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#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 t make sure wether 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 == 255) || (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 path path;
 117
 118        if (fd == AT_FDCWD) {
 119                struct fs_struct *fs = current->fs;
 120                spin_lock(&fs->lock);
 121                path = fs->pwd;
 122                mntget(path.mnt);
 123                spin_unlock(&fs->lock);
 124        } else {
 125                int fput_needed;
 126                struct file *file = fget_light(fd, &fput_needed);
 127                if (!file)
 128                        return ERR_PTR(-EBADF);
 129                path = file->f_path;
 130                mntget(path.mnt);
 131                fput_light(file, fput_needed);
 132        }
 133        return path.mnt;
 134}
 135
 136static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 137{
 138        return 1;
 139}
 140
 141static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
 142                             struct path *path)
 143{
 144        int retval = 0;
 145        int handle_dwords;
 146
 147        path->mnt = get_vfsmount_from_fd(mountdirfd);
 148        if (IS_ERR(path->mnt)) {
 149                retval = PTR_ERR(path->mnt);
 150                goto out_err;
 151        }
 152        /* change the handle size to multiple of sizeof(u32) */
 153        handle_dwords = handle->handle_bytes >> 2;
 154        path->dentry = exportfs_decode_fh(path->mnt,
 155                                          (struct fid *)handle->f_handle,
 156                                          handle_dwords, handle->handle_type,
 157                                          vfs_dentry_acceptable, NULL);
 158        if (IS_ERR(path->dentry)) {
 159                retval = PTR_ERR(path->dentry);
 160                goto out_mnt;
 161        }
 162        return 0;
 163out_mnt:
 164        mntput(path->mnt);
 165out_err:
 166        return retval;
 167}
 168
 169static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 170                   struct path *path)
 171{
 172        int retval = 0;
 173        struct file_handle f_handle;
 174        struct file_handle *handle = NULL;
 175
 176        /*
 177         * With handle we don't look at the execute bit on the
 178         * the directory. Ideally we would like CAP_DAC_SEARCH.
 179         * But we don't have that
 180         */
 181        if (!capable(CAP_DAC_READ_SEARCH)) {
 182                retval = -EPERM;
 183                goto out_err;
 184        }
 185        if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
 186                retval = -EFAULT;
 187                goto out_err;
 188        }
 189        if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
 190            (f_handle.handle_bytes == 0)) {
 191                retval = -EINVAL;
 192                goto out_err;
 193        }
 194        handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
 195                         GFP_KERNEL);
 196        if (!handle) {
 197                retval = -ENOMEM;
 198                goto out_err;
 199        }
 200        /* copy the full handle */
 201        if (copy_from_user(handle, ufh,
 202                           sizeof(struct file_handle) +
 203                           f_handle.handle_bytes)) {
 204                retval = -EFAULT;
 205                goto out_handle;
 206        }
 207
 208        retval = do_handle_to_path(mountdirfd, handle, path);
 209
 210out_handle:
 211        kfree(handle);
 212out_err:
 213        return retval;
 214}
 215
 216long do_handle_open(int mountdirfd,
 217                    struct file_handle __user *ufh, int open_flag)
 218{
 219        long retval = 0;
 220        struct path path;
 221        struct file *file;
 222        int fd;
 223
 224        retval = handle_to_path(mountdirfd, ufh, &path);
 225        if (retval)
 226                return retval;
 227
 228        fd = get_unused_fd_flags(open_flag);
 229        if (fd < 0) {
 230                path_put(&path);
 231                return fd;
 232        }
 233        file = file_open_root(path.dentry, path.mnt, "", open_flag);
 234        if (IS_ERR(file)) {
 235                put_unused_fd(fd);
 236                retval =  PTR_ERR(file);
 237        } else {
 238                retval = fd;
 239                fsnotify_open(file);
 240                fd_install(fd, file);
 241        }
 242        path_put(&path);
 243        return retval;
 244}
 245
 246/**
 247 * sys_open_by_handle_at: Open the file handle
 248 * @mountdirfd: directory file descriptor
 249 * @handle: file handle to be opened
 250 * @flag: open flags.
 251 *
 252 * @mountdirfd indicate the directory file descriptor
 253 * of the mount point. file handle is decoded relative
 254 * to the vfsmount pointed by the @mountdirfd. @flags
 255 * value is same as the open(2) flags.
 256 */
 257SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 258                struct file_handle __user *, handle,
 259                int, flags)
 260{
 261        long ret;
 262
 263        if (force_o_largefile())
 264                flags |= O_LARGEFILE;
 265
 266        ret = do_handle_open(mountdirfd, handle, flags);
 267        return ret;
 268}
 269
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