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