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 #include "mount.h"
  14
  15 static long do_sys_name_to_handle(struct path *path,
  16                                   struct file_handle __user *ufh,
  17                                   int __user *mnt_id)
  18 {
  19         long retval;
  20         struct file_handle f_handle;
  21         int handle_dwords, handle_bytes;
  22         struct file_handle *handle = NULL;
  23
  24         /*
  25          * We need to make sure whether the file system
  26          * support decoding of the file handle
  27          */
  28         if (!path->dentry->d_sb->s_export_op ||
  29             !path->dentry->d_sb->s_export_op->fh_to_dentry)
  30                 return -EOPNOTSUPP;
  31
  32         if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
  33                 return -EFAULT;
  34
  35         if (f_handle.handle_bytes > MAX_HANDLE_SZ)
  36                 return -EINVAL;
  37
  38         handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  39                          GFP_KERNEL);
  40         if (!handle)
  41                 return -ENOMEM;
  42
  43         /* convert handle size to multiple of sizeof(u32) */
  44         handle_dwords = f_handle.handle_bytes >> 2;
  45
  46         /* we ask for a non connected handle */
  47         retval = exportfs_encode_fh(path->dentry,
  48                                     (struct fid *)handle->f_handle,
  49                                     &handle_dwords,  0);
  50         handle->handle_type = retval;
  51         /* convert handle size to bytes */
  52         handle_bytes = handle_dwords * sizeof(u32);
  53         handle->handle_bytes = handle_bytes;
  54         if ((handle->handle_bytes > f_handle.handle_bytes) ||
  55             (retval == FILEID_INVALID) || (retval == -ENOSPC)) {
  56                 /* As per old exportfs_encode_fh documentation
  57                  * we could return ENOSPC to indicate overflow
  58                  * But file system returned 255 always. So handle
  59                  * both the values
  60                  */
  61                 /*
  62                  * set the handle size to zero so we copy only
  63                  * non variable part of the file_handle
  64                  */
  65                 handle_bytes = 0;
  66                 retval = -EOVERFLOW;
  67         } else
  68                 retval = 0;
  69         /* copy the mount id */
  70         if (copy_to_user(mnt_id, &real_mount(path->mnt)->mnt_id,
  71                          sizeof(*mnt_id)) ||
  72             copy_to_user(ufh, handle,
  73                          sizeof(struct file_handle) + handle_bytes))
  74                 retval = -EFAULT;
  75         kfree(handle);
  76         return retval;
  77 }
  78
  79 /**
  80  * sys_name_to_handle_at: convert name to handle
  81  * @dfd: directory relative to which name is interpreted if not absolute
  82  * @name: name that should be converted to handle.
  83  * @handle: resulting file handle
  84  * @mnt_id: mount id of the file system containing the file
  85  * @flag: flag value to indicate whether to follow symlink or not
  86  *
  87  * @handle->handle_size indicate the space available to store the
  88  * variable part of the file handle in bytes. If there is not
  89  * enough space, the field is updated to return the minimum
  90  * value required.
  91  */
  92 SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
  93                 struct file_handle __user *, handle, int __user *, mnt_id,
  94                 int, flag)
  95 {
  96         struct path path;
  97         int lookup_flags;
  98         int err;
  99
 100         if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
 101                 return -EINVAL;
 102
 103         lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
 104         if (flag & AT_EMPTY_PATH)
 105                 lookup_flags |= LOOKUP_EMPTY;
 106         err = user_path_at(dfd, name, lookup_flags, &path);
 107         if (!err) {
 108                 err = do_sys_name_to_handle(&path, handle, mnt_id);
 109                 path_put(&path);
 110         }
 111         return err;
 112 }
 113
 114 static struct vfsmount *get_vfsmount_from_fd(int fd)
 115 {
 116         struct vfsmount *mnt;
 117
 118         if (fd == AT_FDCWD) {
 119                 struct fs_struct *fs = current->fs;
 120                 spin_lock(&fs->lock);
 121                 mnt = mntget(fs->pwd.mnt);
 122                 spin_unlock(&fs->lock);
 123         } else {
 124                 struct fd f = fdget(fd);
 125                 if (!f.file)
 126                         return ERR_PTR(-EBADF);
 127                 mnt = mntget(f.file->f_path.mnt);
 128                 fdput(f);
 129         }
 130         return 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         *handle = f_handle;
 199         if (copy_from_user(&handle->f_handle,
 200                            &ufh->f_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, 0);
 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 }