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(const struct path *path,
  18                                   struct file_handle __user *ufh,
  19                                   int __user *mnt_id, int fh_flags)
  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 support decoding of
  28          * the file handle if decodeable file handle was requested.
  29          * Otherwise, even empty export_operations are sufficient to opt-in
  30          * to encoding FIDs.
  31          */
  32         if (!path->dentry->d_sb->s_export_op ||
  33             (!(fh_flags & EXPORT_FH_FID) &&
  34              !path->dentry->d_sb->s_export_op->fh_to_dentry))
  35                 return -EOPNOTSUPP;
  36
  37         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
  38                 return -EFAULT;
  39
  40         if (f_handle.handle_bytes > MAX_HANDLE_SZ)
  41                 return -EINVAL;
  42
  43         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  44                          GFP_KERNEL);
  45         if (!handle)
  46                 return -ENOMEM;
  47
  48         /* convert handle size to multiple of sizeof(u32) */
  49         handle_dwords = f_handle.handle_bytes >> 2;
  50
  51         /* we ask for a non connectable maybe decodeable file handle */
  52         retval = exportfs_encode_fh(path->dentry,
  53                                     (struct fid *)handle->f_handle,
  54                                     &handle_dwords, fh_flags);
  55         handle->handle_type = retval;
  56         /* convert handle size to bytes */
  57         handle_bytes = handle_dwords * sizeof(u32);
  58         handle->handle_bytes = handle_bytes;
  59         if ((handle->handle_bytes > f_handle.handle_bytes) ||
  60             (retval == FILEID_INVALID) || (retval < 0)) {
  61                 /* As per old exportfs_encode_fh documentation
  62                  * we could return ENOSPC to indicate overflow
  63                  * But file system returned 255 always. So handle
  64                  * both the values
  65                  */
  66                 if (retval == FILEID_INVALID || retval == -ENOSPC)
  67                         retval = -EOVERFLOW;
  68                 /*
  69                  * set the handle size to zero so we copy only
  70                  * non variable part of the file_handle
  71                  */
  72                 handle_bytes = 0;
  73         } else
  74                 retval = 0;
  75         /* copy the mount id */
  76         if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
  77             copy_to_user(ufh, handle,
  78                          sizeof(struct file_handle) + handle_bytes))
  79                 retval = -EFAULT;
  80         kfree(handle);
  81         return retval;
  82 }
  83
  84 /**
  85  * sys_name_to_handle_at: convert name to handle
  86  * @dfd: directory relative to which name is interpreted if not absolute
  87  * @name: name that should be converted to handle.
  88  * @handle: resulting file handle
  89  * @mnt_id: mount id of the file system containing the file
  90  * @flag: flag value to indicate whether to follow symlink or not
  91  *        and whether a decodable file handle is required.
  92  *
  93  * @handle->handle_size indicate the space available to store the
  94  * variable part of the file handle in bytes. If there is not
  95  * enough space, the field is updated to return the minimum
  96  * value required.
  97  */
  98 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
  99                 struct file_handle __user *, handle, int __user *, mnt_id,
 100                 int, flag)
 101 {
 102         struct path path;
 103         int lookup_flags;
 104         int fh_flags;
 105         int err;
 106
 107         if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID))
 108                 return -EINVAL;
 109
 110         lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
 111         fh_flags = (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0;
 112         if (flag & AT_EMPTY_PATH)
 113                 lookup_flags |= LOOKUP_EMPTY;
 114         err = user_path_at(dfd, name, lookup_flags, &path);
 115         if (!err) {
 116                 err = do_sys_name_to_handle(&path, handle, mnt_id, fh_flags);
 117                 path_put(&path);
 118         }
 119         return err;
 120 }
 121
 122 static struct vfsmount *get_vfsmount_from_fd(int fd)
 123 {
 124         struct vfsmount *mnt;
 125
 126         if (fd == AT_FDCWD) {
 127                 struct fs_struct *fs = current->fs;
 128                 spin_lock(&fs->lock);
 129                 mnt = mntget(fs->pwd.mnt);
 130                 spin_unlock(&fs->lock);
 131         } else {
 132                 struct fd f = fdget(fd);
 133                 if (!f.file)
 134                         return ERR_PTR(-EBADF);
 135                 mnt = mntget(f.file->f_path.mnt);
 136                 fdput(f);
 137         }
 138         return mnt;
 139 }
 140
 141 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 142 {
 143         return 1;
 144 }
 145
 146 static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
 147                              struct path *path)
 148 {
 149         int retval = 0;
 150         int handle_dwords;
 151
 152         path->mnt = get_vfsmount_from_fd(mountdirfd);
 153         if (IS_ERR(path->mnt)) {
 154                 retval = PTR_ERR(path->mnt);
 155                 goto out_err;
 156         }
 157         /* change the handle size to multiple of sizeof(u32) */
 158         handle_dwords = handle->handle_bytes >> 2;
 159         path->dentry = exportfs_decode_fh(path->mnt,
 160                                           (struct fid *)handle->f_handle,
 161                                           handle_dwords, handle->handle_type,
 162                                           vfs_dentry_acceptable, NULL);
 163         if (IS_ERR(path->dentry)) {
 164                 retval = PTR_ERR(path->dentry);
 165                 goto out_mnt;
 166         }
 167         return 0;
 168 out_mnt:
 169         mntput(path->mnt);
 170 out_err:
 171         return retval;
 172 }
 173
 174 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 175                    struct path *path)
 176 {
 177         int retval = 0;
 178         struct file_handle f_handle;
 179         struct file_handle *handle = NULL;
 180
 181         /*
 182          * With handle we don't look at the execute bit on the
 183          * directory. Ideally we would like CAP_DAC_SEARCH.
 184          * But we don't have that
 185          */
 186         if (!capable(CAP_DAC_READ_SEARCH)) {
 187                 retval = -EPERM;
 188                 goto out_err;
 189         }
 190         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
 191                 retval = -EFAULT;
 192                 goto out_err;
 193         }
 194         if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
 195             (f_handle.handle_bytes == 0)) {
 196                 retval = -EINVAL;
 197                 goto out_err;
 198         }
 199         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
 200                          GFP_KERNEL);
 201         if (!handle) {
 202                 retval = -ENOMEM;
 203                 goto out_err;
 204         }
 205         /* copy the full handle */
 206         *handle = f_handle;
 207         if (copy_from_user(&handle->f_handle,
 208                            &ufh->f_handle,
 209                            f_handle.handle_bytes)) {
 210                 retval = -EFAULT;
 211                 goto out_handle;
 212         }
 213
 214         retval = do_handle_to_path(mountdirfd, handle, path);
 215
 216 out_handle:
 217         kfree(handle);
 218 out_err:
 219         return retval;
 220 }
 221
 222 static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
 223                            int open_flag)
 224 {
 225         long retval = 0;
 226         struct path path;
 227         struct file *file;
 228         int fd;
 229
 230         retval = handle_to_path(mountdirfd, ufh, &path);
 231         if (retval)
 232                 return retval;
 233
 234         fd = get_unused_fd_flags(open_flag);
 235         if (fd < 0) {
 236                 path_put(&path);
 237                 return fd;
 238         }
 239         file = file_open_root(&path, "", open_flag, 0);
 240         if (IS_ERR(file)) {
 241                 put_unused_fd(fd);
 242                 retval =  PTR_ERR(file);
 243         } else {
 244                 retval = fd;
 245                 fd_install(fd, file);
 246         }
 247         path_put(&path);
 248         return retval;
 249 }
 250
 251 /**
 252  * sys_open_by_handle_at: Open the file handle
 253  * @mountdirfd: directory file descriptor
 254  * @handle: file handle to be opened
 255  * @flags: open flags.
 256  *
 257  * @mountdirfd indicate the directory file descriptor
 258  * of the mount point. file handle is decoded relative
 259  * to the vfsmount pointed by the @mountdirfd. @flags
 260  * value is same as the open(2) flags.
 261  */
 262 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 263                 struct file_handle __user *, handle,
 264                 int, flags)
 265 {
 266         long ret;
 267
 268         if (force_o_largefile())
 269                 flags |= O_LARGEFILE;
 270
 271         ret = do_handle_open(mountdirfd, handle, flags);
 272         return ret;
 273 }
 274
 275 #ifdef CONFIG_COMPAT
 276 /*
 277  * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
 278  * doesn't set the O_LARGEFILE flag.
 279  */
 280 COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 281                              struct file_handle __user *, handle, int, flags)
 282 {
 283         return do_handle_open(mountdirfd, handle, flags);
 284 }
 285 #endif