cifs: fix build_unc_path_to_root to account for a prefixpath

Regression introduced by commit f87d39d9513.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastryyy@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -2855,19 +2855,28 @@ cifs_cleanup_volume_info(struct smb_vol **pvolume_info)
 /* build_path_to_root returns full path to root when
  * we do not have an exiting connection (tcon) */
 static char *
-build_unc_path_to_root(const struct smb_vol *volume_info,
+build_unc_path_to_root(const struct smb_vol *vol,
 		const struct cifs_sb_info *cifs_sb)
 {
-	char *full_path;
+	char *full_path, *pos;
+	unsigned int pplen = vol->prepath ? strlen(vol->prepath) : 0;
+	unsigned int unc_len = strnlen(vol->UNC, MAX_TREE_SIZE + 1);
 
-	int unc_len = strnlen(volume_info->UNC, MAX_TREE_SIZE + 1);
-	full_path = kmalloc(unc_len + 1, GFP_KERNEL);
+	full_path = kmalloc(unc_len + pplen + 1, GFP_KERNEL);
 	if (full_path == NULL)
 		return ERR_PTR(-ENOMEM);
 
-	strncpy(full_path, volume_info->UNC, unc_len);
-	full_path[unc_len] = 0; /* add trailing null */
+	strncpy(full_path, vol->UNC, unc_len);
+	pos = full_path + unc_len;
+
+	if (pplen) {
+		strncpy(pos, vol->prepath, pplen);
+		pos += pplen;
+	}
+
+	*pos = '\0'; /* add trailing null */
 	convert_delimiter(full_path, CIFS_DIR_SEP(cifs_sb));
+	cFYI(1, "%s: full_path=%s", __func__, full_path);
 	return full_path;
 }