vfs: Add name to file handle conversion support

[mirror_ubuntu-bionic-kernel.git] / fs / fhandle.c

diff --git a/fs/fhandle.c b/fs/fhandle.c
new file mode 100644 (file)
index 0000000..9f79e74
--- /dev/null
+++ b/fs/fhandle.c
@@ -0,0 +1,107 @@
+#include <linux/syscalls.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/exportfs.h>
+#include <asm/uaccess.h>
+#include "internal.h"
+
+static long do_sys_name_to_handle(struct path *path,
+                                 struct file_handle __user *ufh,
+                                 int __user *mnt_id)
+{
+       long retval;
+       struct file_handle f_handle;
+       int handle_dwords, handle_bytes;
+       struct file_handle *handle = NULL;
+
+       /*
+        * We need t make sure wether the file system
+        * support decoding of the file handle
+        */
+       if (!path->mnt->mnt_sb->s_export_op ||
+           !path->mnt->mnt_sb->s_export_op->fh_to_dentry)
+               return -EOPNOTSUPP;
+
+       if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
+               return -EFAULT;
+
+       if (f_handle.handle_bytes > MAX_HANDLE_SZ)
+               return -EINVAL;
+
+       handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
+                        GFP_KERNEL);
+       if (!handle)
+               return -ENOMEM;
+
+       /* convert handle size to  multiple of sizeof(u32) */
+       handle_dwords = f_handle.handle_bytes >> 2;
+
+       /* we ask for a non connected handle */
+       retval = exportfs_encode_fh(path->dentry,
+                                   (struct fid *)handle->f_handle,
+                                   &handle_dwords,  0);
+       handle->handle_type = retval;
+       /* convert handle size to bytes */
+       handle_bytes = handle_dwords * sizeof(u32);
+       handle->handle_bytes = handle_bytes;
+       if ((handle->handle_bytes > f_handle.handle_bytes) ||
+           (retval == 255) || (retval == -ENOSPC)) {
+               /* As per old exportfs_encode_fh documentation
+                * we could return ENOSPC to indicate overflow
+                * But file system returned 255 always. So handle
+                * both the values
+                */
+               /*
+                * set the handle size to zero so we copy only
+                * non variable part of the file_handle
+                */
+               handle_bytes = 0;
+               retval = -EOVERFLOW;
+       } else
+               retval = 0;
+       /* copy the mount id */
+       if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id)) ||
+           copy_to_user(ufh, handle,
+                        sizeof(struct file_handle) + handle_bytes))
+               retval = -EFAULT;
+       kfree(handle);
+       return retval;
+}
+
+/**
+ * sys_name_to_handle_at: convert name to handle
+ * @dfd: directory relative to which name is interpreted if not absolute
+ * @name: name that should be converted to handle.
+ * @handle: resulting file handle
+ * @mnt_id: mount id of the file system containing the file
+ * @flag: flag value to indicate whether to follow symlink or not
+ *
+ * @handle->handle_size indicate the space available to store the
+ * variable part of the file handle in bytes. If there is not
+ * enough space, the field is updated to return the minimum
+ * value required.
+ */
+SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
+               struct file_handle __user *, handle, int __user *, mnt_id,
+               int, flag)
+{
+       struct path path;
+       int lookup_flags;
+       int err;
+
+       if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
+               return -EINVAL;
+
+       lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
+       if (flag & AT_EMPTY_PATH)
+               lookup_flags |= LOOKUP_EMPTY;
+       err = user_path_at(dfd, name, lookup_flags, &path);
+       if (!err) {
+               err = do_sys_name_to_handle(&path, handle, mnt_id);
+               path_put(&path);
+       }
+       return err;
+}