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Ilya bakhtin/dns dcerpc reversed v5 #12503

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Ilya bakhtin/dns dcerpc reversed v5 #12503

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fffefcf
protodetect/dcerpc: improve DCERPC UDP probing parser
ilya-bakhtin Jul 21, 2024
317b93c
protodetect: simplify code since DCERPC UDP detection is improved
ilya-bakhtin Jul 21, 2024
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4 changes: 3 additions & 1 deletion rust/src/dcerpc/dcerpc_udp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -300,9 +300,11 @@ pub unsafe extern "C" fn rs_dcerpc_udp_get_tx_cnt(vtx: *mut std::os::raw::c_void
/// Probe input to see if it looks like DCERPC.
fn probe(input: &[u8]) -> (bool, bool) {
match parser::parse_dcerpc_udp_header(input) {
Ok((_, hdr)) => {
Ok((leftover_bytes, hdr)) => {
let is_request = hdr.pkt_type == 0x00;
let is_dcerpc = hdr.rpc_vers == 0x04 &&
hdr.fragnum == 0 &&
leftover_bytes.len() >= hdr.fraglen as usize &&
(hdr.flags2 & 0xfc == 0) &&
(hdr.drep[0] & 0xee == 0) &&
(hdr.drep[1] <= 3);
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25 changes: 5 additions & 20 deletions src/app-layer-detect-proto.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1408,7 +1408,6 @@ AppProto AppLayerProtoDetectGetProto(AppLayerProtoDetectThreadCtx *tctx, Flow *f
(flags & STREAM_TOSERVER) ? "toserver" : "toclient");

AppProto alproto = ALPROTO_UNKNOWN;
AppProto pm_alproto = ALPROTO_UNKNOWN;

if (!FLOW_IS_PM_DONE(f, flags)) {
AppProto pm_results[g_alproto_max];
Expand All @@ -1426,38 +1425,24 @@ AppProto AppLayerProtoDetectGetProto(AppLayerProtoDetectThreadCtx *tctx, Flow *f
FLOW_RESET_PP_DONE(f, reverse_dir);
}
}

/* HACK: if detected protocol is dcerpc/udp, we run PP as well
* to avoid misdetecting DNS as DCERPC. */
if (!(ipproto == IPPROTO_UDP && alproto == ALPROTO_DCERPC))
goto end;

pm_alproto = alproto;

/* fall through */
SCReturnUInt(alproto);
}
}

if (!FLOW_IS_PP_DONE(f, flags)) {
bool rflow = false;
alproto = AppLayerProtoDetectPPGetProto(f, buf, buflen, ipproto, flags, &rflow);
DEBUG_VALIDATE_BUG_ON(*reverse_flow);
alproto = AppLayerProtoDetectPPGetProto(f, buf, buflen, ipproto, flags, reverse_flow);
if (AppProtoIsValid(alproto)) {
if (rflow) {
*reverse_flow = true;
}
goto end;
SCReturnUInt(alproto);
}
}

/* Look if flow can be found in expectation list */
if (!FLOW_IS_PE_DONE(f, flags)) {
DEBUG_VALIDATE_BUG_ON(*reverse_flow);
alproto = AppLayerProtoDetectPEGetProto(f, flags);
}

end:
if (!AppProtoIsValid(alproto))
alproto = pm_alproto;

SCReturnUInt(alproto);
}

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