[gparted] Prevent crash when creating new partition on loop label (#721988)

[Mike Fleetwood <mfleetwo src gnome org>]

commit 0e253fa234a16651e4c334b9599df016e7ed0cc7
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Jan 11 15:18:01 2014 +0000

    Prevent crash when creating new partition on loop label (#721988)
    
    Write a loop partition table to a disk and then try to create a new
    partition on that disk crashes GParted.
    
    Analysis:
    
    1) Loop partition table, actually just the signature / label
       "GNU Parted Loopback 0", is written to the disk.
    2) create_partition() calls ped_disk_app_partition() to create the
       partition which, arguably erroneously, clears the loop signature.
    3) In erase_filesystem_signatures(), get_device_and_disk() fails because
       there's no longer a loop signature for libparted to recognise.  This
       leaves lp_device, lp_disk and lp_partition = NULL, but incorrectly
       overall_success = true.
    4) Overall_success = true allows the signature erasure loop to run and
       evaluate lp_device->sector_size, dereferencing a NULL pointer and
       crashing GParted.
    
    Fix erase_filesystem_signatures() to correctly handle failure from
    get_device_and_disk(), broken by this commit:
    
        246e05559d91865dd135690a62d56144f375c26b
        Clear btrfs file system super block mirror copies too (#705426)
    
    Bug #721988 - Crash when creating new partition on disk with loop label

 src/GParted_Core.cc |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/GParted_Core.cc b/src/GParted_Core.cc
index 26d7b69..1859a19 100644
--- a/src/GParted_Core.cc
+++ b/src/GParted_Core.cc
@@ -3112,7 +3112,7 @@ bool GParted_Core::filesystem_resize_disallowed( const Partition & partition )
 
 bool GParted_Core::erase_filesystem_signatures( const Partition & partition, OperationDetail & 
operationdetail )
 {
-       bool overall_success = true ;
+       bool overall_success = false ;
        operationdetail .add_child( OperationDetail(
                        String::ucompose( _("clear old file system signatures in %1"),
                                          partition .get_path() ) ) ) ;
@@ -3137,6 +3137,7 @@ bool GParted_Core::erase_filesystem_signatures( const Partition & partition, Ope
                        if ( buf )
                                memset( buf, 0, bufsize ) ;
                }
+               overall_success = device_is_open ;
        }
 
        //Erase all file system super blocks, including their signatures.  The specified