; 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 <http://www.gnu.org/licenses/>.
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