,
  47                                    (struct fid *)handle->f_handle,
  48                                    &handle_dwords,  0);
  49        handle->handle_type = retval;
  50        /* convert handle size to bytes */
  51        handle_bytes = handle_dwords * sizeof(u32);
  52        handle->handle_bytes = handle_bytes;
  53        if ((handle->handle_bytes > f_handle.handle_bytes) ||
  54            (retval == 255) || (retval == -ENOSPC)) {
  55                /* As per old exportfs_encode_fh documentation
  56                 * we could return ENOSPC to indicate overflow
  57                 * But file system returned 255 always. So handle
  58                 * both the values
  59                 */
  60                /*
  61                 * set the handle size to zero so we copy only
  62                 * non variable part of the file_handle
  63                 */
  64                handle_bytes = 0;
  65                retval = -EOVERFLOW;
  66        } else
  67                retval = 0;
  68        /* copy the mount id */
  69        if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id)) ||
  70            copy_to_user(ufh, handle,
  71                         sizeof(struct file_handle) + handle_bytes))
  72                retval = -EFAULT;
  73        kfree(handle);
  74        return retval;
  75}
  76
  77/**
  78 * sys_name_to_handle_at: convert name to handle
  79 * @dfd: directory relative to which name is interpreted if not absolute
  80 * @name: name that should be converted to handle.
  81 * @handle: resulting file handle
  82 * @mnt_id: mount id of the file system containing the file
  83 * @flag: flag value to indicate whether to follow symlink or not
  84 *
  85 * @handle->handle_size indicate the space available to store the
  86 * variable part of the file handle in bytes. If there is not
  87 * enough space, the field is updated to return the minimum
  88 * value required.
  89 */
  90SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
  91                struct file_handle __user *, handle, int __user *, mnt_id,
  92                int, flag)
  93{
  94        struct path path;
  95        int lookup_flags;
  96        int err;
  97
  98        if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
  99                return -EINVAL;
 100
 101        lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
 102        if (flag & AT_EMPTY_PATH)
 103                lookup_flags |= LOOKUP_EMPTY;
 104        err = user_path_at(dfd, name, lookup_flags, &path);
 105        if (!err) {
 106                err = do_sys_name_to_handle(&path, handle, mnt_id);
 107                path_put(&path);
 108        }
 109        return err;
 110}
 111
 112static struct vfsmount *get_vfsmount_from_fd(int fd)
 113{
 114        struct path path;
 115
 116        if (fd == AT_FDCWD) {
 117                struct fs_struct *fs = current->fs;
 118                spin_lock(&fs->lock);
 119                path = fs->pwd;
 120                mntget(path.mnt);
 121                spin_unlock(&fs->lock);
 122        } else {
 123                int fput_needed;
 124                struct file *file = fget_light(fd, &fput_needed);
 125                if (!file)
 126                        return ERR_PTR(-EBADF);
 127                path = file->f_path;
 128                mntget(path.mnt);
 129                fput_light(file, fput_needed);
 130        }
 131        return path.mnt;
 132}
 133
 134static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 135{
 136        return 1;
 137}
 138
 139static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
 140                             struct path *path)
 141{
 142        int retval = 0;
 143        int handle_dwords;
 144
 145        path->mnt = get_vfsmount_from_fd(mountdirfd);
 146        if (IS_ERR(path->mnt)) {
 147                retval = PTR_ERR(path->mnt);
 148                goto out_err;
 149        }
 150        /* change the handle size to multiple of sizeof(u32) */
 151        handle_dwords = handle->handle_bytes >> 2;
 152        path->dentry = exportfs_decode_fh(path->mnt,
 153                                          (struct fid *)handle->f_handle,
 154                                          handle_dwords, handle->handle_type,
 155                                          vfs_dentry_acceptable, NULL);
 156        if (IS_ERR(path->dentry)) {
 157                retval = PTR_ERR(path->dentry);
 158                goto out_mnt;
 159        }
 160        return 0;
 161out_mnt:
 162        mntput(path->mnt);
 163out_err:
 164        return retval;
 165}
 166
 167static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 168                   struct path *path)
 169{
 170        int retval = 0;
 171        struct file_handle f_handle;
 172        struct file_handle *handle = NULL;
 173
 174        /*
 175         * With handle we don't look at the execute bit on the
 176         * the directory. Ideally we would like CAP_DAC_SEARCH.
 177         * But we don't have that
 178         */
 179        if (!capable(CAP_DAC_READ_SEARCH)) {
 180                retval = -EPERM;
 181                goto out_err;
 182        }
 183        if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
 184                retval = -EFAULT;
 185                goto out_err;
 186        }
 187        if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
 188            (f_handle.handle_bytes == 0)) {
 189                retval = -EINVAL;
 190                goto out_err;
 191        }
 192        handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
 193                         GFP_KERNEL);
 194        if (!handle) {
 195                retval = -ENOMEM;
 196                goto out_err;
 197        }
 198        /* copy the full handle */
 199        if (copy_from_user(handle, ufh,
 200                           sizeof(struct file_handle) +
 201                           f_handle.handle_bytes)) {
 202                retval = -EFAULT;
 203                goto out_handle;
 204        }
 205
 206        retval = do_handle_to_path(mountdirfd, handle, path);
 207
 208out_handle:
 209        kfree(handle);
 210out_err:
 211        return retval;
 212}
 213
 214long do_handle_open(int mountdirfd,
 215                    struct file_handle __user *ufh, int open_flag)
 216{
 217        long retval = 0;
 218        struct path path;
 219        struct file *file;
 220        int fd;
 221
 222        retval = handle_to_path(mountdirfd, ufh, &path);
 223        if (retval)
 224                return retval;
 225
 226        fd = get_unused_fd_flags(open_flag);
 227        if (fd < 0) {
 228                path_put(&path);
 229                return fd;
 230        }
 231        file = file_open_root(path.dentry, path.mnt, "", open_flag);
 232        if (IS_ERR(file)) {
 233                put_unused_fd(fd);
 234                retval =  PTR_ERR(file);
 235        } else {
 236                retval = fd;
 237                fsnotify_open(file);
 238                fd_install(fd, file);
 239        }
 240        path_put(&path);
 241        return retval;
 242}
 243
 244/**
 245 * sys_open_by_handle_at: Open the file handle
 246 * @mountdirfd: directory file descriptor
 247 * @handle: file handle to be opened
 248 * @flag: open flags.
 249 *
 250 * @mountdirfd indicate the directory file descriptor
 251 * of the mount point. file handle is decoded relative
 252 * to the vfsmount pointed by the @mountdirfd. @flags
 253 * value is same as the open(2) flags.
 254 */
 255SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 256                struct file_handle __user *, handle,
 257                int, flags)
 258{
 259        long ret;
 260
 261        if (force_o_largefile())
 262                flags |= O_LARGEFILE;
 263
 264        ret = do_handle_open(mountdirfd, handle, flags);
 265        return ret;
 266}
 267
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