Re: SSH Global Request

[Michal Vaško <mvasko@xxxxxxxxx>]

Hi Jakub,
I believe the comment is quite clear, the intention was to return SSH_OK even when the request is denied because it should be denied. It works just fine for blocking sockets and the resulting code is nicer. I think the author simply forgot about non-blocking sockets and that ssh_global_request() can return SSH_AGAIN, that is all.

Regards,
Michal

On Monday, March 9, 2020 09:40 CET, Jakub Jelen <jjelen@xxxxxxxxxx> wrote:

> On Mon, 2020-03-09 at 08:02 +0100, Michal Vaško wrote:
> > Hi Jakub,
> > thanks for the response. I was aware of the bug report but there was
> > some information that I have missed. Hopefully understanding it
> > better now I have one last request. I believe ssh_global_request()
> > with reply set to 1 should block until a response is received, which
> > is fine. But in case a non-blocking socket is used, it returns
> > immediately. Could the function ssh_send_keepalive() simply return
> > the value of ssh_global_request() instead of ignoring it? That way it
> > could be checked for SSH_AGAIN. I am fine with returning SSH_OK
> > irrespective of whether the client accepts or denies the request.
>
> Hello,
> it used to be this way, before the following commit:
>
> https://gitlab.com/libssh/libssh-mirror/commit/59ada799
>
> I am not completely clear about the reasoning for "dropping" the return
> value so better ask the author directly (in CC).
>
> Regards,
> Jakub
>
> > Regards,
> > Michal
> >
> > On Friday, March 6, 2020 16:54 CET, Jakub Jelen <jjelen@xxxxxxxxxx>
> > wrote:
> >
> > > On Fri, 2020-03-06 at 12:01 +0100, Michal Vaško wrote:
> > > > Hi Jakub,
> > > > right, I have not noticed the function before, thanks. However, I
> > > > am
> > > > not sure the API is suitable. What is the general behavior,
> > > > meaning
> > > > what happens if a reply is not sent back?
> > >
> > > Hi,
> > > see the discussion in, where we tried to understand this
> > > functionality
> > > in libssh (I did not implement that so I am not much better suited
> > > to
> > > hint here):
> > >
> > > https://bugs.libssh.org/T212
> > >
> > > > Is the connection automatically disconnected?
> > >
> > > The above function handles only the sending of the request. The
> > > answer
> > > is IGNORE message, which is handled with other packets. AFAIK if
> > > the
> > > TCP socket gets disconnected, your application can check using
> > > ssh_is_connected().
> > >
> > > > Is it possible to use custom max probes (how many keep-alive
> > > > packets
> > > > are sent unsuccessfully before a connection is considered dead)
> > > > and
> > > > probe interval (the interval between keep-alive packets) or some
> > > > specific values are always used?
> > >
> > > This is up to the application. The above API does just what it says
> > > in
> > > the name -- sends the keepalive packet to avoid disconnecting on
> > > TCP
> > > level. If you want to count how many times it was send and when.
> > > There
> > > is no simple way for libssh to handle this magically in background.
> > >
> > > > There is no documentation, that is why I am asking. Thanks for
> > > > providing these details.
> > >
> > > The server API is generally poorly documented so if you will learn
> > > more
> > > how does it work in real environment, contributions are welcomed.
> > >
> > > Regards,
> > > Jakub
> > >
> > > > Regards,
> > > > Michal
> > > >
> > > > On Friday, March 6, 2020 11:29 CET, Jakub Jelen <
> > > > jjelen@xxxxxxxxxx>
> > > > wrote:
> > > >
> > > > > On Fri, 2020-03-06 at 09:11 +0100, Michal Vaško wrote:
> > > > > > Hello,
> > > > > > I was wondering if the authors of libssh would have anything
> > > > > > against
> > > > > > making ssh_global_request() function from channels.h public.
> > > > > > It
> > > > > > would
> > > > > > enable implementing NETCONF Call Home SSH keep-alive [1].
> > > > > > Thanks.
> > > > >
> > > > > Hello,
> > > > > in server side, there is already API for sending keepalive
> > > > > messages:
> > > > > https://gitlab.com/libssh/libssh-mirror/-/blob/master/include/libssh/server.h#L368
> > > > >
> > > > > In the connection, only one of the peers needs to send the
> > > > > keepalive
> > > > > messages to keep a connection alive.
> > > > >
> > > > > If you need the similar functionality in the client, I would
> > > > > rather
> > > > > see
> > > > > it implemented by creating a new API function than exposing
> > > > > this
> > > > > internal function.
> > > > >
> > > > > Regards,
> > > > > --
> > > > > Jakub Jelen
> > > > > Senior Software Engineer
> > > > > Security Technologies
> > > > > Red Hat, Inc.
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > >
> > > --
> > > Jakub Jelen
> > > Senior Software Engineer
> > > Security Technologies
> > > Red Hat, Inc.
> > >
> > >
> >
> >
> >
> >
> --
> Jakub Jelen
> Senior Software Engineer
> Security Technologies
> Red Hat, Inc.
>
>