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
  17 static 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  */
  93 SYSCALL_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
 115 static 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
 134 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 135 {
 136         return 1;
 137 }
 138
 139 static 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;
 161 out_mnt:
 162         mntput(path->mnt);
 163 out_err:
 164         return retval;
 165 }
 166
 167 static 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         *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
 209 out_handle:
 210         kfree(handle);
 211 out_err:
 212         return retval;
 213 }
 214
 215 static 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.dentry, path.mnt, "", 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  */
 256 SYSCALL_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  */
 274 COMPAT_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