;    sshlib_connection.inc - SSH connection
;
;    Copyright (C) 2016-2021 Jeffrey Amelynck
;
;    This program is free software: you can redistribute it and/or modify
;    it under the terms of the GNU General Public License as published by
;    the Free Software Foundation, either version 3 of the License, or
;    (at your option) any later version.
;
;    This program is distributed in the hope that it will be useful,
;    but WITHOUT ANY WARRANTY; without even the implied warranty of
;    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;    GNU General Public License for more details.
;
;    You should have received a copy of the GNU General Public License
;    along with this program.  If not, see <http://www.gnu.org/licenses/>.

proc sshlib_connect con_ptr, hostname_sz

locals
        socketnum       dd ?
        sockaddr        sockaddr_in
        ctx_ptr         dd ?
endl

        mov     edi, [con_ptr]
        lea     eax, [edi + sshlib_connection.part_ex_hash_ctx]
        mov     [ctx_ptr], eax

; Set default values in sockaddr struct
        mov     [sockaddr.sin_family], AF_INET4
        mov     [sockaddr.sin_port], 22 shl 8

; Parse hostname_sz
; Verify length, extract port number if given and copy base url to sshlib_connection struct
; Port number, if provided, will be written in sockaddr struct.
; Hostname ends with any character equal to 0x20 or lower

        mov     esi, [hostname_sz]
        lea     edi, [edi + sshlib_connection.hostname_sz]
        mov     ecx, MAX_HOSTNAME_LENGTH
  @@:
        dec     ecx
        jz      .err_hostname
        lodsb
        cmp     al, ':'
        je      .do_port
        stosb
        cmp     al, 0x20
        ja      @r
        mov     byte[edi-1], 0
        jmp     .hostname_ok

  .do_port:
        xor     eax, eax
        xor     ebx, ebx
        mov     byte[edi-1], 0
  .portloop:
        lodsb
        cmp     al, 0x20
        jbe     .port_done
        sub     al, '0'
        jb      .err_hostname
        cmp     al, 9
        ja      .err_hostname
        lea     ebx, [ebx*4+ebx]
        shl     ebx, 1
        add     ebx, eax
        jmp     .portloop
  .port_done:
        xchg    bl, bh
        mov     [sockaddr.sin_port], bx

  .hostname_ok:
; resolve name
        push    esp     ; reserve stack place
        push    esp
        mov     eax, [con_ptr]
        lea     eax, [eax+sshlib_connection.hostname_sz]
        invoke  getaddrinfo, eax, 0, 0
        pop     esi
; test for error
        test    eax, eax
        jnz     .err_hostname

; convert IP address to decimal notation
        mov     eax, [esi+addrinfo.ai_addr]
        mov     eax, [eax+sockaddr_in.sin_addr]
        mov     [sockaddr.sin_addr], eax
        invoke  inet_ntoa, eax
; write result
        stdcall sshlib_callback_connecting, [con_ptr], eax
; free allocated memory
        invoke  freeaddrinfo, esi

; Create socket
        mcall   socket, AF_INET4, SOCK_STREAM, 0
        cmp     eax, -1
        jz      .err_sock
        mov     [socketnum], eax
        mov     ebx, [con_ptr]
        mov     [ebx + sshlib_connection.socketnum], eax

; Connect
        DEBUGF  2, "Connecting to server\n"
        lea     edx, [sockaddr]
        mcall   connect, [socketnum], , sizeof.sockaddr_in
        test    eax, eax
        jnz     .err_sock

; Start calculating hash
        invoke  sha2_256_init, [ctx_ptr]
; HASH: string  V_C, the client's version string (CR and NL excluded)
        invoke  sha2_256_update, [ctx_ptr], ssh_ident_ha, ssh_msg_ident.length+4-2

; >> Send our identification string
        DEBUGF  2, "Sending ID string\n"
        mcall   send, [socketnum], ssh_msg_ident, ssh_msg_ident.length, 0
        cmp     eax, -1
        je      .err_sock

; << Check protocol version of server
        mov     edx, [con_ptr]
        lea     edx, [edx + sshlib_connection.rx_buffer + 4]
        mcall   recv, [socketnum], , PACKETSIZE, 0
        cmp     eax, -1
        je      .err_sock

        DEBUGF  2, "Received ID string\n"
        cmp     dword[edx], "SSH-"
        jne     .err_proto
        cmp     dword[edx+4], "2.0-"
        jne     .err_proto

; HASH: string  V_S, the server's version string (CR and NL excluded)
        lea     ecx, [eax+2]
        sub     eax, 2
        bswap   eax
        sub     edx, 4
        mov     dword[edx], eax
        invoke  sha2_256_update, [ctx_ptr], edx, ecx

; >> Key Exchange init
        mov     eax, [con_ptr]
        mov     [eax + sshlib_connection.status], SSHLIB_CON_STAT_INIT

        mov     [eax + sshlib_connection.algo_kex], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_hostkey], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_crypt_rx], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_crypt_tx], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_mac_rx], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_mac_tx], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_compr_rx], SSHLIB_ALGO_NONE
        mov     [eax + sshlib_connection.algo_compr_tx], SSHLIB_ALGO_NONE

        mov     [eax + sshlib_connection.rx_mac_seqnr], 0
        mov     [eax + sshlib_connection.tx_mac_seqnr], 0
        mov     [eax + sshlib_connection.rx_crypt_blocksize], 4             ; minimum blocksize
        mov     [eax + sshlib_connection.tx_crypt_blocksize], 4
        mov     [eax + sshlib_connection.rx_crypt_proc], sshlib_crypt_null
        mov     [eax + sshlib_connection.tx_crypt_proc], sshlib_crypt_null
        mov     [eax + sshlib_connection.rx_mac_proc], 0
        mov     [eax + sshlib_connection.tx_mac_proc], 0
        mov     [eax + sshlib_connection.rx_mac_length], 0
        mov     [eax + sshlib_connection.tx_mac_length], 0
        mov     [eax + sshlib_connection.tx_pad_size], 8
        mov     [eax + sshlib_connection.tx_pad_proc], sshlib_padd_null

        DEBUGF  2, "Sending KEX init\n"
        mov     edi, ssh_msg_kex.cookie
        call    MBRandom
        stosd
        call    MBRandom
        stosd
        call    MBRandom
        stosd
        call    MBRandom
        stosd
        stdcall sshlib_send_packet, [con_ptr], ssh_msg_kex, ssh_msg_kex.length, 0
        cmp     eax, -1
        je      .err_sock

; HASH: string  I_C, the payload of the client's SSH_MSG_KEXINIT
        mov     esi, [con_ptr]
        mov     eax, [esi+sshlib_connection.tx_buffer.packet_length]
        bswap   eax
        movzx   ebx, [esi+sshlib_connection.tx_buffer.padding_length]
        sub     eax, ebx
        dec     eax
        lea     edx, [eax+4]
        bswap   eax
        lea     esi, [esi+sshlib_connection.tx_buffer+1]
        mov     dword[esi], eax
        invoke  sha2_256_update, [ctx_ptr], esi, edx

; << Check key exchange init of server
        stdcall sshlib_recv_packet, [con_ptr], 0
        cmp     eax, -1
        je      .err_sock

        mov     esi, [con_ptr]
        cmp     [esi + sshlib_connection.rx_buffer.message_code], SSH_MSG_KEXINIT
        jne     .err_proto
        DEBUGF  2, "Received KEX init\n"

        lea     esi, [esi + sshlib_connection.rx_buffer + sizeof.ssh_packet_header + 16]
        lodsd
        bswap   eax
        DEBUGF  1, "kex_algorithms: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "server_host_key_algorithms: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "encryption_algorithms_client_to_server: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "encryption_algorithms_server_to_client: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "mac_algorithms_client_to_server: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "mac_algorithms_server_to_client: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "compression_algorithms_client_to_server: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "compression_algorithms_server_to_client: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "languages_client_to_server: %s\n", esi
        add     esi, eax
        lodsd
        bswap   eax
        DEBUGF  1, "languages_server_to_client: %s\n", esi
        add     esi, eax
        lodsb
        DEBUGF  1, "KEX First Packet Follows: %u\n", al

; TODO: parse this structure and set algorithm codes accordingly
; FIXME: hardcoded for now
        mov     esi, [con_ptr]
        mov     [esi+sshlib_connection.algo_kex], SSHLIB_KEX_DH_SHA256
        mov     [esi+sshlib_connection.algo_hostkey], SSHLIB_HOSTKEY_RSA
        mov     [esi+sshlib_connection.algo_crypt_rx], SSHLIB_CRYPT_AES256_CTR
        mov     [esi+sshlib_connection.algo_crypt_tx], SSHLIB_CRYPT_AES256_CTR
        mov     [esi+sshlib_connection.algo_mac_rx], SSHLIB_HMAC_SHA2_256
        mov     [esi+sshlib_connection.algo_mac_tx], SSHLIB_HMAC_SHA2_256
        mov     [esi+sshlib_connection.algo_compr_rx], SSHLIB_COMPR_NONE
        mov     [esi+sshlib_connection.algo_compr_tx], SSHLIB_COMPR_NONE

; HASH: string I_S, the payload of the servers's SSH_MSG_KEXINIT
        mov     esi, [con_ptr]
        mov     eax, [esi+sshlib_connection.rx_buffer.packet_length]
        movzx   ebx, [esi+sshlib_connection.rx_buffer.padding_length]
        sub     eax, ebx
        dec     eax
        lea     edx, [eax+4]
        bswap   eax
        lea     esi, [esi+sshlib_connection.rx_buffer+1]
        mov     dword[esi], eax
        invoke  sha2_256_update, [ctx_ptr], esi, edx

; Exchange keys with the server

        stdcall sshlib_dh_gex, [con_ptr]
        test    eax, eax
        jnz     .err

; Re-seed RNG for padding bytes

        call    create_seed
        call    init_random

        xor     eax, eax
        ret

  .err_hostname:
        mov     eax, SSHLIB_ERR_HOSTNAME
        ret

  .err_sock:
        mov     eax, SSHLIB_ERR_SOCKET
        ret

  .err_proto:
        mov     eax, SSHLIB_ERR_PROTOCOL
        ret

  .err:
        ret

endp




; Handle common messages and return to caller for specific ones
proc sshlib_msg_handler, con_ptr, flags

  .recv:
; Send a window update if advertised window drops below half
        cmp     [ssh_chan.rcv_wnd], BUFFERSIZE/2
        ja      .no_wnd
        mov     eax, BUFFERSIZE
        bswap   eax
        mov     [ssh_msg_channel_window_adjust.wnd], eax
        stdcall sshlib_send_packet, [con_ptr], ssh_msg_channel_window_adjust, ssh_msg_channel_window_adjust.length, 0
        mov     [ssh_chan.rcv_wnd], BUFFERSIZE
  .no_wnd:

; Receive 1 SSH packet
        stdcall sshlib_recv_packet, [con_ptr], [flags]
        cmp     eax, 0
        jle     .ret

        mov     esi, [con_ptr]
        lea     esi, [esi + sshlib_connection.rx_buffer]
        mov     al, [esi + ssh_packet_header.message_code]
        inc     esi

        cmp     al, SSH_MSG_DISCONNECT
        je      .disc
        cmp     al, SSH_MSG_IGNORE
        je      .ign
        cmp     al, SSH_MSG_DEBUG
        je      .dbg
        cmp     al, SSH_MSG_GLOBAL_REQUEST
        je      .glob_req
        cmp     al, SSH_MSG_CHANNEL_WINDOW_ADJUST
        je      .chan_win_adj
;        cmp     al, SSH_MSG_CHANNEL_REQUEST
;        je      .chan_req
        cmp     al, SSH_MSG_CHANNEL_EOF
        je      .chan_eof
        cmp     al, SSH_MSG_CHANNEL_CLOSE
        je      .chan_close

  .ret:
        ret

  .disc:
        DEBUGF  3, "SSH: Disconnect message received\n"
        mov     eax, SSHLIB_ERR_DISCONNECTING
        ret

  .ign:
        DEBUGF  3, "SSH: Ignore MSG received\n"
        jmp     .recv

  .dbg:
        DEBUGF  3, "SSH: Debug MSG received\n"
        ;TODO
        jmp     .recv

  .glob_req:
        DEBUGF  3, "SSH: Global MSG received\n"
        ;TODO
        jmp     .recv

  .chan_win_adj:
        mov     eax, dword[esi]
        bswap   eax
        mov     [ssh_chan.snd_wnd], eax
        ; TODO: validate channel number, act accordingly
        DEBUGF  3, "SSH: Channel %u window update received\n", eax
        jmp     .recv

  .chan_eof:
        mov     eax, dword[esi]
        bswap   eax
        ; TODO: validate channel number, act accordingly
        DEBUGF  3, "SSH: Channel %u EOF received\n", eax
        jmp     .recv

  .chan_close:
        mov     eax, dword[esi]
        bswap   eax
        ; TODO: validate channel number
        DEBUGF  3, "SSH: Channel %u close received\n", eax
        ; Reply with close message
        stdcall sshlib_send_packet, [con_ptr], ssh_msg_channel_close, ssh_msg_channel_close.length, 0
        xor     eax, eax
        ret

endp