libssh: Client having trouble reading data from the server

["Boyle, Aaron" <aaron.boyle@xxxxxxx>]

Hi,

We are using the latest version of libssh (0.9.0) to create a local ssh server in our codebase. However, we are having issues with the client, which uses libssh2 (1.9.0), reading data from the server. We run this issue on multiple distros, including Centos 6, Centos 7, Red Hat 6, Red Hat 7, Ubuntu 14.04, Ubuntu 16.04, Ubuntu 18.04, Debian 8, Debian 9, SUSE LE 12. But this issue arises primarily on Ubuntu 18.04, Debian 9 and SUSE LE 12. We also ported the libssh2 client to libssh aswell, but the same issue still arose.

We narrowed down the issue in the “packet.c” source file in the function “ssh_packet_register_socket_callback”. If we change

session->socket_callbacks.controlflow=ssh_packet_socket_controlflow_callback

to

session->socket_callbacks.controlflow = session->client ? ssh_packet_socket_controlflow_callback : NULL

to only call it on the client, it works fine for us. But we’re not certain if this workaround is viable. Can you provide any help?


Here is some extra debugging info from the ssh server on gdb:

(gdb) bt full
#0  0x0000000000000090 in ?? ()
No symbol table info available.
#1  0x0000555555588fbf in ssh_packet_socket_controlflow_callback (code=2, userdata=0x55555580c690)
    at /home/aaron/Domino/external/libssh/src/packet.c:1384
        i = 0x5555558185e0
        cb = 0x5555558150c0
        session = 0x55555580c690
        it = 0x555555814f70
        channel = 0x555555815440
        __func__ = "ssh_packet_socket_controlflow_callback"
#2  0x00005555555954a6 in ssh_socket_pollcallback (p=0x55555580dbf0, fd=4, revents=4,
    v_s=0x555555810290) at /home/aaron/Domino/external/libssh/src/socket.c:359
        len = 0
        s = 0x555555810290
        buffer = "\274\317\034\304]+l\304{\304\357W5>6\371\033\243\314\320'\235\363\372\064LVO\305\b\321\360\006\263\307\026\306\062\207\371\002\223\223\301\361+\261\263\230\037\376\063\032\064\372E\\f\366\237\020\230\302Iq\371\255\001\374B\265\023\017z\353\225\370\261Sd>J\325(H\032\b\305\021\346\233\311\356\066+\004\306Vܸ\375\003\364\250\361D\331_aV\033l`\314\377\377\377\177\000\000\020YO\366\377\177\000\000\001\200\255\373a2-n`\314\377\377\377\177\000\000`\314\377\377\377\177\000\000`\314\377\377\377\177\000\000`\314\377\377\377\177\000\000z\314\377\377\377\177\000\000\337\314\377\377\377\177\000\000`\314\377\377\377\177\000\000\337\314\070\070\067\065\066\066\000"...
        nread = 0
        rc = 0
        err = 0
        errlen = 4
        __func__ = "ssh_socket_pollcallback"
#3  0x00005555555927b1 in ssh_poll_ctx_dopoll (ctx=0x555555811660, timeout=1000)
    at /home/aaron/Domino/external/libssh/src/poll.c:702
        ret = 0
        rc = 1
        i = 0
        used = 2
        p = 0x55555580dbf0
        fd = 4
        revents = 4
        ts = {seconds = 11917, useconds = 198958}
#4  0x0000555555592c70 in ssh_event_dopoll (event=0x555555815030, timeout=1000)
    at /home/aaron/Domino/external/libssh/src/poll.c:963
        rc = 21845
#5  0x000055555556d156 in main ()
No symbol table info available.


(gdb) f 1
#1  0x0000555555588fbf in ssh_packet_socket_controlflow_callback (code=2, userdata=0x55555580c690)
    at /home/aaron/Domino/external/libssh/src/packet.c:1384
1384                   ssh_callbacks_execute_list(channel->callbacks,
(gdb) p *cb
$1 = {size = 136, userdata = 0x5555558185a0,
  channel_data_function = 0x55555556be11 <copy_channel_to_fd(ssh_session_struct*, ssh_channel_struct*, void*, unsigned int, int, void*)>, channel_eof_function = 0x0, channel_close_function = 0x30,
  channel_signal_function = 0x30, channel_exit_status_function = 0x555555814b70,
  channel_exit_signal_function = 0x2767ec47e2d143c3,
  channel_pty_request_function = 0xfa053776daf43a53,
  channel_shell_request_function = 0x924d5d1d963e81ff, channel_auth_agent_req_function = 0x60,
  channel_x11_req_function = 0x30, channel_pty_window_change_function = 0x555555812430,
  channel_exec_request_function = 0x5555555c2c19, channel_env_request_function = 0x0,
  channel_subsystem_request_function = 0x555555815150, channel_write_wontblock_function = 0x90}


Regards,
Aaron