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Have the peer and target info on DHCP receive

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This has the data that will be handy in formulating a reply.
This commit is contained in:
Jarrod Johnson 2020-03-09 14:39:53 -04:00
parent 934f8f0f20
commit f20fb70336
1 changed files with 32 additions and 4 deletions
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36
confluent_server/confluent/discovery/protocols/pxe.py
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@ -57,6 +57,12 @@ class in_pktinfo(ctypes.Structure): # from bits/in.h
('ipi_spec_dst', in_addr),
('ipi_addr', in_addr)]
class sockaddr_in(ctypes.Structure):
_fields_ = [('sin_family', ctypes.c_ushort), # per bits/sockaddr.h
('sin_port', ctypes.c_uint16), # per netinet/in.h
('sin_addr', in_addr)]
recvmsg = libc.recvmsg
recvmsg.argtypes = [ctypes.c_int, ctypes.POINTER(msghdr), ctypes.c_int]
recvmsg.restype = ctypes.c_size_t
@ -79,6 +85,7 @@ def CMSG_SPACE(length): # bits/socket.h
cmsgtype = ctypes.c_char * CMSG_SPACE(ctypes.sizeof(in_pktinfo)).value
cmsgsize = CMSG_SPACE(ctypes.sizeof(in_pktinfo)).value
pxearchs = {
'\x00\x00': 'bios-x86',
@ -170,6 +177,9 @@ def find_info_in_options(rq, optidx):
vivso = {'service-type': 'cumulus-switch', 'arch': arch}
return uuid, arch, vivso
def ipfromint(numb):
return socket.inet_ntoa(struct.pack('I', numb))
def snoop(handler, protocol=None):
#TODO(jjohnson2): ipv6 socket and multicast for DHCPv6, should that be
#prominent
@ -185,10 +195,12 @@ def snoop(handler, protocol=None):
ready = select.select([net4], [], [], None)
if not ready or not ready[0]:
continue
clientaddr = sockaddr_in()
rawbuffer = bytearray(2048)
data = pkttype.from_buffer(rawbuffer)
msg = msghdr()
cmsg = cmsgtype()
cmsgarr = bytearray(cmsgsize)
cmsg = cmsgtype.from_buffer(cmsgarr)
iov = iovec()
iov.iov_base = ctypes.addressof(data)
iov.iov_len = 2048
@ -196,16 +208,32 @@ def snoop(handler, protocol=None):
msg.msg_iovlen = 1
msg.msg_control = ctypes.addressof(cmsg)
msg.msg_controllen = ctypes.sizeof(cmsg)
msg.msg_name = ctypes.addressof(clientaddr)
msg.msg_namelen = ctypes.sizeof(clientaddr)
# We'll leave name and namelen blank for now
i = recvmsg(net4.fileno(), ctypes.pointer(msg), 0)
rq = memoryview(rawbuffer)
rq = rq[:i]
# if we have a small packet, just skip, it can't possible hold enough
# data and avoids some downstream IndexErrors that would be messy
# with try/except
if i < 64:
continue
rq = bytearray(rq)
peer = ipfromint(clientaddr.sin_addr.s_addr)
_, level, typ = struct.unpack('QII', cmsgarr[:16])
if level == socket.IPPROTO_IP and typ == IP_PKTINFO:
idx, recv, targ = struct.unpack('III', cmsgarr[16:28])
recv = ipfromint(recv)
targ = ipfromint(targ)
# peer is the source ip (in dhcpdiscover, 0.0.0.0)
# recv is the 'ip' that recevied the packet, regardless of target
# targ is the ip in the destination ip of the header.
# idx is the ip link number of the receiving nic
# For example, a DHCPDISCOVER will probably have:
# peer of 0.0.0.0
# targ of 255.255.255.255
# recv of <actual ip address that could reply>
# idx correlated to the nic
rq = memoryview(rawbuffer)
rq = bytearray(rq[:i])
if rq[0] == 1: # Boot request
addrlen = rq[2]
if addrlen > 16 or addrlen == 0: