Write error : dbclient

Matt Johnston matt at ucc.asn.au
Wed Sep 24 22:32:14 WST 2014

Hi Pratik,

I'm assuming that it is the session timeout that's causing
the disconnection.  The log on the OpenSSH server should
confirm that.

I think the only real solution would be to improve the speed
of libtommath on that device. Running a profiler to
determine the slowest parts would be the first step. I don't
know much about the device itself though it seems libtommath
performs quite badly - OpenSSL is generally faster. Looking
at the difference in its maths operations might help. It's
non-trivial work though.


On Wed, Sep 24, 2014 at 02:12:41PM +0530, pratik singh wrote:
> Hi,
> I am using Dropbear 0.48 with uClinux-dist. Currently dropbear server is
> working fine but while trying to run dbclient it throws write error. Some
> of the traces are:
> TRACE: leave process_packet
> TRACE: enter cli_sessionloop
> TRACE: enter send_msg_service_request: servicename='ssh-userauth'
> TRACE: enter encrypt_packet()
> TRACE: encrypt_packet type is 5
> TRACE: enter writemac
> TRACE: leave writemac
> TRACE: enter enqueue
> TRACE: leave enqueue
> TRACE: leave encrypt_packet()
> TRACE: leave send_msg_service_request
> TRACE: leave cli_sessionloop: sent userauth service req
> TRACE: enter write_packet
> TRACE: enter cli_tty_cleanup
> TRACE: leave cli_tty_cleanup: not in raw mode
> TRACE: enter session_cleanup
> TRACE: enter chancleanup
> TRACE: leave chancleanup
> TRACE: leave session_cleanup
> dbclient: connection to pratik at exited: error writing
> --------------------------------------------------------------------------------------------------------------
> I have tried the following:
> 1) Run dbclient with -K option but still getting the same write error
> 2) Run dbclient with -y option but still getting the same write error
> On further debugging I have found that this write comes because server (in
> this case Openssh) is getting timeout.
> I am running microblaze processor at about 60mhz with hardware
> multiplier, divider enabled.
> From the wireshark capture i have seen that server is sending "FIN"
> packet. also server is sending the 2 ssh packets in one reply packet.
> Do not know the reason of this behavior.
> I am facing this problem for connection between dbclient <----> Openssh.
> Please help as m stuck to this problem since very long. Appreciate your reply.
> Attached the pcap file for your reference. apply "ip.addr=="
> filter in pcap file. IP address is client having dbclient and other is
> server having openssh.
> -- 
> Thanks & Regards
> Pratik Singh

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