fuzz: add a fuzz target for channel_id derivation

Signed-off-by: Antoine Poinsot <darosior@protonmail.com>

tests/fuzz/Makefile

@@ -15,6 +15,7 @@ FUZZ_COMMON_OBJS :=					\
 	common/bech32.o					\
 	common/bip32.o					\
 	common/bigsize.o				\
+	common/channel_id.o				\
 	common/json.o					\
 	common/json_stream.o				\
 	common/wireaddr.o				\

tests/fuzz/fuzz-channel_id.c

@@ -0,0 +1,70 @@
+#include <assert.h>
+#include <bitcoin/pubkey.h>
+#include <bitcoin/tx.h>
+#include <stdint.h>
+#include <string.h>
+#include <tests/fuzz/libfuzz.h>
+
+#include <ccan/tal/tal.h>
+#include <common/channel_id.h>
+#include <wire/wire.h>
+
+void init(int *argc, char ***argv)
+{
+}
+
+void run(const uint8_t *data, size_t size)
+{
+	struct channel_id chan_id;
+	struct pubkey basepoint_1, basepoint_2;
+	struct bitcoin_txid txid;
+	uint16_t vout;
+	const uint8_t **v1_chunks, **v2_chunks, **marshal_chunks;
+	const uint8_t *wire_ptr;
+	size_t wire_max;
+	uint8_t *wire_buf;
+
+	if (size < 34)
+		return;
+
+	/* 32 (txid) + 2 (vout ala LN) */
+	v1_chunks = get_chunks(NULL, data, size, 34);
+	for (size_t i = 0; i < tal_count(v1_chunks); i++) {
+		wire_ptr = v1_chunks[i];
+		wire_max = 32;
+		fromwire_bitcoin_txid(&wire_ptr, &wire_max, &txid);
+		assert(wire_ptr);
+		wire_max = 2;
+		vout = fromwire_u16(&wire_ptr, &wire_max);
+		derive_channel_id(&chan_id, &txid, vout);
+	}
+	tal_free(v1_chunks);
+
+	v2_chunks = get_chunks(NULL, data, size, PUBKEY_CMPR_LEN * 2);
+	for (size_t i = 0; i < tal_count(v2_chunks); i++) {
+		wire_ptr = v2_chunks[i];
+		wire_max = PUBKEY_CMPR_LEN;
+		fromwire_pubkey(&wire_ptr, &wire_max, &basepoint_1);
+		if (!wire_ptr)
+			continue;
+
+		wire_max = PUBKEY_CMPR_LEN;
+		fromwire_pubkey(&wire_ptr, &wire_max, &basepoint_2);
+		if (!wire_ptr)
+			continue;
+
+		derive_channel_id_v2(&chan_id, &basepoint_1, &basepoint_2);
+	}
+	tal_free(v2_chunks);
+
+	marshal_chunks = get_chunks(NULL, data, size, 32);
+	for (size_t i = 0; i < tal_count(marshal_chunks); i++) {
+		wire_ptr = marshal_chunks[i];
+		wire_max = tal_count(marshal_chunks[i]);
+		fromwire_channel_id(&wire_ptr, &wire_max, &chan_id);
+		wire_buf = tal_arr(NULL, uint8_t, tal_count(marshal_chunks[i]));
+		towire_channel_id(&wire_buf, &chan_id);
+		tal_free(wire_buf);
+	}
+	tal_free(marshal_chunks);
+}