Subversion Repositories Kolibri OS

;    ssh_transport.inc - SSH transport layer

;

;    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 .

struct  ssh_packet_header

        packet_length   dd ?    ; The length of the packet in bytes, not including 'mac' or the

                                ; 'packet_length' field itself.

        padding_length  db ?    ; Length of 'random padding' (bytes).

        message_code    db ?    ; First byte of payload

ends

proc padding_zero

        xor     eax, eax

        ret

endp

proc ssh_recv_packet connection, flags

locals

        data_length     dd ?    ; Total length of packet without MAC

        socket_error    dd ?

endl

        DEBUGF  2, "> "

; Receive first block (Read length, padding length, message code)

        mov     ebx, [connection]

        mov     ecx, [ebx+ssh_connection.socketnum]

        mov     esi, [ebx+ssh_connection.rx_crypt_blocksize]

        lea     edx, [ebx+ssh_connection.rx_buffer]

        mov     edi, [flags]

        mcall   recv

        mov     [socket_error], ebx

        DEBUGF  1, "chunk = %u ", eax

        mov     ebx, [connection]

        cmp     eax, [ebx+ssh_connection.rx_crypt_blocksize]

        jne     .fail

; Decrypt first block

        cmp     [ebx+ssh_connection.rx_crypt_proc], 0

        je      @f

        pusha

        lea     esi, [ebx+ssh_connection.rx_buffer]

        stdcall [ebx+ssh_connection.rx_crypt_proc], [ebx+ssh_connection.rx_crypt_ctx_ptr], esi, esi

        popa

  @@:

; Check data length

        mov     esi, [ebx+ssh_connection.rx_buffer.packet_length]

        bswap   esi                                             ; convert length to little endian

        mov     [ebx+ssh_connection.rx_buffer.packet_length], esi

        DEBUGF  1, "packet length=%u ", esi

        cmp     esi, BUFFERSIZE

        ja      .fail                                           ; packet is too large

; Calculate amount of remaining data

        add     esi, 4                                          ; Packet length field itself is not included in the count

        sub     esi, [ebx+ssh_connection.rx_crypt_blocksize]    ; Already received this amount of data

        add     esi, [ebx+ssh_connection.rx_mac_length]

        jz      .got_all_data

; Receive remaining data

        lea     edx, [ebx+ssh_connection.rx_buffer]

        add     edx, [ebx+ssh_connection.rx_crypt_blocksize]

        mov     ecx, [ebx+ssh_connection.socketnum]

        mov     edi, [flags]

  .receive_loop:

        mcall   recv

        DEBUGF  1, "chunk = %u ", eax

        cmp     eax, 0

        jbe     .fail

        add     edx, eax

        sub     esi, eax

        jnz     .receive_loop

; Decrypt data

        mov     ebx, [connection]

        cmp     [ebx+ssh_connection.rx_crypt_proc], 0

        je      .decrypt_complete

        mov     ecx, [ebx+ssh_connection.rx_buffer.packet_length]

        add     ecx, 4                                          ; Packet_length field itself

        sub     ecx, [ebx+ssh_connection.rx_crypt_blocksize]    ; Already decrypted this amount of data

        jz      .decrypt_complete

        lea     esi, [ebx+ssh_connection.rx_buffer]

        add     esi, [ebx+ssh_connection.rx_crypt_blocksize]

  .decrypt_loop:

        pusha

        stdcall [ebx+ssh_connection.rx_crypt_proc], [ebx+ssh_connection.rx_crypt_ctx_ptr], esi, esi

        popa

        add     esi, [ebx+ssh_connection.rx_crypt_blocksize]

        sub     ecx, [ebx+ssh_connection.rx_crypt_blocksize]

        jnz     .decrypt_loop

  .decrypt_complete:

; Authenticate message

        cmp     [ebx+ssh_connection.rx_mac_proc], 0

        je      .mac_complete

        lea     esi, [ebx+ssh_connection.rx_seq]

        mov     ecx, [ebx+ssh_connection.rx_buffer.packet_length]

        add     ecx, 8                                          ; packet_length field itself + sequence number

        lea     eax, [ebx+ssh_connection.rx_mac_ctx]

        mov     edx, [ebx+ssh_connection.rx_buffer.packet_length]

        bswap   edx                                             ; convert length to big endian

        mov     [ebx+ssh_connection.rx_buffer.packet_length], edx

        stdcall [ebx+ssh_connection.rx_mac_proc], eax, esi, ecx

        mov     edx, [ebx+ssh_connection.rx_buffer.packet_length]

        bswap   edx                                             ; convert length to little endian

        mov     [ebx+ssh_connection.rx_buffer.packet_length], edx

        lea     esi, [ebx+ssh_connection.rx_mac_ctx]

        lea     edi, [ebx+ssh_connection.rx_buffer]

        add     edi, [ebx+ssh_connection.rx_buffer.packet_length]

        add     edi, 4

        mov     ecx, [ebx+ssh_connection.rx_mac_length]

        shr     ecx, 2

        repe cmpsd

        jne     .mac_failed

  .mac_complete:

        add     byte[ebx+ssh_connection.rx_seq+3], 1            ; Update sequence counter

        adc     byte[ebx+ssh_connection.rx_seq+2], 0

        adc     byte[ebx+ssh_connection.rx_seq+1], 0

        adc     byte[ebx+ssh_connection.rx_seq+0], 0

; Return useful data length to the caller via eax register

  .got_all_data:

        mov     eax, [ebx+ssh_connection.rx_buffer.packet_length]

        movzx   ebx, [ebx+ssh_connection.rx_buffer.padding_length]

        sub     eax, ebx

        DEBUGF  1, "useful data length=%u\n", eax

        ret

  .fail:

        DEBUGF  3, "ssh_recv_packet failed!\n"

        mov     eax, -1

        mov     ebx, [socket_error]

        ret

  .mac_failed:

        DEBUGF  3, "ssh_recv_packet MAC failed!\n"

        mov     eax, -2

        mov     ebx, [socket_error]

        ret

endp

proc ssh_send_packet connection, buf, payload_size, flags

locals

        packet_size    dd ?

endl

        DEBUGF  2, "< "

; Check how many bytes we should pad

        mov     eax, [payload_size]

        inc     eax                     ; padding length byte

        lea     edx, [eax+4]            ; total packet size (without padding and MAC)

        mov     [packet_size], edx

        mov     ecx, [connection]

        mov     ebx, [ecx+ssh_connection.tx_pad_size]

        dec     ebx

        and     edx, ebx

        neg     edx

        add     edx, [ecx+ssh_connection.tx_pad_size]

        add     edx, [ecx+ssh_connection.tx_pad_size]

        DEBUGF  1, "padding %u bytes ", edx

        add     [packet_size], edx      ; total packet size with padding

; Start building the packet

; First comes the packet length, in network byte order ofcourse.

        add     eax, edx

        DEBUGF  1, "total size: %u ", eax

        bswap   eax

        lea     edi, [ecx+ssh_connection.tx_buffer]

        stosd

; Then the padding length

        mov     al, dl

        stosb

; And the actual payload bytes

        mov     esi, [buf]

        mov     ecx, [payload_size]

        rep movsb

; Append the packet with #edx padding bytes.

; Since we must pad at least 8 bytes, we can always use DWORD writes.

; First do an (unaligned) write exactly following the data

        dec     edx

        mov     esi, edx

        shr     esi, 2          ; number dwords

        mov     ebx, edx

        and     ebx, 3

        inc     ebx             ; number bytes in first write (1-4)

        mov     edx, [connection]

        call    [edx+ssh_connection.tx_pad_proc]

        mov     dword[edi], eax

        add     edi, ebx

; Then, do as many aligned writes as nescessary

        mov     ebx, [connection]

  @@:

        call    [ebx+ssh_connection.tx_pad_proc]

        stosd

        dec     esi

        jnz     @r

; Append the packet with Message Authentication Code

        mov     edx, [connection]

        cmp     [edx+ssh_connection.tx_mac_proc], 0

        je      .mac_complete

        DEBUGF  1, "MAC sequence number: 0x%x\n", [edx+ssh_connection.tx_seq]

        lea     esi, [edx+ssh_connection.tx_seq]

        mov     ecx, [packet_size]

        add     ecx, 4                                          ; Sequence number length

        lea     eax, [edx+ssh_connection.tx_mac_ctx]

        stdcall [edx+ssh_connection.tx_mac_proc], eax, esi, ecx

        lea     esi, [edx+ssh_connection.tx_mac_ctx]

        lea     edi, [edx+ssh_connection.tx_buffer]

        add     edi, [packet_size]

        mov     ecx, [edx+ssh_connection.tx_mac_length]

        shr     ecx, 2

        rep movsd

  .mac_complete:

        add     byte[edx+ssh_connection.tx_seq+3], 1            ; Update sequence counter

        adc     byte[edx+ssh_connection.tx_seq+2], 0

        adc     byte[edx+ssh_connection.tx_seq+1], 0

        adc     byte[edx+ssh_connection.tx_seq+0], 0

; Now, encrypt everything but MAC

        cmp     [edx+ssh_connection.tx_crypt_proc], 0

        je      .encrypt_complete

        lea     esi, [edx+ssh_connection.tx_buffer]

        mov     ecx, [packet_size]

  .encrypt_loop:

        pusha

        stdcall [edx+ssh_connection.tx_crypt_proc], [edx+ssh_connection.tx_crypt_ctx_ptr], esi, esi

        popa

        add     esi, [edx+ssh_connection.tx_crypt_blocksize]

        sub     ecx, [edx+ssh_connection.tx_crypt_blocksize]

        jnz     .encrypt_loop

  .encrypt_complete:

; Send the packet

        mov     ebx, [connection]

        mov     ecx, [ebx+ssh_connection.socketnum]

        lea     edx, [ebx+ssh_connection.tx_buffer]

        mov     esi, [packet_size]

        add     esi, [ebx+ssh_connection.tx_mac_length]

        mov     edi, [flags]

        mcall   send

        DEBUGF  1, "\n"

        ret

endp