fix(legacy): limit EthereumGetPublicKey allowable paths

legacy/firmware/fsm_msg_coin.h

@@ -35,6 +35,11 @@ void fsm_msgGetPublicKey(const GetPublicKey *msg) {
     curve = msg->ecdsa_curve_name;
   }
 
+  // XXX note to future developers:
+  // If more path restrictions are added here, don't forget to also check
+  // EthereumGetPublicKey in particular for whether it's possible to go around
+  // the new restrictions that way.
+
   // UnlockPath is required to access SLIP25 paths.
   if (msg->address_n_count > 0 && msg->address_n[0] == PATH_SLIP25_PURPOSE) {
     // Verify that the desired path lies in the unlocked subtree.

legacy/firmware/fsm_msg_ethereum.h

@@ -75,6 +75,17 @@ void fsm_msgEthereumGetPublicKey(const EthereumGetPublicKey *msg) {
   const CoinInfo *coin = fsm_getCoin(true, "Bitcoin");
   if (!coin) return;
 
+  // Only allow m/44' and m/45' subtrees. This allows usage with _any_ SLIP-44
+  // (Ethereum or otherwise), plus the Casa multisig subtree. Anything else must
+  // go through (a) GetPublicKey or (b) a dedicated coin-specific message.
+  if (!msg->address_n_count || (msg->address_n[0] != (44 | PATH_HARDENED) &&
+                                msg->address_n[0] != (45 | PATH_HARDENED))) {
+    fsm_sendFailure(FailureType_Failure_DataError,
+                    _("Invalid path for EthereumGetPublicKey"));
+    layoutHome();
+    return;
+  }
+
   const char *curve = coin->curve_name;
   uint32_t fingerprint;
   HDNode *node = fsm_getDerivedNode(curve, msg->address_n, msg->address_n_count,

tests/device_tests/ethereum/test_getpublickey.py

@@ -18,6 +18,7 @@ import pytest
 
 from trezorlib import ethereum
 from trezorlib.debuglink import TrezorClientDebugLink as Client
+from trezorlib.exceptions import TrezorFailure
 from trezorlib.tools import parse_path
 
 from ...common import parametrize_using_common_fixtures
@@ -35,3 +36,16 @@ def test_ethereum_getpublickey(client: Client, parameters, result):
     assert res.node.chain_code.hex() == result["chain_code"]
     assert res.node.public_key.hex() == result["public_key"]
     assert res.xpub == result["xpub"]
+
+
+def test_slip25_disallowed(client: Client):
+    path = parse_path("m/10025'/60'/0'/0/0")
+    with pytest.raises(TrezorFailure):
+        ethereum.get_public_node(client, path)
+
+
+@pytest.mark.skip_t2
+def test_legacy_restrictions(client: Client):
+    path = parse_path("m/46'")
+    with pytest.raises(TrezorFailure, match="Invalid path for EthereumGetPublicKey"):
+        ethereum.get_public_node(client, path)

tests/ui_tests/fixtures.json

@@ -408,6 +408,8 @@
 "T1_ethereum-test_getpublickey.py::test_ethereum_getpublickey[parameters0-result0]": "37e446e17465ce9823c34c9162d94e4ad3c84faa86bae7966c753be5c5fd77a2",
 "T1_ethereum-test_getpublickey.py::test_ethereum_getpublickey[parameters1-result1]": "37e446e17465ce9823c34c9162d94e4ad3c84faa86bae7966c753be5c5fd77a2",
 "T1_ethereum-test_getpublickey.py::test_ethereum_getpublickey[parameters2-result2]": "37e446e17465ce9823c34c9162d94e4ad3c84faa86bae7966c753be5c5fd77a2",
+"T1_ethereum-test_getpublickey.py::test_legacy_restrictions": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+"T1_ethereum-test_getpublickey.py::test_slip25_disallowed": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
 "T1_ethereum-test_sign_typed_data.py::test_ethereum_sign_typed_data_blind[array_of_structs]": "04b94ca842aa77fdc6b75b07bbe178c4ea99c35e6dae630588fa5d9cb67b9090",
 "T1_ethereum-test_sign_typed_data.py::test_ethereum_sign_typed_data_blind[bare_minimum]": "730a5d3bf1389ac14aec7ee9f65e2cbf516957e5077acc0e07a7541f667e2f0b",
 "T1_ethereum-test_sign_typed_data.py::test_ethereum_sign_typed_data_blind[basic_data]": "fd99dc685a4a125db0f3f8d2a16ffa242bd57e4ff714d66cc9c4161c486f53be",
@@ -1481,6 +1483,7 @@
 "TT_ethereum-test_getpublickey.py::test_ethereum_getpublickey[parameters0-result0]": "66d489ec9fc951219d16eb4ed51f966510df137eabba5df68a3bd50b42cc1d1a",
 "TT_ethereum-test_getpublickey.py::test_ethereum_getpublickey[parameters1-result1]": "66d489ec9fc951219d16eb4ed51f966510df137eabba5df68a3bd50b42cc1d1a",
 "TT_ethereum-test_getpublickey.py::test_ethereum_getpublickey[parameters2-result2]": "66d489ec9fc951219d16eb4ed51f966510df137eabba5df68a3bd50b42cc1d1a",
+"TT_ethereum-test_getpublickey.py::test_slip25_disallowed": "80a6e289138a604cf351a29511cf6f85e2243591317894703152787e1351a1a3",
 "TT_ethereum-test_sign_typed_data.py::test_ethereum_sign_typed_data[array_of_structs]": "d8915973909efac6657a87d8369bffe91cb280ff8fcec0bec79a63a8256ebc34",
 "TT_ethereum-test_sign_typed_data.py::test_ethereum_sign_typed_data[bare_minimum]": "91fd7f2a1d5fdfdc45a9060930178ce749c11f62c079b13da6e38c154267fa67",
 "TT_ethereum-test_sign_typed_data.py::test_ethereum_sign_typed_data[basic_data]": "779ed1029d6810bca189456c46fa35ff2a958aba0207b4f49738d4b2fa8f9414",