bolt4

commit 2a99b5c9df493f27989383f9b0fef80fb78b0569
parent 501b5455752bd45997c9fa5d747ff67c52ebb10e
Author: Jared Tobin <jared@jtobin.io>
Date:   Sat, 10 Oct 2026 13:35:04 +0400

lib: harden TLV decoding

decodeTlv converted the record length to Int before checking it, so
a length of 2^64 - 1 wrapped to -1, passed the bounds check and
decoded as an empty value. Compare in Word64 instead.

Unknown even TLV types must cause a failure. decodeHopPayload kept
them in hpUnknownTlvs and decodeBlindedHopData skipped them; both now
fail. Hop payload types 16 (payment_metadata) and 18
(total_amount_msat) are defined by the spec but not yet typed, so they
are still accepted into hpUnknownTlvs.

Diffstat:
M
lib/Lightning/Protocol/BOLT4/Blinding.hs
 | 
5
++++-
M
lib/Lightning/Protocol/BOLT4/Codec.hs
 | 
16
++++++++++++----
M
lib/Lightning/Protocol/BOLT4/Types.hs
 | 
2
+-

3 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/lib/Lightning/Protocol/BOLT4/Blinding.hs b/lib/Lightning/Protocol/BOLT4/Blinding.hs
@@ -209,6 +209,8 @@ encodeBlindedHopData !bhd = encodeTlvStream (buildTlvs bhd)
 {-# INLINE encodeBlindedHopData #-}
 
 -- | Decode TLV stream to BlindedHopData.
+--
+-- Fails on unknown even TLV types; unknown odd types are skipped.
 decodeBlindedHopData :: BS.ByteString -> Maybe BlindedHopData
 decodeBlindedHopData !bs = do
   tlvs <- decodeTlvStream bs
@@ -238,7 +240,8 @@ parseBlindedHopData = go emptyHopData
         pc <- decodePaymentConstraints val
         go bhd { bhdPaymentConstraints = Just pc } rest
       14 -> go bhd { bhdAllowedFeatures = Just val } rest
-      _  -> go bhd rest  -- Skip unknown TLVs
+      _  | even typ -> Nothing
+         | otherwise -> go bhd rest
 
 -- PaymentRelay encoding/decoding --------------------------------------------
 
diff --git a/lib/Lightning/Protocol/BOLT4/Codec.hs b/lib/Lightning/Protocol/BOLT4/Codec.hs
@@ -125,11 +125,12 @@ decodeTlv :: BS.ByteString -> Maybe (TlvRecord, BS.ByteString)
 decodeTlv !bs = do
   (typ, r1) <- decodeBigSize bs
   (len, r2) <- decodeBigSize r1
-  let !len' = fromIntegral len
-  if BS.length r2 < len'
+  -- compare in Word64 so that large lengths cannot wrap
+  if len > fromIntegral (BS.length r2)
     then Nothing
     else do
-      let !val = BS.take len' r2
+      let !len' = fromIntegral len
+          !val = BS.take len' r2
           !rest = BS.drop len' r2
       Just (TlvRecord typ val, rest)
 {-# INLINE decodeTlv #-}
@@ -199,6 +200,10 @@ encodeHopPayload !hp = encodeTlvStream (buildTlvs hp)
       in  amt' ++ cltv' ++ sci' ++ pd' ++ ed' ++ cpk' ++ unk
 
 -- | Decode HopPayload from bytes.
+--
+-- Fails on unknown even TLV types. Types 16 (payment_metadata) and 18
+-- (total_amount_msat) are accepted and kept, with unknown odd types,
+-- in 'hpUnknownTlvs'.
 decodeHopPayload :: BS.ByteString -> Maybe HopPayload
 decodeHopPayload !bs = do
   tlvs <- decodeTlvStream bs
@@ -227,7 +232,10 @@ parseHopPayload = go emptyHop
         go hp { hpPaymentData = Just pd } rest
       10 -> go hp { hpEncryptedData = Just val } rest
       12 -> go hp { hpCurrentPathKey = Just val } rest
-      _  -> go hp { hpUnknownTlvs = TlvRecord typ val : hpUnknownTlvs hp } rest
+      _  | even typ && typ /= 16 && typ /= 18 -> Nothing
+         | otherwise ->
+             go hp { hpUnknownTlvs = TlvRecord typ val : hpUnknownTlvs hp }
+                rest
 
 -- ShortChannelId -----------------------------------------------------------
 
diff --git a/lib/Lightning/Protocol/BOLT4/Types.hs b/lib/Lightning/Protocol/BOLT4/Types.hs
@@ -163,7 +163,7 @@ data HopPayload = HopPayload
   , hpPaymentData    :: !(Maybe PaymentData)    -- ^ TLV type 8
   , hpEncryptedData  :: !(Maybe BS.ByteString)  -- ^ TLV type 10
   , hpCurrentPathKey :: !(Maybe BS.ByteString)  -- ^ TLV type 12
-  , hpUnknownTlvs    :: ![TlvRecord]            -- ^ Unknown types
+  , hpUnknownTlvs    :: ![TlvRecord]            -- ^ 16, 18 and unknown odd
   } deriving (Eq, Show, Generic)
 
 -- | Payment data for final hop (TLV type 8).