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Add IP and UDP header to OFFER attempt

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It d oesn't quite work, but it looks convincing.  UDP checksum may
need to be added, and beyond that explore changes to the payload since
it is likely not enough DHCP was provided.
This commit is contained in:
Jarrod Johnson 2020-03-19 18:39:32 -04:00
parent b7d85b2166
commit fcd73399fa
1 changed files with 26 additions and 2 deletions
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28
confluent_server/confluent/discovery/protocols/pxe.py
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@ -32,6 +32,19 @@ import struct
libc = ctypes.CDLL(ctypes.util.find_library('c'))
iphdr = b'\x45\x00\x00\x00\x00\x00\x00\x00\x40\x11\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff'
constiphdrsum = b'\x85\x11'
udphdr = b'\x00\x43\x00\x44\x00\x00\x00\x00'
def _ipsum(data):
currsum = 0
for datum in struct.unpack('!' + 'H' * (len(data) // 2), data):
currsum += datum
if currsum >> 16:
currsum &= 0xffff
currsum += 1
return currsum
class sockaddr_ll(ctypes.Structure):
_fields_ = [('sll_family', ctypes.c_ushort),
('sll_protocol', ctypes.c_ushort),
@ -337,6 +350,10 @@ def check_reply(node, info, packet, sock, cfg, reqview):
return
reply = bytearray(1024)
repview = memoryview(reply)
repview[:20] = iphdr
repview[12:16] = myipn
repview[20:28] = udphdr
repview = repview[28:]
repview[0] = 2
repview[1:10] = reqview[1:10] # duplicate txid, hwlen, and others
repview[10] = 0x80 # always set broadcast
@ -355,6 +372,12 @@ def check_reply(node, info, packet, sock, cfg, reqview):
repview[245:249] = myipn
repview[249:255] = b'\x33\x04\x00\x00\x00\xf0'
repview[255] = 0xff # end of options, should always be last byte
repview = memoryview(reply)
pktlen = struct.pack('!H', 256 + 28) # ip+udp = 28
repview[2:4] = pktlen
curripsum = ~(_ipsum(constiphdrsum + pktlen + myipn)) & 0xffff
repview[10:12] = struct.pack('!H', curripsum)
repview[24:26] = struct.pack('!H', 256 + 8)
tsock = socket.socket(socket.AF_PACKET, socket.SOCK_DGRAM,
socket.htons(0x800))
targ = sockaddr_ll()
@ -365,8 +388,9 @@ def check_reply(node, info, packet, sock, cfg, reqview):
targ.sll_halen = reqview[2]
targ.sll_protocol = socket.htons(0x800)
targ.sll_ifindex = info['netinfo']['ifidx']
pkt = ctypes.byref((ctypes.c_char * 256).from_buffer(repview))
sendto(tsock.fileno(), pkt, 256, 0, ctypes.byref(targ),
pkt = ctypes.byref((ctypes.c_char * 284).from_buffer(repview))
sendto(tsock.fileno(), pkt, 284, 0, ctypes.byref(targ),
ctypes.sizeof(targ))
print('Thinking about reply to {0}'.format(node))