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protodetect: improve DCERPC UDP probing parser and simplify app-layer-detect-proto.c code #11541

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protodetect: improve DCERPC UDP probing parser and simplify app-layer-detect-proto.c code #11541

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protodetect/dcerpc: improve dcerpc udp probe
ilya-bakhtin Jul 21, 2024
05bd7e9
protodetect: simplify app-layer-detect-proto.c code since DCERPC UDP …
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 @@ -294,9 +294,11 @@ 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 &&
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Why this condition leftover_bytes.len() >= hdr.fraglen as usize ?

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Please see the conventional parser code at rust/src/dcerpc/dcerpc_udp.rs:207
The probe must do at least the same since the DCERPC PM is extremely short.

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Ok indeed, we are on UDP here :-)

(hdr.flags2 & 0xfc == 0) &&
(hdr.drep[0] & 0xee == 0) &&
(hdr.drep[1] <= 3);
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