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