Re: Closure of socket by shutdown function

[Andreas Schneider <asn@xxxxxxxxxxxxxx>]

On Friday 30 May 2014 06:20:18 Aarthi wrote:
> Hi All,

Hi,

> We are facing an issue while using libssh 0.6.3 integrated with an
> application, say app A. app A runs as a process and libssh is linked to it.
> The app A disables SSH by closing the existing SSH sessions using
> ssh_disconnect(session) and doing ssh_free() and ssh_bind_free(). SSH is
> enabled by ssh_new () ,ssh_bind_listen(),and ssh_bind_accept().
> 
> 
> The application A forks some processes during its execution. The issue
> occurs when SSH is enabled a session is established, process app B is
> forked, SSH is disabled and enabled.
> 
> 1) Initially SSH is enbaled
> 2) Fork process B
> 3) Disable SSH
> 4) Enable SSH
> In the above process during step 2 the “app B” process inherits the ports
> created by “app A” process. In step 3 the port is closed by “app A” process
> but since the “app B” process is running the port 22 remains open (its kept
> in this way by the Operating System)). At step4 when port 22 is bound again
> it returns error as the port is kept open by the Operating System (app B
> process is still running).
> This is a standard system issue with forking of processes. This issue could
> occur when “application A” forks any process during SSH disable and that
> process lives for a while. To solve it the socket has to be “shutdown”
> before “closing”.
> 
> the following patch can be applied to bind.c to overcome the issue.
> 
> Libssh -> src/bind.c
> void ssh_bind_free(ssh_bind sshbind){
>   int i;
>   if (sshbind == NULL) {
>     return;
>   }
>  if (sshbind->bindfd >= 0) {
> #ifdef _WIN32
>     closesocket(sshbind->bindfd);
> #else
> +   shutdown(sshbind->bindfd,2);
>     close(sshbind->bindfd);
> #endif
>   }
>   sshbind->bindfd = SSH_INVALID_SOCKET;
> 
> Please let us know your thoughts on this patch, and the release where this
> patch could be integrated to the main line.

I don't think this is a common problem. It is a special case for how you 
implemented forking and handling of SSH.

So you should call

fd = ssh_bind_getfd(bind);
shutdown(fd, 2)
ssh_bind_free(bind);


Cheers,


	-- andreas


-- 
Andreas Schneider                   GPG-ID: CC014E3D
www.cryptomilk.org                asn@xxxxxxxxxxxxxx