LXR linux/fs/fhandle.c

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/syscalls.h>
   3#include <linux/slab.h>
   4#include <linux/fs.h>
   5#include <linux/file.h>
   6#include <linux/mount.h>
   7#include <linux/namei.h>
   8#include <linux/exportfs.h>
   9#include <linux/fs_struct.h>
  10#include <linux/fsnotify.h>
  11#include <linux/personality.h>
  12#include <linux/uaccess.h>
  13#include <linux/compat.h>
  14#include "internal.h"
  15#include "mount.h"
  16
  17static long do_sys_name_to_handle(struct path *path,
  18                                  struct file_handle __user *ufh,
  19                                  int __user *mnt_id)
  20{
  21        long retval;
  22        struct file_handle f_handle;
  23        int handle_dwords, handle_bytes;
  24        struct file_handle *handle = NULL;
  25
  26        /*
  27         * We need to make sure whether the file system
  28         * support decoding of the file handle
  29         */
  30        if (!path->dentry->d_sb->s_export_op ||
  31            !path->dentry->d_sb->s_export_op->fh_to_dentry)
  32                return -EOPNOTSUPP;
  33
  34        if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
  35                return -EFAULT;
  36
  37        if (f_handle.handle_bytes > MAX_HANDLE_SZ)
  38                return -EINVAL;
  39
  40        handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  41                         GFP_KERNEL);
  42        if (!handle)
  43                return -ENOMEM;
  44
  45        /* convert handle size to multiple of sizeof(u32) */
  46        handle_dwords = f_handle.handle_bytes >> 2;
  47
  48        /* we ask for a non connected handle */
  49        retval = exportfs_encode_fh(path->dentry,
  50                                    (struct fid *)handle->f_handle,
  51                                    &handle_dwords,  0);
  52        handle->handle_type = retval;
  53        /* convert handle size to bytes */
  54        handle_bytes = handle_dwords * sizeof(u32);
  55        handle->handle_bytes = handle_bytes;
  56        if ((handle->handle_bytes > f_handle.handle_bytes) ||
  57            (retval == FILEID_INVALID) || (retval == -ENOSPC)) {
  58                /* As per old exportfs_encode_fh documentation
  59                 * we could return ENOSPC to indicate overflow
  60                 * But file system returned 255 always. So handle
  61                 * both the values
  62                 */
  63                /*
  64                 * set the handle size to zero so we copy only
  65                 * non variable part of the file_handle
  66                 */
  67                handle_bytes = 0;
  68                retval = -EOVERFLOW;
  69        } else
  70                retval = 0;
  71        /* copy the mount id */
  72        if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
  73            copy_to_user(ufh, handle,
  74                         sizeof(struct file_handle) + handle_bytes))
  75                retval = -EFAULT;
  76        kfree(handle);
  77        return retval;
  78}
  79
  80/**
  81 * sys_name_to_handle_at: convert name to handle
  82 * @dfd: directory relative to which name is interpreted if not absolute
  83 * @name: name that should be converted to handle.
  84 * @handle: resulting file handle
  85 * @mnt_id: mount id of the file system containing the file
  86 * @flag: flag value to indicate whether to follow symlink or not
  87 *
  88 * @handle->handle_size indicate the space available to store the
  89 * variable part of the file handle in bytes. If there is not
  90 * enough space, the field is updated to return the minimum
  91 * value required.
  92 */
  93SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
  94                struct file_handle __user *, handle, int __user *, mnt_id,
  95                int, flag)
  96{
  97        struct path path;
  98        int lookup_flags;
  99        int err;
 100
 101        if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
 102                return -EINVAL;
 103
 104        lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
 105        if (flag & AT_EMPTY_PATH)
 106                lookup_flags |= LOOKUP_EMPTY;
 107        err = user_path_at(dfd, name, lookup_flags, &path);
 108        if (!err) {
 109                err = do_sys_name_to_handle(&path, handle, mnt_id);
 110                path_put(&path);
 111        }
 112        return err;
 113}
 114
 115static struct vfsmount *get_vfsmount_from_fd(int fd)
 116{
 117        struct vfsmount *mnt;
 118
 119        if (fd == AT_FDCWD) {
 120                struct fs_struct *fs = current->fs;
 121                spin_lock(&fs->lock);
 122                mnt = mntget(fs->pwd.mnt);
 123                spin_unlock(&fs->lock);
 124        } else {
 125                struct fd f = fdget(fd);
 126                if (!f.file)
 127                        return ERR_PTR(-EBADF);
 128                mnt = mntget(f.file->f_path.mnt);
 129                fdput(f);
 130        }
 131        return 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         * 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        *handle = f_handle;
 200        if (copy_from_user(&handle->f_handle,
 201                           &ufh->f_handle,
 202                           f_handle.handle_bytes)) {
 203                retval = -EFAULT;
 204                goto out_handle;
 205        }
 206
 207        retval = do_handle_to_path(mountdirfd, handle, path);
 208
 209out_handle:
 210        kfree(handle);
 211out_err:
 212        return retval;
 213}
 214
 215static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
 216                           int open_flag)
 217{
 218        long retval = 0;
 219        struct path path;
 220        struct file *file;
 221        int fd;
 222
 223        retval = handle_to_path(mountdirfd, ufh, &path);
 224        if (retval)
 225                return retval;
 226
 227        fd = get_unused_fd_flags(open_flag);
 228        if (fd < 0) {
 229                path_put(&path);
 230                return fd;
 231        }
 232        file = file_open_root(&path, "", open_flag, 0);
 233        if (IS_ERR(file)) {
 234                put_unused_fd(fd);
 235                retval =  PTR_ERR(file);
 236        } else {
 237                retval = fd;
 238                fsnotify_open(file);
 239                fd_install(fd, file);
 240        }
 241        path_put(&path);
 242        return retval;
 243}
 244
 245/**
 246 * sys_open_by_handle_at: Open the file handle
 247 * @mountdirfd: directory file descriptor
 248 * @handle: file handle to be opened
 249 * @flags: open flags.
 250 *
 251 * @mountdirfd indicate the directory file descriptor
 252 * of the mount point. file handle is decoded relative
 253 * to the vfsmount pointed by the @mountdirfd. @flags
 254 * value is same as the open(2) flags.
 255 */
 256SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 257                struct file_handle __user *, handle,
 258                int, flags)
 259{
 260        long ret;
 261
 262        if (force_o_largefile())
 263                flags |= O_LARGEFILE;
 264
 265        ret = do_handle_open(mountdirfd, handle, flags);
 266        return ret;
 267}
 268
 269#ifdef CONFIG_COMPAT
 270/*
 271 * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
 272 * doesn't set the O_LARGEFILE flag.
 273 */
 274COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 275                             struct file_handle __user *, handle, int, flags)
 276{
 277        return do_handle_open(mountdirfd, handle, flags);
 278}
 279#endif
 280