wallet: warn against accidental unsafe older() import

BIP 379 allows height and time locks that have no consensus meaning in BIP 68 / BIP 112.
This is used by some protocols like Lightning to encode extra data, but is unsafe when
used unintentionally. E.g. older(65536) is equivalent to older(1).

This commit emits a warning when importing such a descriptor.

It introduces a helper ForEachNode to traverse all miniscript nodes.

test/functional/wallet_importdescriptors.py

@@ -22,6 +22,7 @@ from test_framework.authproxy import JSONRPCException
 from test_framework.blocktools import COINBASE_MATURITY
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.descriptors import descsum_create
+from test_framework.script import SEQUENCE_LOCKTIME_TYPE_FLAG
 from test_framework.util import (
     assert_equal,
     assert_raises_rpc_error,
@@ -58,6 +59,7 @@ class ImportDescriptorsTest(BitcoinTestFramework):
         if 'warnings' in result[0]:
             observed_warnings = result[0]['warnings']
         assert_equal("\n".join(sorted(warnings)), "\n".join(sorted(observed_warnings)))
+        self.log.debug(result)
         assert_equal(result[0]['success'], success)
         if error_code is not None:
             assert_equal(result[0]['error']['code'], error_code)
@@ -783,5 +785,40 @@ class ImportDescriptorsTest(BitcoinTestFramework):
             assert_equal(w_multipath.getrawchangeaddress(address_type="bech32"), w_multisplit.getrawchangeaddress(address_type="bech32"))
         assert_equal(sorted(w_multipath.listdescriptors()["descriptors"], key=lambda x: x["desc"]), sorted(w_multisplit.listdescriptors()["descriptors"], key=lambda x: x["desc"]))
 
+        self.log.info("Test older() safety")
+
+        for flag in [0, SEQUENCE_LOCKTIME_TYPE_FLAG]:
+            self.log.debug("Importing a safe value always works")
+            safe_value = (65535 | flag)
+            self.test_importdesc(
+                {
+                    'desc': descsum_create(f"wsh(and_v(v:pk([12345678/0h/0h]{xpub}/*),older({safe_value})))"),
+                    'active': True,
+                    'range': [0, 2],
+                    'timestamp': 'now'
+                },
+                success=True
+            )
+
+            self.log.debug("Importing an unsafe value results in a warning")
+            unsafe_value = safe_value + 1
+            desc = descsum_create(f"wsh(and_v(v:pk([12345678/0h/0h]{xpub}/*),older({unsafe_value})))")
+            expected_warning = (
+                f"time-based relative locktime: older({unsafe_value}) > (65535 * 512) seconds is unsafe"
+                if flag == SEQUENCE_LOCKTIME_TYPE_FLAG
+                else f"height-based relative locktime: older({unsafe_value}) > 65535 blocks is unsafe"
+            )
+            self.test_importdesc(
+                {
+                    'desc': desc,
+                    'active': True,
+                    'range': [0, 2],
+                    'timestamp': 'now'
+                },
+                success=True,
+                warnings=[expected_warning],
+            )
+
+
 if __name__ == '__main__':
     ImportDescriptorsTest(__file__).main()