fix: typed data with a missing field or a bool that is not true or false is refused (closes #552)

ethers signs a bool field by whether its value is truthy, so the string
"false" was shown as false and signed as true, and a bool field left out
was shown as nothing and signed as false. The sign screen now refuses
typed data whose message leaves out a declared field, at any level of
nesting, or holds a bool that is not true or false: the error line names
the field and Sign is disabled. The background refuses a signature for it
too. Presence is an own-key test, so a field named like a built-in
property such as constructor is not found by accident. signedPrimaryType()
moves to the shared module so the background reads the message as the
same type.

Model: opus-5-5

README.md

@@ -2182,6 +2182,13 @@ view would leave a wallet one click from deletion.
     - Typed data that states no primary type, or one other than the type it
       would be signed as, or that cannot be read → shown with the error line
       saying so and "Sign" disabled; only "Reject" remains
+    - Typed data whose message leaves out a field its type declares, at any
+      level of nesting, or gives a `bool` field a value other than `true` or
+      `false` → shown with the error line naming the field and "Sign" disabled;
+      only "Reject" remains. ethers signs a `bool` by whether its value is
+      truthy, so the string `"false"` would be signed as true and a field left
+      out as false. The background refuses such a signature too and answers the
+      site with the same sentence
     - Typed data whose domain `chainId` names a chain other than the active
       network's → shown with the error line naming both chain ids and "Sign"
       disabled; only "Reject" remains. EIP-712 asks for this, because the

src/background/index.js

@@ -22,6 +22,8 @@ const { debugFetch, log } = require("../shared/log");
 const {
     verifySignedTx,
     verifySignature,
+    signedPrimaryType,
+    typedDataMessageRefusal,
     typedDataChainRefusal,
     failureIsRetryable,
     describeTxFailure,
@@ -1787,18 +1789,27 @@ runtime.onMessage.addListener((msg, sender, sendResponse) => {
                     signature,
                     approval.approvedFrom,
                 );
-                // The sign screen refuses typed data whose domain names
-                // another chain. A signature for it that arrives anyway is
-                // refused here, against the network active now.
+                // The sign screen refuses typed data whose message ethers
+                // would sign differently from how it is shown, or whose
+                // domain names another chain. A signature for it that arrives
+                // anyway is refused here, against the network active now.
                 const sp = approval.signParams;
                 if (
                     sp.method === "eth_signTypedData_v4" ||
                     sp.method === "eth_signTypedData"
                 ) {
-                    const refusal = typedDataChainRefusal(
-                        JSON.parse(sp.typedData).domain,
-                        networkById(s.networkId),
-                    );
+                    const data = JSON.parse(sp.typedData);
+                    const refusal =
+                        typedDataMessageRefusal(
+                            data.types,
+                            signedPrimaryType(data.types),
+                            data.message,
+                            "",
+                        ) ||
+                        typedDataChainRefusal(
+                            data.domain,
+                            networkById(s.networkId),
+                        );
                     if (refusal) throw new ApprovalMismatchError(refusal);
                 }
                 settleApproval(msg.id, { signature }, { holdsClaim: true });

src/popup/views/approval.js

@@ -27,7 +27,6 @@ const {
     Interface,
     MaxUint256,
     toUtf8String,
-    TypedDataEncoder,
 } = require("ethers");
 const { getPrice, formatUsd } = require("../../shared/prices");
 const { ERC20_ABI } = require("../../shared/constants");
@@ -48,6 +47,8 @@ const { getSignerForAddress } = require("../../shared/wallet");
 const { walletDefect } = require("../../shared/walletDefects");
 const {
     describeSigningFailure,
+    signedPrimaryType,
+    typedDataMessageRefusal,
     typedDataChainRefusal,
 } = require("../../shared/approvalVerify");
 const txStatus = require("./txStatus");
@@ -432,22 +433,12 @@ function markInvisibleCharacters(text) {
         );
 }
 
-// The type ethers will sign typed data as. ethers does not read the page's
-// `primaryType`: it takes the one struct in `types` that no other struct
-// refers to. Throws when the types name no such single struct, which ethers
-// would refuse to sign as well.
-function signedPrimaryType(types) {
-    const structs = { ...types };
-    // ethers derives EIP712Domain itself and rejects it as an input.
-    delete structs.EIP712Domain;
-    return TypedDataEncoder.getPrimaryType(structs);
-}
-
 // Why a signature request cannot be signed, as a sentence for the error line,
 // or null when it can. Only typed data is refused: the `primaryType` the page
 // states has to be the type ethers will sign, or this screen would name one
-// message while another is signed. Its domain may name no chain but the active
-// network's.
+// message while another is signed. Its message has to hold every declared
+// field, with each `bool` true or false, and its domain may name no chain but
+// the active network's.
 function typedDataRefusal(sp) {
     if (sp.method === "personal_sign" || sp.method === "eth_sign") return null;
     let data;
@@ -470,7 +461,10 @@ function typedDataRefusal(sp) {
             ", so it cannot be signed."
         );
     }
-    return typedDataChainRefusal(data.domain, currentNetwork());
+    return (
+        typedDataMessageRefusal(data.types, signed, data.message, "") ||
+        typedDataChainRefusal(data.domain, currentNetwork())
+    );
 }
 
 // The largest amount a Permit2 allowance can hold, a uint160. Permit2 treats

src/shared/approvalVerify.js

@@ -56,6 +56,7 @@ const {
     getBigInt,
     getBytes,
     toQuantity,
+    TypedDataEncoder,
     verifyMessage,
     verifyTypedData,
 } = require("ethers");
@@ -636,6 +637,63 @@ function verifySignature(signParams, signature, expectedFrom) {
     return recovered;
 }
 
+// The type ethers will sign typed data as. ethers does not read the page's
+// `primaryType`: it takes the one struct in `types` that no other struct
+// refers to. Throws when the types name no such single struct, which ethers
+// would refuse to sign as well.
+function signedPrimaryType(types) {
+    const structs = { ...types };
+    // ethers derives EIP712Domain itself and rejects it as an input.
+    delete structs.EIP712Domain;
+    return TypedDataEncoder.getPrimaryType(structs);
+}
+
+// Why a typed data message cannot be signed as the screen shows it, as a
+// sentence, or null when it can. ethers signs a `bool` field by whether its
+// value is truthy, so the string "false" is signed as true and a field left
+// out as false. Each field that `type` declares, at every level of nesting,
+// must be one of the value's own keys, and each `bool` must be true or false.
+// Called with the type ethers signs, the message, and a `path` of "".
+function typedDataMessageRefusal(types, type, value, path) {
+    const itemType = type.replace(/\[\d*\]$/, "");
+    if (itemType !== type) {
+        // ethers refuses to sign a list field that is not a list.
+        if (!Array.isArray(value)) return null;
+        for (let i = 0; i < value.length; i++) {
+            const refusal = typedDataMessageRefusal(
+                types,
+                itemType,
+                value[i],
+                `${path}[${i}]`,
+            );
+            if (refusal) return refusal;
+        }
+        return null;
+    }
+    if (type === "bool" && value !== true && value !== false) {
+        return `The field "${path}" is not true or false, so this typed data cannot be signed.`;
+    }
+    for (const field of types[type] || []) {
+        const at = path ? `${path}.${field.name}` : field.name;
+        // An own key only: a plain lookup of `constructor` finds a function.
+        const present =
+            value !== null &&
+            typeof value === "object" &&
+            Object.prototype.hasOwnProperty.call(value, field.name);
+        if (!present) {
+            return `The field "${at}" is missing from the message, so this typed data cannot be signed.`;
+        }
+        const refusal = typedDataMessageRefusal(
+            types,
+            field.type,
+            value[field.name],
+            at,
+        );
+        if (refusal) return refusal;
+    }
+    return null;
+}
+
 // Why typed data cannot be signed while `network` is the active network, as a
 // sentence, or null when it can. EIP-712 has a wallet refuse typed data whose
 // domain names another chain, because the signature is valid on that chain.
@@ -824,6 +882,8 @@ function describeSigningFailure(response, fallbackMessage) {
 module.exports = {
     verifySignedTx,
     verifySignature,
+    signedPrimaryType,
+    typedDataMessageRefusal,
     typedDataChainRefusal,
     assertNoForbiddenFields,
     assertNothingUnchecked,

tests/backgroundApproval.test.js

@@ -384,13 +384,13 @@ function loadBackground(options) {
 
     // The same through eth_signTypedData_v4, whose params name the address
     // first and the typed data second.
-    function requestTypedData() {
+    function requestTypedData(typedData = TYPED_DATA) {
         let rpcResult = null;
         messageListener(
             {
                 type: "AUTISTMASK_RPC",
                 method: "eth_signTypedData_v4",
-                params: [signer.address, TYPED_DATA],
+                params: [signer.address, typedData],
             },
             { origin: ORIGIN },
             (r) => {
@@ -1494,8 +1494,8 @@ describe("what the approval is verified against", () => {
     // screen; a signature for it that reaches the background anyway is not
     // handed to the page (https://git.eeqj.de/sneak/AutistMask/issues/519).
     // TYPED_DATA names mainnet.
-    async function answerTypedData(bg, pending) {
-        const { domain, types, message } = JSON.parse(TYPED_DATA);
+    async function answerTypedData(bg, pending, typedData = TYPED_DATA) {
+        const { domain, types, message } = JSON.parse(typedData);
         delete types.EIP712Domain;
         const signature = await signer.signTypedData(domain, types, message);
         const answer = bg.send(
@@ -1539,6 +1539,42 @@ describe("what the approval is verified against", () => {
         expect(pending.result()).toEqual({ error: { message: refusal } });
     });
 
+    // ethers signs a `bool` field sent as the string "false" as true, and one
+    // left out as false. The sign screen refuses both; a signature for either
+    // that reaches the background anyway is not handed to the page
+    // (https://git.eeqj.de/sneak/AutistMask/issues/552).
+    test.each([
+        [
+            '"false"',
+            "false",
+            'The field "approved" is not true or false, so this typed data cannot be signed.',
+        ],
+        [
+            "left out",
+            undefined,
+            'The field "approved" is missing from the message, so this typed data cannot be signed.',
+        ],
+    ])(
+        "typed data with a bool %s is refused, not handed back",
+        async (_, approved, refusal) => {
+            const data = JSON.parse(TYPED_DATA);
+            data.types.Note.push({ name: "approved", type: "bool" });
+            data.message.approved = approved;
+            const typedData = JSON.stringify(data);
+            const bg = loadBackground();
+            const pending = bg.requestTypedData(typedData);
+            await settle();
+
+            const { answer } = await answerTypedData(bg, pending, typedData);
+
+            expect(answer.sendResponse).toHaveBeenCalledWith({
+                error: refusal,
+                retryable: false,
+            });
+            expect(pending.result()).toEqual({ error: { message: refusal } });
+        },
+    );
+
     test("a sign request from another address raises no approval at all", async () => {
         const bg = loadBackground();
         const pending = bg.requestSign(other.address);

tests/typedDataPermit.test.js

@@ -28,7 +28,7 @@ globalThis.chrome = {
     storage: { local: { get: async () => ({}), set: async () => {} } },
 };
 
-const { getAddress, MaxUint256 } = require("ethers");
+const { getAddress, MaxUint256, TypedDataEncoder } = require("ethers");
 const { state } = require("../src/shared/state");
 const { decryptWithPassword } = require("../src/shared/vault");
 const approval = require("../src/popup/views/approval");
@@ -662,3 +662,107 @@ describe("the sign screen refuses typed data for another chain", () => {
         expect(node("btn-approve-sign").disabled).toBe(false);
     });
 });
+
+// ethers signs a `bool` field by whether its value is truthy in JavaScript:
+// the string "false" is signed as true, and a field left out as false. The
+// screen would show one value while another is signed, so such typed data is
+// refused, and so is any declared field left out of the message
+// (https://git.eeqj.de/sneak/AutistMask/issues/552). DAI's older permit
+// declares the `bool` field `allowed`.
+describe("the sign screen refuses a message ethers would sign differently", () => {
+    const NOT_A_BOOL =
+        'The field "allowed" is not true or false, so this typed data cannot be signed.';
+    const MISSING =
+        'The field "allowed" is missing from the message, so this typed data cannot be signed.';
+
+    function daiPermit(allowed) {
+        return { ...DAI_PERMIT, message: { ...DAI_PERMIT.message, allowed } };
+    }
+
+    const withoutAllowed = {
+        ...DAI_PERMIT,
+        message: { ...DAI_PERMIT.message },
+    };
+    delete withoutAllowed.message.allowed;
+
+    beforeEach(() => {
+        decryptWithPassword.mockClear();
+    });
+
+    test('ethers signs "false" as true, and a bool left out as false', () => {
+        const hash = (data) =>
+            TypedDataEncoder.hash(
+                data.domain,
+                { Permit: data.types.Permit },
+                data.message,
+            );
+        expect(hash(daiPermit("false"))).toBe(hash(daiPermit(true)));
+        expect(hash(withoutAllowed)).toBe(hash(daiPermit(false)));
+    });
+
+    test('a bool sent as the string "false" shows the error, with Sign disabled', async () => {
+        await openSignScreen(daiPermit("false"));
+        expect(node("approve-sign-error").textContent).toBe(NOT_A_BOOL);
+        expect(node("btn-approve-sign").disabled).toBe(true);
+    });
+
+    test("a bool left out shows the error, with Sign disabled", async () => {
+        await openSignScreen(withoutAllowed);
+        expect(node("approve-sign-error").textContent).toBe(MISSING);
+        expect(node("btn-approve-sign").disabled).toBe(true);
+    });
+
+    test("Sign clicked anyway decrypts and signs nothing", async () => {
+        const sent = await openSignScreen(daiPermit("false"));
+        node("approve-sign-password").value = "any password";
+        await click("btn-approve-sign");
+
+        expect(decryptWithPassword).not.toHaveBeenCalled();
+        expect(sent.map((msg) => msg.type)).not.toContain(
+            "AUTISTMASK_SIGN_RESPONSE",
+        );
+        expect(node("approve-sign-error").textContent).toBe(NOT_A_BOOL);
+    });
+
+    test("a well-formed message leaves Sign enabled", async () => {
+        for (const allowed of [true, false]) {
+            await openSignScreen(daiPermit(allowed));
+            expect(node("approve-sign-error").textContent).toBe("");
+            expect(node("btn-approve-sign").disabled).toBe(false);
+        }
+    });
+
+    test("a field left out inside a list item is named by its place", () => {
+        const [first, second] = PERMIT_BATCH.message.details;
+        const withoutNonce = { ...second };
+        delete withoutNonce.nonce;
+        const data = {
+            ...PERMIT_BATCH,
+            message: {
+                ...PERMIT_BATCH.message,
+                details: [first, withoutNonce],
+            },
+        };
+        expect(typedDataRefusal(request(data))).toBe(
+            'The field "details[1].nonce" is missing from the message, so this typed data cannot be signed.',
+        );
+    });
+
+    // A plain lookup of a field named after a built-in object property reads
+    // back a function, which ethers would sign as true.
+    test("a field named after a built-in object property is missing when left out", () => {
+        const data = {
+            ...LOGIN,
+            types: {
+                ...LOGIN.types,
+                Login: [
+                    ...LOGIN.types.Login,
+                    { name: "constructor", type: "bool" },
+                ],
+            },
+        };
+        expect(typedDataRefusal(request(data))).toBe(
+            'The field "constructor" is missing from the message, so this typed data cannot be signed.',
+        );
+    });
+});