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

[Stefan Oltmanns via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

Am 22.07.24 um 00:15 schrieb Hendrik Leppkes:
> On Mon, Jul 22, 2024 at 12:08 AM Stefan Oltmanns via ffmpeg-devel
> <ffmpeg-devel@ffmpeg.org> wrote:
>>
>> Am 18.07.24 um 17:23 schrieb epirat07@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.
>

Ok, should that function remain in the vapoursynth module, or should
handling the registry be done in a header like "compat/w32registry.h"?

An external file with a universal function would of course require more
code.


Best regards
Stefan

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