[gparted] Fix crash reading NTFS usage when there is no /dev/PTN entry (#764658)

[Curtis Gedak <gedakc src gnome org>]

commit 366152e4499fce4560e9889489fca8b42c5f67d0
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Mon Apr 4 16:28:16 2016 +0100

    Fix crash reading NTFS usage when there is no /dev/PTN entry (#764658)
    
    On a 64-bit distribution, with an NTFS file system in a partition
    without a /dev entry then GParted will crash when attempting to read
    the file system usage.  Not having a /dev entry for the partition is
    rare and only known to occur for the disk devices used within Fake RAID
    (dmraid) arrays, and then only on Ubuntu 12.04 LTS.  Other/newer
    distributions do create /dev entries for partitions found on disk
    devices within Fake RAID arrays.
    
    Create mirror Fake RAID array:
        # dmraid -f isw -C MyArray --type 1 --disk /dev/sdc,/dev/sdd
        # dmraid -ay
    
    Create NTFS partition on the Fake RAID array.  On refresh GParted
    crashes:
        # ./gpartedbin
        (gpartedbin:590): glibmm-ERROR **:
        unhandled exception (type std::exception) in signal handler:
        what: basic_string::assign
    
    Without a /dev/sdc1 device entry the ntfsresize command reports this:
        # ntfsresize --info --force --no-progress-bar /dev/sdc1
        ntfsresize v2015.3.14 (libntfs-3g)
        ERROR(2): Failed to check '/dev/sdc1' mount state: No such file or directory
        Probably /etc/mtab is missing. It's too risky to continue. You might try
        an another Linux distro.
    
    The problem code in ntfs::set_used_sectors():
        145         index = output.find( "Cluster size" );
        146         if ( index == output.npos ||
        147              sscanf( output.substr( index ).c_str(), "Cluster size       : %Ld", &S ) != 1 )
    As "Cluster size" did not exist in the output find() returned the not
    found token of string::npos [1], which in a 64-bit environment is
    represented by 2^64-1 [2].  However it was saved in the variable index
    of type unsigned integer, which is only a 32-bit integer, thus
    truncating it to 2^32-1.  Therefore the comparison failed and sscanf()
    tried to parse the output starting at offset 2^32-1 which resulted in
    the crash.
    
    Introduced by commit:
        324d99a172848e4ff3fb7eb189f490bb4e6c53e5
        Record file system block size where known (#760709)
    
    Fix by following the same pattern of the other comparisons in
    ntfs::set_used_sectors() which checks if index is less than the output
    length.
    
    References:
    [1] std::string::find
        http://www.cplusplus.com/reference/string/string/find/
    [2] std::string::npos
        http://www.cplusplus.com/reference/string/string/npos/
    (Note that Glib::ustring is derived from std::string in the Standard C++
    library and provides a compatible interface).
    
    Bug 764658 - GParted crashes when reading NTFS usage when there is no
                 /dev/PTN entry

 src/ntfs.cc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/ntfs.cc b/src/ntfs.cc
index 0d46d24..50716be 100644
--- a/src/ntfs.cc
+++ b/src/ntfs.cc
@@ -143,7 +143,7 @@ void ntfs::set_used_sectors( Partition & partition )
                        N = T ;
 
                index = output.find( "Cluster size" );
-               if ( index == output.npos ||
+               if ( index >= output.length() ||
                     sscanf( output.substr( index ).c_str(), "Cluster size       : %Ld", &S ) != 1 )
                        S = -1;