Re: [FFmpeg-devel] [PATCH] mfenc: Use dlopen instead of LoadLibrary for loading mfplat.dll

[Timo Rothenpieler <timo@rothenpieler.org>]

On 25/05/2022 23:35, Martin Storsjö wrote:
> The dlopen wrapper contains code to make loading libraries safer,
> to avoid loading a potentially malicious DLL with the same name.
> 
> Signed-off-by: Martin Storsjö <martin@martin.st>
> ---
>   libavcodec/mfenc.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/mfenc.c b/libavcodec/mfenc.c
> index 17d0ec60bd..ab0b6b4145 100644
> --- a/libavcodec/mfenc.c
> +++ b/libavcodec/mfenc.c
> @@ -29,6 +29,7 @@
>   #include "libavutil/time.h"
>   #include "codec_internal.h"
>   #include "internal.h"
> +#include "compat/w32dlfcn.h"
>   
>   typedef struct MFContext {
>       AVClass *av_class;
> @@ -1158,7 +1159,7 @@ static int mf_load_library(AVCodecContext *avctx)
>       MFContext *c = avctx->priv_data;
>   
>   #if !HAVE_UWP
> -    c->library = LoadLibraryA("mfplat.dll");
> +    c->library = dlopen("mfplat.dll", 0);
>   
>       if (!c->library) {
>           av_log(c, AV_LOG_ERROR, "DLL mfplat.dll failed to open\n");
> @@ -1191,7 +1192,7 @@ static int mf_close(AVCodecContext *avctx)
>       if (c->library)
>           ff_free_mf(&c->functions, &c->mft);
>   
> -    FreeLibrary(c->library);
> +    dlclose(c->library);
>       c->library = NULL;
>   #else
>       ff_free_mf(&c->functions, &c->mft);

Very much a nit, given this code only ever runs on Windows, and dlsym is 
just a literal define to GetProcAddress, but mixing 
dlopen()+GetProcddress() like that looks kinda weird :D
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