#346 Bug Xcopy.exe can Fail when Destination Drive has 4+gb Free

[Craig W]

xcopy.exe (v1.4a and earlier) can fail when the destination drive has more than 4gb free space.

Source file xcopy.c @ line 756 calculates free disk space with -

  free_diskspace = (unsigned long) disktable.df_avail * disktable.df_sclus * disktable.df_bsec;

The free_diskspace unsigned long and cast overflows and wraps when it hits a 4 gigabyte boundary, e.g 4.1gb gets reported as 0.1gb. Will produce random "insufficient free space" errors even when a drive actually has enough free space.

There's several other code files that have the same flaw, probably worth auditing the code base for getdfree()/_dos_getdiskfree().

Cheers

[fritz.mueller]

This bug is still active on 2024-08-05! I just tried to copy bigger files (1,5 GB, should be no problem) on a 150 GB virtual HD where 141,541 MBytes are free!
The first 10 of 16 files were done.

There seems to be an uncompiled version 1.5 at: https://github.com/FDOS/xcopy

[fritz.mueller]

Thank you very much! Seems to be fixed now!
From my side the thread can be closed!

[fritz.mueller]

just an additional comment:

I added two different Linux iso files on an actual virtual FD machine
which a drive letter that has full 2TB FAT32 capacity (Bernds kernel) -
and ran xcopy to copy all files (ca. 3,9 GB and ca. 2 GB) on to this HD.
It worked fine. I noticed not problems, no crash, nothing.

So I think it was a good idea to close the bug.

Fritz

Am 2025-08-12 02:02, schrieb Jim Hall:

• status: open --> closed-fixed
• Comment:

Marking as closed-fixed since XCOPY was updated in a later release to fix stack and disk space issues, as Fritz mentioned.

[bugs:#346] [1] Bug Xcopy.exe can Fail when Destination Drive has 4+gb Free

Status: closed-fixed
Group: freedos13
Labels: xcopy _dos_getdiskfree
Created: Thu Aug 12, 2021 11:03 AM UTC by Craig W
Last Updated: Mon Aug 12, 2024 12:29 PM UTC
Owner: nobody

xcopy.exe (v1.4a and earlier) can fail when the destination drive has more than 4gb free space.

Source file xcopy.c @ line 756 calculates free disk space with -

free_diskspace = (unsigned long) disktable.df_avail * disktable.df_sclus * disktable.df_bsec;

The free_diskspace unsigned long and cast overflows and wraps when it hits a 4 gigabyte boundary, e.g 4.1gb gets reported as 0.1gb. Will produce random "insufficient free space" errors even when a drive actually has enough free space.

There's several other code files that have the same flaw, probably worth auditing the code base for getdfree()/_dos_getdiskfree().

Cheers

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[Jim Hall]

Marking as closed-fixed since XCOPY was updated in a later release to fix stack and disk space issues, as Fritz mentioned.