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dcerpc: mimic gap behavior for invalid data #14805

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dcerpc: mimic gap behavior for invalid data #14805

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79 changes: 49 additions & 30 deletions rust/src/dcerpc/dcerpc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -762,21 +762,20 @@ impl DCERPCState {
}
}

pub fn handle_input_data(&mut self, stream_slice: StreamSlice, direction: Direction) -> AppLayerResult {
let retval;
let mut cur_i = stream_slice.as_slice();
let mut consumed = 0u32;
let mut rem = cur_i.len() as u32;
fn handle_gap (&mut self, i: &[u8], direction: Direction, mimic: bool) -> (u32, i8) {
let mut consumed;

if !mimic && ((!self.ts_gap && !self.tc_gap) || ((self.ts_gap && direction == Direction::ToClient) || (self.tc_gap && direction == Direction::ToServer))) {
return (0, 0);
}
// Skip the record since this means that its in the middle of a known length record
if (self.ts_gap && direction == Direction::ToServer) || (self.tc_gap && direction == Direction::ToClient) {
SCLogDebug!("Trying to catch up after GAP (input {})", cur_i.len());
match self.search_dcerpc_record(cur_i) {
Ok((_, pg)) => {
SCLogDebug!("DCERPC record found");
let offset = cur_i.len() - pg.len();
cur_i = &cur_i[offset..];
consumed = offset as u32;
SCLogDebug!("Trying to catch up after GAP (input {})", i.len());
match self.search_dcerpc_record(i) {
Ok((_, pg)) => {
SCLogDebug!("DCERPC record found");
let offset = i.len() - pg.len();
consumed = offset as u32;
if !mimic {
match direction {
Direction::ToServer => {
self.ts_gap = false;
Expand All @@ -785,20 +784,36 @@ impl DCERPCState {
self.tc_gap = false;
}
}
},
_ => {
consumed = cur_i.len() as u32;
// At least 2 bytes are required to know if a new record is beginning
if consumed < 2 {
consumed = 0;
} else {
consumed -= 1;
}
SCLogDebug!("DCERPC record NOT found");
return AppLayerResult::incomplete(consumed, 2);
},
}
}
},
_ => {
consumed = i.len() as u32;
// At least 2 bytes are required to know if a new record is beginning
if consumed < 2 {
consumed = 0;
} else {
consumed -= 1;
}
SCLogDebug!("DCERPC record NOT found");
return (consumed, -1);
},
}

(consumed, 0)
}

pub fn handle_input_data(&mut self, stream_slice: StreamSlice, direction: Direction) -> AppLayerResult {
let retval;
let mut cur_i = stream_slice.as_slice();
let mut rem = cur_i.len() as u32;

SCLogDebug!("ts_gap: {:?}; direction: {:?}; tc_gap: {:?}", self.ts_gap, direction, self.tc_gap);
let (nb, ret) = self.handle_gap(cur_i, direction, false /* handling the actual gap */);
let mut consumed = nb;
if ret == -1 {
return AppLayerResult::incomplete(consumed, 2);
}
cur_i = &cur_i[consumed as usize..];
rem -= consumed;

let mut flow = std::ptr::null_mut();
Expand All @@ -817,7 +832,11 @@ impl DCERPCState {
header.rpc_vers,
header.rpc_vers_minor
);
return AppLayerResult::err();
SCLogDebug!("mimicing gap for invalid header");
let (nb, _ret) = self.handle_gap(cur_i, direction, true /* mimicing a gap */);
consumed += nb;
/* no need to update rem/cur_i as it won't be used anymore */
return AppLayerResult::incomplete(consumed, rem - consumed);
}
header
}
Expand Down Expand Up @@ -859,10 +878,10 @@ impl DCERPCState {

let hdrtype = hdr.hdrtype;

let _hdr = Frame::new(flow, &stream_slice, &cur_i[consumed as usize..], DCERPC_HDR_LEN as i64, DCERPCFrameType::Hdr as u8, None);
let _pdu = Frame::new(flow, &stream_slice, &cur_i[consumed as usize..], fraglen as i64, DCERPCFrameType::Pdu as u8, None);
let _hdr = Frame::new(flow, &stream_slice, cur_i, DCERPC_HDR_LEN as i64, DCERPCFrameType::Hdr as u8, None);
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@catenacyber catenacyber Feb 16, 2026

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Are you reverting fc9da1c which was incorrect as found by oss-fuzz
Am I understanding this correctly ?

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@inashivb inashivb Feb 16, 2026

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Are you reverting fc9da1c which was incorrect as found by oss-fuzz Am I understanding this correctly ?

No, I'm not reverting it. I'm creating the slice in the beginning now so it'll be wrong to index here at consumed. L816: https://github.com/OISF/suricata/pull/14805/files#diff-bb348f48dcbb4845f97a114f74772ee4849098c3254221826e5e0a61cbe35830R816

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@catenacyber catenacyber Feb 16, 2026

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This was already done at line 716
cur_i = &cur_i[offset..];
(with the line after being consumed = offset as u32; which is why fc9da1c is wrong)

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@inashivb inashivb Feb 17, 2026 •
edited
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I think you're right. I'm surprised fuzzers didn't catch that. Behavior in this PR looks correct to me. wdyt?

Edit: I think I misunderstood what you are saying in this thread. Are you referring to fuzzers finding the crash in #14766 and that being fixed here? Then, yes. I did not realize that the crash found by the fuzzers was not because of the new code.

let _pdu = Frame::new(flow, &stream_slice, cur_i, fraglen as i64, DCERPCFrameType::Pdu as u8, None);
if fraglen >= DCERPC_HDR_LEN && rem > DCERPC_HDR_LEN as u32 {
let _data = Frame::new(flow, &stream_slice, &cur_i[(consumed + DCERPC_HDR_LEN as u32) as usize..], (fraglen - DCERPC_HDR_LEN) as i64, DCERPCFrameType::Data as u8, None);
let _data = Frame::new(flow, &stream_slice, &cur_i[DCERPC_HDR_LEN as usize..], (fraglen - DCERPC_HDR_LEN) as i64, DCERPCFrameType::Data as u8, None);
}
let current_call_id = hdr.call_id;

Expand Down
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