fs/fhandle.c

   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 <asm/uaccess.h>
  11 #include "internal.h"
  12
  13 static long do_sys_name_to_handle(struct path *path,
  14                                   struct file_handle __user *ufh,
  15                                   int __user *mnt_id)
  16 {
  17         long retval;
  18         struct file_handle f_handle;
  19         int handle_dwords, handle_bytes;
  20         struct file_handle *handle = NULL;
  21
  22         /*
  23          * We need t make sure wether the file system
  24          * support decoding of the file handle
  25          */
  26         if (!path->mnt->mnt_sb->s_export_op ||
  27             !path->mnt->mnt_sb->s_export_op->fh_to_dentry)
  28                 return -EOPNOTSUPP;
  29
  30         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
  31                 return -EFAULT;
  32
  33         if (f_handle.handle_bytes > MAX_HANDLE_SZ)
  34                 return -EINVAL;
  35
  36         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  37                          GFP_KERNEL);
  38         if (!handle)
  39                 return -ENOMEM;
  40
  41         /* convert handle size to  multiple of sizeof(u32) */
  42         handle_dwords = f_handle.handle_bytes >> 2;
  43
  44         /* we ask for a non connected handle */
  45         retval = exportfs_encode_fh(path->dentry,
  46                                     (struct fid *)handle->f_handle,
  47                                     &handle_dwords,  0);
  48         handle->handle_type = retval;
  49         /* convert handle size to bytes */
  50         handle_bytes = handle_dwords * sizeof(u32);
  51         handle->handle_bytes = handle_bytes;
  52         if ((handle->handle_bytes > f_handle.handle_bytes) ||
  53             (retval == 255) || (retval == -ENOSPC)) {
  54                 /* As per old exportfs_encode_fh documentation
  55                  * we could return ENOSPC to indicate overflow
  56                  * But file system returned 255 always. So handle
  57                  * both the values
  58                  */
  59                 /*
  60                  * set the handle size to zero so we copy only
  61                  * non variable part of the file_handle
  62                  */
  63                 handle_bytes = 0;
  64                 retval = -EOVERFLOW;
  65         } else
  66                 retval = 0;
  67         /* copy the mount id */
  68         if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id)) ||
  69             copy_to_user(ufh, handle,
  70                          sizeof(struct file_handle) + handle_bytes))
  71                 retval = -EFAULT;
  72         kfree(handle);
  73         return retval;
  74 }
  75
  76 /**
  77  * sys_name_to_handle_at: convert name to handle
  78  * @dfd: directory relative to which name is interpreted if not absolute
  79  * @name: name that should be converted to handle.
  80  * @handle: resulting file handle
  81  * @mnt_id: mount id of the file system containing the file
  82  * @flag: flag value to indicate whether to follow symlink or not
  83  *
  84  * @handle->handle_size indicate the space available to store the
  85  * variable part of the file handle in bytes. If there is not
  86  * enough space, the field is updated to return the minimum
  87  * value required.
  88  */
  89 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
  90                 struct file_handle __user *, handle, int __user *, mnt_id,
  91                 int, flag)
  92 {
  93         struct path path;
  94         int lookup_flags;
  95         int err;
  96
  97         if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
  98                 return -EINVAL;
  99
 100         lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
 101         if (flag & AT_EMPTY_PATH)
 102                 lookup_flags |= LOOKUP_EMPTY;
 103         err = user_path_at(dfd, name, lookup_flags, &path);
 104         if (!err) {
 105                 err = do_sys_name_to_handle(&path, handle, mnt_id);
 106                 path_put(&path);
 107         }
 108         return err;
 109 }
 110
 111 static struct vfsmount *get_vfsmount_from_fd(int fd)
 112 {
 113         struct path path;
 114
 115         if (fd == AT_FDCWD) {
 116                 struct fs_struct *fs = current->fs;
 117                 spin_lock(&fs->lock);
 118                 path = fs->pwd;
 119                 mntget(path.mnt);
 120                 spin_unlock(&fs->lock);
 121         } else {
 122                 int fput_needed;
 123                 struct file *file = fget_light(fd, &fput_needed);
 124                 if (!file)
 125                         return ERR_PTR(-EBADF);
 126                 path = file->f_path;
 127                 mntget(path.mnt);
 128                 fput_light(file, fput_needed);
 129         }
 130         return path.mnt;
 131 }
 132
 133 static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
 134 {
 135         return 1;
 136 }
 137
 138 static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
 139                              struct path *path)
 140 {
 141         int retval = 0;
 142         int handle_dwords;
 143
 144         path->mnt = get_vfsmount_from_fd(mountdirfd);
 145         if (IS_ERR(path->mnt)) {
 146                 retval = PTR_ERR(path->mnt);
 147                 goto out_err;
 148         }
 149         /* change the handle size to multiple of sizeof(u32) */
 150         handle_dwords = handle->handle_bytes >> 2;
 151         path->dentry = exportfs_decode_fh(path->mnt,
 152                                           (struct fid *)handle->f_handle,
 153                                           handle_dwords, handle->handle_type,
 154                                           vfs_dentry_acceptable, NULL);
 155         if (IS_ERR(path->dentry)) {
 156                 retval = PTR_ERR(path->dentry);
 157                 goto out_mnt;
 158         }
 159         return 0;
 160 out_mnt:
 161         mntput(path->mnt);
 162 out_err:
 163         return retval;
 164 }
 165
 166 static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 167                    struct path *path)
 168 {
 169         int retval = 0;
 170         struct file_handle f_handle;
 171         struct file_handle *handle = NULL;
 172
 173         /*
 174          * With handle we don't look at the execute bit on the
 175          * the directory. Ideally we would like CAP_DAC_SEARCH.
 176          * But we don't have that
 177          */
 178         if (!capable(CAP_DAC_READ_SEARCH)) {
 179                 retval = -EPERM;
 180                 goto out_err;
 181         }
 182         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
 183                 retval = -EFAULT;
 184                 goto out_err;
 185         }
 186         if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
 187             (f_handle.handle_bytes == 0)) {
 188                 retval = -EINVAL;
 189                 goto out_err;
 190         }
 191         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
 192                          GFP_KERNEL);
 193         if (!handle) {
 194                 retval = -ENOMEM;
 195                 goto out_err;
 196         }
 197         /* copy the full handle */
 198         if (copy_from_user(handle, ufh,
 199                            sizeof(struct file_handle) +
 200                            f_handle.handle_bytes)) {
 201                 retval = -EFAULT;
 202                 goto out_handle;
 203         }
 204
 205         retval = do_handle_to_path(mountdirfd, handle, path);
 206
 207 out_handle:
 208         kfree(handle);
 209 out_err:
 210         return retval;
 211 }
 212
 213 long do_handle_open(int mountdirfd,
 214                     struct file_handle __user *ufh, int open_flag)
 215 {
 216         long retval = 0;
 217         struct path path;
 218         struct file *file;
 219         int fd;
 220
 221         retval = handle_to_path(mountdirfd, ufh, &path);
 222         if (retval)
 223                 return retval;
 224
 225         fd = get_unused_fd_flags(open_flag);
 226         if (fd < 0) {
 227                 path_put(&path);
 228                 return fd;
 229         }
 230         file = file_open_root(path.dentry, path.mnt, "", open_flag);
 231         if (IS_ERR(file)) {
 232                 put_unused_fd(fd);
 233                 retval =  PTR_ERR(file);
 234         } else {
 235                 retval = fd;
 236                 fsnotify_open(file);
 237                 fd_install(fd, file);
 238         }
 239         path_put(&path);
 240         return retval;
 241 }
 242
 243 /**
 244  * sys_open_by_handle_at: Open the file handle
 245  * @mountdirfd: directory file descriptor
 246  * @handle: file handle to be opened
 247  * @flag: open flags.
 248  *
 249  * @mountdirfd indicate the directory file descriptor
 250  * of the mount point. file handle is decoded relative
 251  * to the vfsmount pointed by the @mountdirfd. @flags
 252  * value is same as the open(2) flags.
 253  */
 254 SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
 255                 struct file_handle __user *, handle,
 256                 int, flags)
 257 {
 258         long ret;
 259
 260         if (force_o_largefile())
 261                 flags |= O_LARGEFILE;
 262
 263         ret = do_handle_open(mountdirfd, handle, flags);
 264         return ret;
 265 }