LXR linux/fs/fhandle.c

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