I need to install a webpage that allows visitors to upload a file via HTTP.
A very simple form and a very simple back-end CGI program.

The CGI program:
Must have source code.
Must run under Linux.
Must be C/C++ (not Perl or other scripting language).
Must be a very small, simple, single-purpose program (not a large,
comprehensive CGI form handler program).  Source code must be as
simple as possible, easily security-audited for buffer overflows, etc.

Files are uploaded to a single hardcoded directory.
No arbitrary size limit on the file size (could be 100MB).
The application is intended for low-volume, very occasional use by invitation.