net_processing: Ignore MSG_WITNESS_TX entries from INV messages #35920

ajtowns commented at 8:41 PM on August 6, 2026: contributor

When introducing wtxidrelay we added checks to skip attempts to announce txs with the wrong hash (https://github.com/bitcoin/bitcoin/pull/18044#discussion_r403953004), but didn't similarly ignore MSG_WITNESS_TX entries in announcements, which have never been valid (see BIP-144).

This PR corrects that oversight, skipping such announcements. It also moves the check to be after the disconnect code, so that attempting to announce txs on fRelay=false doesn't get treated as okay just because you're doing it wrong. As a result this allows deduping the seen_tx_hashes set.

DrahtBot commented at 8:41 PM on August 6, 2026: contributor

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35920.

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ajtowns commented at 8:56 PM on August 6, 2026: contributor

See also #35917 and #35878 (review)

l0rinc commented at 9:02 PM on August 6, 2026: contributor

Concept ACK, thanks for pushing a fix for #35878 (review). If you touch again, please add me as coauthor.

ajtowns renamed this:
~~net_processing: Ignore MSG_TX_WITNESS entries from INV messages~~
net_processing: Ignore MSG_WITNESS_TX entries from INV messages
on Aug 6, 2026

DrahtBot closed this on Aug 7, 2026

DrahtBot reopened this on Aug 7, 2026

in src/net_processing.cpp:4383 in eaaea13cda

4381 | +                // This ignores any MSG_WITNESS_TX entries, as that inv
4382 | +                // type is only for use with GETDATA (per BIP 144).
4383 | +                if (peer.m_wtxid_relay) {
4384 | +                    if (!inv.IsMsgWtx()) continue;
4385 | +                } else {
4386 | +                    if (!inv.IsMsgTx()) continue;

darosior commented at 9:01 PM on August 7, 2026:

Ignoring MSG_WITNESS_TX for wtxid relay peers seems fine, because i expect wtxid relay codebases to be newer / better maintained, and because BIP 339 explicitly states:

After a node has received a wtxidrelay message from a peer, the node MUST use the MSG_WTX inv type when announcing transactions to that peer.

However for txid relay peers, i'm afraid we are in a similar situation to unannounced transaction processing. We have supported it for a decade, and while it Is Incorrect, i'm afraid there may be an unmaintained codebase out there that relies on it. It's a bit more niche than unannounced transaction processing, but still, i think we should have some evidence this isn't being used in the wild before dropping support.

ajtowns commented at 1:26 AM on August 8, 2026:

Based on the got inv debug.log lines, my lots-of-peers node received no witness-tx invs in April-July, versus:

Month	block	tx	wtx
April	3,210	6,935,321	1,174,811,061
May	2,092	3,530,619	854,676,397
June	1,783	13,683,220	1,793,970,323
July	1,924	10,870,284	2,474,162,561

Numbers from:

zstdcat debug.log-202604*.zst | grep got.inv: | cut -d\  -f5 |
  awk '{c[$0]++} END {for (l in c) printf "%8d %s\n", c[l], l}'

ajtowns commented at 3:19 AM on August 12, 2026:

For people who do find instances of this, grep got.inv:.witness-tx .bitcoin/debug.log should indicate the txid being sent, as well as whether your peer already had the tx in question ("have" vs "new").

fjahr commented at 1:50 PM on August 11, 2026: contributor

Concept ACK

0xB10C commented at 3:02 PM on August 12, 2026: contributor

As per https://bnoc.xyz/t/any-reachable-node-receiving-tx-announcement-via-msg-witness-tx/159/5: /btcwire:0.5.0/neutrino:0.12.0-beta/ seems to be announcing transactions with InvTypeWitnessTx:

https://github.com/lightninglabs/neutrino/blob/c96685a023c6946be7d463541b49e0f37f527982/query.go#L951-L969

ajtowns commented at 9:47 PM on August 12, 2026: contributor

As per https://bnoc.xyz/t/any-reachable-node-receiving-tx-announcement-via-msg-witness-tx/159/5: /btcwire:0.5.0/neutrino:0.12.0-beta/ seems to be announcing transactions with InvTypeWitnessTx:

https://github.com/lightninglabs/neutrino/blob/c96685a023c6946be7d463541b49e0f37f527982/query.go#L951-L969

Filed as https://github.com/lightninglabs/neutrino/issues/384

net_processing: Ignore MSG_WITNESS_TX entries in inv messages

BIP 144 specifies that MSG_WITNESS_TX is "only for use in getdata",
so if we receive it anyway, ignore it, rather than treating it as a
by-txid announcement.

Also changes the code ordering so that attempting to announce txs on a
connection where tx relay is disabled triggers a disconnect, even if we
would have ignored the announcement for being the wrong inv type.

2eefc296d4

tests: Check we disconnect on tx INVs on blocks-only conns

Previously we only checked disconnection occurs on "correct" announcements
(WTX on a wtxidrelay connection); extend that to checking all possible
announcements (still only on a wtxidrelay connection).

a24f315175

net_processing: Combine seen_txids and seen_wtxids

After the previous commit only one of these will ever be used
for any particular INV message, so there's no need for two.

Co-Authored-By: Antoine Poinsot <mail@antoinep.com>

0f9bffe6e1

ajtowns force-pushed on Aug 12, 2026

ajtowns commented at 10:09 PM on August 12, 2026: contributor

Changed to allow witness-tx in invs for non-wtxidrelay peers. Lame.

Concept ACK, thanks for pushing a fix for #35878 (comment). If you touch again, please add me as coauthor.

I didn't copy any code from you, and I'm not even sure what this is in regards to. Nothing here is substantive enough to be worth arguing about authorship.