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htlcswitch: for UpdateFailMalformedHTLC packets mark fail as needing conversion

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In this commit, we start the first phase of fixing an existing bug
within the switch. As is, we don't properly convert
`UpdateFailMalformedHTLC` to regular `UpdateFailHTLC` messages that are
fully encrypted. When we receive a `UpdateFailMalformedHTLC` today,
we'll convert it into a regular fail message by simply encoding the
failure message raw. This failure message doesn't have  a MAC yet, so if
we sent it backwards, then the destination wouldn't be able to decrypt
it. We can recognize this type of failure as it'll be the same size as
the raw failure message max size, but it has 4 extra bytes for the
encoding. When we come across this message, we'll mark is as needing
conversion so the switch can take care of it.
This commit is contained in:
Olaoluwa Osuntokun 2019-04-30 18:20:23 -07:00
parent 558c8ca2a8
commit 649e080da6
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GPG Key ID: CE58F7F8E20FD9A2
2 changed files with 23 additions and 1 deletions
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16
htlcswitch/link.go
View File

@ -2369,10 +2369,24 @@ func (l *channelLink) processRemoteSettleFails(fwdPkg *channeldb.FwdPkg,
outgoingHTLCID: pd.ParentIndex, outgoingHTLCID: pd.ParentIndex,
destRef: pd.DestRef, destRef: pd.DestRef,
htlc: &lnwire.UpdateFailHTLC{ htlc: &lnwire.UpdateFailHTLC{
Reason: lnwire.OpaqueReason(pd.FailReason), Reason: lnwire.OpaqueReason(
pd.FailReason,
),
}, },
} }
// If the failure message lacks an HMAC (but includes
// the 4 bytes for encoding the message and padding
// lengths, then this means that we received it as an
// UpdateFailMalformedHTLC. As a result, we'll signal
// that we need to convert this error within the switch
// to an actual error, by encrypting it as if we were
// the originating hop.
convertedErrorSize := lnwire.FailureMessageLength + 4
if len(pd.FailReason) == convertedErrorSize {
failPacket.convertedError = true
}
// Add the packet to the batch to be forwarded, and // Add the packet to the batch to be forwarded, and
// notify the overflow queue that a spare spot has been // notify the overflow queue that a spare spot has been
// freed up within the commitment state. // freed up within the commitment state.

8
htlcswitch/packet.go
View File

@ -61,6 +61,14 @@ type htlcPacket struct {
// encrypted with any shared secret. // encrypted with any shared secret.
localFailure bool localFailure bool
// convertedError is set to true if this is an HTLC fail that was
// created using an UpdateFailMalformedHTLC from the remote party. If
// this is true, then when forwarding this failure packet, we'll need
// to wrap it as if we were the first hop if it's a multi-hop HTLC. If
// it's a direct HTLC, then we'll decode the error as no encryption has
// taken place.
convertedError bool
// hasSource is set to true if the incomingChanID and incomingHTLCID // hasSource is set to true if the incomingChanID and incomingHTLCID
// fields of a forwarded fail packet are already set and do not need to // fields of a forwarded fail packet are already set and do not need to
// be looked up in the circuit map. // be looked up in the circuit map.