[openssl-dev] Questions about ASYNC API for engines and moving read buffer.

[Matt Caswell]

On 02/06/17 11:00, Emeric Brun wrote:
> Hi,
> 
> I'm working on an ASYNC engine designed to offload crypto on multiple thread for monoproc applications.
> 
> No issue on asymetric crypto part but i'm facing a problem concerning ciphers:
> 
> When an SSL_read operation perform a do_cipher decrypt:
> 
> My engine defer the do_cipher to be processed by an other thread using the output buffer provided by to the do_cipher method.
> 
> After that it performs an ASYNC_pause_job(). On the application side it results on a WANT_ASYNC error.
> 
> The application consider that nothing was written on its output, and the buffer read buffer is reused for something else.
> 
> SSL_read is called a second time after receiving the event on the async fd. But this time the app used a different buffer.
> 
> On the engine side, i don't see any change on the do_cipher output buffer which would allow to manage the issue with a memcopy.
> 
> So my question is:
> 
> Is there a way to perform ciphering with an ASYNC engine when the app don't reuse the same buffer.

No, the async operation is running in it own fibre which is initialised
on first call, so it is still using the arguments from that initial
call. Subsequent calls won't "see" any changes in those args. We should
probably be more explicit about that in the docs.

Matt