fuzz: add a fuzz target for the close tx

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

tests/fuzz/Makefile

@@ -15,10 +15,13 @@ FUZZ_COMMON_OBJS :=					\
 	common/bech32.o					\
 	common/bip32.o					\
 	common/bigsize.o				\
+	common/close_tx.o				\
 	common/channel_id.o				\
+	common/permute_tx.o				\
 	common/json.o					\
 	common/json_stream.o				\
 	common/wireaddr.o				\
+	common/setup.o					\
 	common/type_to_string.o				\
 	common/utils.o					\
 	wire/fromwire.o					\

tests/fuzz/fuzz-close_tx.c

@@ -0,0 +1,92 @@
+#include <assert.h>
+#include <stdint.h>
+#include <string.h>
+#include <tests/fuzz/libfuzz.h>
+
+#include <bitcoin/pubkey.h>
+#include <bitcoin/chainparams.h>
+#include <bitcoin/script.h>
+#include <bitcoin/tx.h>
+#include <ccan/tal/tal.h>
+#include <common/amount.h>
+#include <common/close_tx.h>
+#include <common/setup.h>
+#include <common/utils.h>
+#include <wire/wire.h>
+
+void init(int *argc, char ***argv)
+{
+	common_setup("fuzzer");
+	chainparams = chainparams_for_network("bitcoin");
+}
+
+void run(const uint8_t *data, size_t size)
+{
+	const uint8_t *wire_ptr;
+	size_t wire_max, min_size, script_size;
+	struct bitcoin_txid txid;
+	uint32_t vout;
+	struct amount_sat funding, to_us, to_them, dust_limit, max;
+	const uint8_t *our_script, *their_script, *funding_script;
+	struct pubkey *pk1, *pk2;
+
+	/* create_close_tx wants:
+	 * - 3 scripts: 3 * N bytes
+	 * - 1 txid: 32 bytes
+	 * - 1 u32: 4 bytes
+	 * - 4 amount_sat: 4 * 8 bytes
+	 *
+	 * Since both output scripts size are not restricted, we also try
+	 * to vary their length.
+	 * Therefore, we allocate the entire remaining bytes to scripts.
+	 */
+	min_size = 8 * 3 + 4 + 32;
+	if (size < min_size + 2)
+		return;
+
+	script_size = (size - min_size) / 2;
+	wire_ptr = data;
+
+	wire_max = 8;
+	to_us = fromwire_amount_sat(&wire_ptr, &wire_max);
+	assert(wire_ptr);
+	wire_max = 8;
+	to_them = fromwire_amount_sat(&wire_ptr, &wire_max);
+	assert(wire_ptr);
+	wire_max = 8;
+	dust_limit = fromwire_amount_sat(&wire_ptr, &wire_max);
+	/* The funding must be > to_us + to_them (TODO: we could simulate some fees) .. */
+	if (!(amount_sat_add(&funding, to_us, to_them)))
+		return;
+	/* .. And < max_btc as we assert it's not nonsensical! */
+	max = AMOUNT_SAT((u32)WALLY_SATOSHI_PER_BTC * WALLY_BTC_MAX);
+	if (amount_sat_greater(funding, max)) {
+		funding = max;
+		to_us = amount_sat_div(max, 2);
+		to_them = amount_sat_div(max, 2);
+	}
+
+	wire_max = 4;
+	vout = fromwire_u32(&wire_ptr, &wire_max);
+	wire_max = 32;
+	fromwire_bitcoin_txid(&wire_ptr, &wire_max, &txid);
+
+	our_script = tal_dup_arr(tmpctx, const uint8_t, wire_ptr, script_size, 0);
+	their_script = tal_dup_arr(tmpctx, const uint8_t, wire_ptr + script_size,
+				   script_size, 0);
+
+	/* We assert it's valid, so we can't throw garbage at the funding script.. */
+	pk1 = tal(tmpctx, struct pubkey);
+	pk2 = tal(tmpctx, struct pubkey);
+	pubkey_from_hexstr("034fede2c619f647fe7c01d40ae22e4c285291ca2ffb47937bbfb7d6e8285a081f",
+			   PUBKEY_CMPR_LEN, pk1);
+	pubkey_from_hexstr("028dfe31019dd61fa04c76ad065410e5d063ac2949c04c14b214c1b363e517452f",
+			   PUBKEY_CMPR_LEN, pk2);
+	funding_script = bitcoin_redeem_2of2(tmpctx, pk1, pk2);
+
+	create_close_tx(tmpctx, chainparams, our_script,
+			their_script, funding_script, &txid,
+			vout, funding, to_us, to_them, dust_limit);
+
+	clean_tmpctx();
+}