[gparted] Prevent core dump with non-existent or invalid command line named device (#756434)

[Curtis Gedak <gedakc src gnome org>]

commit 663807802ff01f51633204f98c7f4410e9d0b9c7
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Mon Oct 12 14:33:14 2015 +0100

    Prevent core dump with non-existent or invalid command line named device (#756434)
    
    Naming a non-existent or invalid disk device on the command line causes
    GParted to dump core.  Non-existent device looks like this:
    
        # ./gpartedbin /dev/does-not-exist
        ======================
        libparted : 2.4
        ======================
        Could not stat device /dev/does-not-exist - No such file or directory.
        Could not stat device /dev/does-not-exist - No such file or directory.
        Backtrace has 10 calls on stack:
          10: /lib64/libparted.so.0(ped_assert+0x31) [0x7fcfd10b3e61]
          9: /lib64/libparted.so.0(+0x3fdfc12a0c) [0x7fcfd10b4a0c]
          8: /home/mike/bin/gpartedbin-0.23.0-master-63-g23b5ba4() [0x455028]
          7: /home/mike/bin/gpartedbin-0.23.0-master-63-g23b5ba4() [0x455090]
          6: /home/mike/bin/gpartedbin-0.23.0-master-63-g23b5ba4() [0x4550d5]
          5: /home/mike/bin/gpartedbin-0.23.0-master-63-g23b5ba4() [0x46723f]
          4: /usr/lib64/libglibmm-2.4.so.1() [0x3ff5834a8d]
          3: /lib64/libglib-2.0.so.0() [0x3fe086a374]
          2: /lib64/libpthread.so.0() [0x3fdf407a51]
          1: /lib64/libc.so.6(clone+0x6d) [0x3fdf0e893d]
        Assertion (dev != NULL) at device.c:227 in function ped_device_open() failed.
        Aborted (core dumped)
    
    And with an invalid device the output looks like this:
    
        # ./gpartedbin /dev/zero
        ======================
        libparted : 2.4
        ======================
        The device /dev/zero is so small that it cannot possibly store a file system or partition table.  
Perhaps you selected the wrong device?
        Error fsyncing/closing /dev/zero: Invalid argument
        The device /dev/zero is so small that it cannot possibly store a file system or partition table.  
Perhaps you selected the wrong device?
        Error fsyncing/closing /dev/zero: Invalid argument
        Backtrace has 10 calls on stack:
        ...
        [Same as above]
    
    Bisected the cause to this commit from 2015-03-09 in GParted 0.22.0.  It
    claimed to make no functional change.  That turned out not to be true.
        51ac4d56489653854cd22787238a14bfa66a6ad4
        Split get_device_and_disk() into two (#743181)
    
    Fix by simply adding the missed if condition in get_device().
    
    Bug 756434 - GParted dumps core when passing non-existent or invalid
                 device on the command line

 src/GParted_Core.cc |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/GParted_Core.cc b/src/GParted_Core.cc
index 5f51875..780aa18 100644
--- a/src/GParted_Core.cc
+++ b/src/GParted_Core.cc
@@ -3930,6 +3930,7 @@ bool GParted_Core::flush_device( PedDevice * lp_device )
 bool GParted_Core::get_device( const Glib::ustring & device_path, PedDevice *& lp_device, bool flush )
 {
        lp_device = ped_device_get( device_path.c_str() );
+       if ( lp_device )
        {
                if ( flush )
                        // Force cache coherency before going on to read the partition