[gvfs] daemon: Avoid overflowing when querying for filesystem info

[Ondrej Holy <oholy src gnome org>]

commit cdaa10cef32ed935a783b2700675be0af3c9542e
Author: Michael Terry <mike mterry name>
Date:   Sun Aug 20 00:06:47 2017 -0400

    daemon: Avoid overflowing when querying for filesystem info
    
    Filesystem sizes can be large and in danger of overflowing. Guard
    against that possibility in the dav and fuse FS query code.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786177

 client/gvfsfusedaemon.c |    5 ++++-
 daemon/gvfsbackenddav.c |    2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/client/gvfsfusedaemon.c b/client/gvfsfusedaemon.c
index 5a7767c..ff5641a 100644
--- a/client/gvfsfusedaemon.c
+++ b/client/gvfsfusedaemon.c
@@ -645,7 +645,10 @@ vfs_statfs (const gchar *path, struct statvfs *stbuf)
       if (file_info)
         {
           if (g_file_info_has_attribute (file_info, G_FILE_ATTRIBUTE_FILESYSTEM_SIZE))
-            stbuf->f_blocks = (g_file_info_get_attribute_uint64 (file_info, 
G_FILE_ATTRIBUTE_FILESYSTEM_SIZE) + 4096 - 1) / 4096;
+            {
+              guint64 size = g_file_info_get_attribute_uint64 (file_info, G_FILE_ATTRIBUTE_FILESYSTEM_SIZE);
+              stbuf->f_blocks = (size > 0) ? ((size - 1) / 4096 + 1) : 0;
+            }
           if (g_file_info_has_attribute (file_info, G_FILE_ATTRIBUTE_FILESYSTEM_FREE))
             stbuf->f_bfree = stbuf->f_bavail = g_file_info_get_attribute_uint64 (file_info, 
G_FILE_ATTRIBUTE_FILESYSTEM_FREE) / 4096;
 
diff --git a/daemon/gvfsbackenddav.c b/daemon/gvfsbackenddav.c
index e8a3903..7ff7b91 100644
--- a/daemon/gvfsbackenddav.c
+++ b/daemon/gvfsbackenddav.c
@@ -1202,7 +1202,7 @@ ms_response_to_fs_info (MsResponse *response,
       g_file_info_set_attribute_uint64 (info,
                                         G_FILE_ATTRIBUTE_FILESYSTEM_FREE,
                                         bytes_avail);
-      if (have_bytes_used)
+      if (have_bytes_used && G_MAXUINT64 - bytes_avail >= bytes_used)
         g_file_info_set_attribute_uint64 (info,
                                          G_FILE_ATTRIBUTE_FILESYSTEM_SIZE,
                                          bytes_avail + bytes_used);