Hi,
I'm working on dissecting a proprietary protocol that extends Bluetooth HCI_ACL
with a LUA dissector. As there's no heuristics dissector list registered for
this particular protocol I thought something similar could be achieved with a
chained dissector. I retrieve the original HCI_ACL dissector handle and replace
it with my own LUA dissector. In LUA dissector apply some heuristics and if
it's not my own protocol then call the original HCI_ACL dissector via the
handle.
Code looks like this:
local proto_test = Proto("test", "Use chaining as heuristic dissector")
local proto_default_acl
function is_test_proto(tvb, pinfo)
-- Apply heuristics to determine if own protocol
return false
end
function proto_test.dissector(tvb, pinfo, tree)
if not is_test_proto(tvb, pinfo) then
return proto_default_acl:call(tvb, pinfo, tree)
end
pinfo.cols.protocol = "test"
tree = tree:add(proto_test, tvb)
return tvb:len()
end
function proto_test.init()
local hci_type = DissectorTable.get("hci_h4.type")
local pattern = 0x02 -- ACL
proto_default_acl = hci_type:get_dissector(pattern)
hci_type:add(pattern, proto_test)
end
This unfortunately did not work and I was not able to find out why until I
started looking at the HCI_ACL dissector code itself.
static gint
dissect_bthci_acl(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void
*data)
{
<...>
/* Reject the packet if data is NULL */
if (data == NULL)
return 0;
The above NULL check is hit for all calls coming from the LUA dissector. The
LUA dissector function prototype does not have the data parameter and it
appears it's simply lost when chaining calls through LUA.
Any suggestions on how to approach this? Would it be possible to extend the LUA
dissector interface with another function prototype that supports the data
parameter? Just support relaying the parameter in chained dissectors, not
modifying or doing any fancy stuff with it.
/Mikael
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