[FFmpeg-devel] [PATCH v2] libavformat/vapoursynth: Update to API version 4, load library at runtime

[Hendrik Leppkes]

On Mon, Jul 22, 2024 at 12:08 AM Stefan Oltmanns via ffmpeg-devel
<ffmpeg-devel at ffmpeg.org> wrote:
>
> Am 18.07.24 um 17:23 schrieb epirat07 at gmail.com:
> >
> >>>
> >>> Well, the DLL directory is added to PATH by the VapourSynth installer,
> >>> but for safety reasons ffmpeg explictly tells the LoadLibrary function
> >>> to only search the application directory and system32, quote from
> >>> w32dlfcn.h:
> >>>
> >>>> /**
> >>>>   * Safe function used to open dynamic libs. This attempts to improve program security
> >>>>   * by removing the current directory from the dll search path. Only dll's found in the
> >>>>   * executable or system directory are allowed to be loaded.
> >>>>   * @param name  The dynamic lib name.
> >>>>   * @return A handle to the opened lib.
> >>>>   */
> >>> So ffmpeg prevents that solution on purpose. Or should that behavior be
> >>> changed in the w32dlfcn.h?
> >>
> >> Oh, bummer. I would expect that overriding the PATH environment
> >> variable would work kind of like how LD_LIBRARY_PATH works on Linux. I
> >> don't know why that was changed. I don't really follow what goes on in
> >> Windowsland anymore. Does anyone else care to comment on this? Martin,
> >> maybe?
> >
> > IIRC this is done to prevent DLL injection attacks
> >
> > https://learn.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-security
> >
>
> So what's your proposal how to continue?
>
> I see different options with pros&cons:
>
>
> 1.
> Read the DLL path from registry, function for that could be located
> outside the VapourSynth module.
>
> Pro: Safest method to protect from DLL-injection
> Con: A lot of custom code/functionality for Windows
>

Relaxing security considerations to avoid a 10 line function seems not
worth it to me. So go with actually finding the correct path.

- Hendrik