server.go: prevent partial mutation of currentNodeAnn in server.genNodeAnnouncement on netann.SignNodeAnnouncement failures

[mohamedawnallah]

Change Description

In this commit, we prevent partial mutation of the current node announcement during announcement signing. Previously, if node announcement signing failed, the current node announcement could become inconsistent.

Motivation and Context

This issue was discovered while working on issue #9455. Specifically, it was observed that:

• The enforcement of a single DNS hostname address related to Bolt 07 occurs in WriteNetAddrs.

• If there’s is an error, the error is correctly propagated from netann.SignNodeAnnouncement.

• However, part of the current node announcement (e.g., Addresses []net.Addr or CLI field uris from getinfo) was still being updated, leading to inconsistencies when inspecting with the command:

  lncli --network=regtest getinfo | jq '.uris'

Steps to Test

Steps for reviewers to follow to test the change.

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[MPins]

I haven’t found a good way to test this yet or assess the potential for announcement inconsistencies. If you have any suggestions on how to approach that, I’d be happy to try them out. That said, the change does seem to add robustness overall 👍

I also believe this change deserves a mention in the release notes.

[MPins]

nit: consider updating the comment to reflect that the node announcement isn’t being modified yet.

[mohamedawnallah]

I haven’t found a good way to test this yet or assess the potential for announcement inconsistencies. If you have any suggestions on how to approach that, I’d be happy to try them out. That said, the change does seem to add robustness overall 👍

Thanks for taking a look, @MPins! 🙏

This issue can be reproduced when SignNodeAnnouncement fails. This could potentially happen in any case where part of the logic returns an error in SignNodeAnnouncement.

You could simulate this error by:

1. Modifying the code to return an error at that point to simulate SignNodeAnnouncement failure.
2. Use any update announcement modifier like adding tcp address.
3. Observe that the node announcement fails to update, but the current in-memory state now contains that invalid address
4. Verify the inconsistent state by running lncli getinfo | jq ".uris" and seeing that tcp already there although the updatenodeannouncment RPC failed

Here are the relevant code references:

• lnd/server.go

  Lines 3463 to 3469 in cbdd1c2

  	// Sign a new update after applying all of the passed modifiers.
  	err := netann.SignNodeAnnouncement(
  	s.nodeSigner, s.identityKeyLoc, s.currentNodeAnn,
  	)
  	if err != nil {
  	return lnwire.NodeAnnouncement{}, err
  	}

• lnd/netann/node_announcement.go

  Lines 67 to 82 in cbdd1c2

  	// SignNodeAnnouncement signs the lnwire.NodeAnnouncement provided, which
  	// should be the most recent, valid update, otherwise the timestamp may not
  	// monotonically increase from the prior.
  	func SignNodeAnnouncement(signer lnwallet.MessageSigner,
  	keyLoc keychain.KeyLocator, nodeAnn *lnwire.NodeAnnouncement) error {
  	// Create the DER-encoded ECDSA signature over the message digest.
  	sig, err := SignAnnouncement(signer, keyLoc, nodeAnn)
  	if err != nil {
  	return err
  	}
  	// Parse the DER-encoded signature into a fixed-size 64-byte array.
  	nodeAnn.Signature, err = lnwire.NewSigFromSignature(sig)
  	return err
  	}

This issue regards partial mutation would become more obvious when we explicitly returns error here in WriteNetAddrs incase of user passing more than one DNS address which not allowed in bolt 7 as part of PR #9455.

func WriteNetAddrs(buf *bytes.Buffer, addresses []net.Addr) error {
...
case *DNSHostnameAddress:
    if dnsHostnameAddressFound {
        return errors.New("cannot advertise multiple " +
            "DNS hostname addresses. See Bolt 07")
    }
    if err := WriteDNSHostnameAddr(addrBuf, a); err != nil {
        return err
    }
    dnsHostnameAddressFound = true
}

This issue regards partial mutation would become more obvious when we explicitly returns error here in WriteNetAddrs incase of user passing more than one DNS address which not allowed in bolt 7 as part of PR #9455.

@ellemouton – What do you think about this?