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Fix spurious "Decryption key withheld" messages (#3061)
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When we receive an `m.unavailable` notification, do not show it as "Decryption
key withheld".
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@richvdh
richvdh authored Jan 13, 2023
1 parent 4847d78 commit eb058ed
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Showing 2 changed files with 150 additions and 60 deletions.
75 changes: 75 additions & 0 deletions spec/integ/megolm-integ.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1702,4 +1702,79 @@ describe("megolm", () => {
await Promise.all([sendPromise, megolmMessagePromise, aliceTestClient.httpBackend.flush("/keys/query", 1)]);
});
});

describe("m.room_key.withheld handling", () => {
// TODO: there are a bunch more tests for this sort of thing in spec/unit/crypto/algorithms/megolm.spec.ts.
// They should be converted to integ tests and moved.

it("does not block decryption on an 'm.unavailable' report", async function () {
await aliceTestClient.start();

// there may be a key downloads for alice
aliceTestClient.httpBackend.when("POST", "/keys/query").respond(200, {});
aliceTestClient.httpBackend.flush("/keys/query", 1, 5000);

// encrypt a message with a group session.
const groupSession = new Olm.OutboundGroupSession();
groupSession.create();
const messageEncryptedEvent = encryptMegolmEvent({
senderKey: testSenderKey,
groupSession: groupSession,
room_id: ROOM_ID,
});

// Alice gets the room message, but not the key
aliceTestClient.httpBackend.when("GET", "/sync").respond(200, {
next_batch: 1,
rooms: {
join: { [ROOM_ID]: { timeline: { events: [messageEncryptedEvent] } } },
},
});
await aliceTestClient.flushSync();

// alice will (eventually) send a room-key request
aliceTestClient.httpBackend.when("PUT", "/sendToDevice/m.room_key_request/").respond(200, {});
await aliceTestClient.httpBackend.flush("/sendToDevice/m.room_key_request/", 1, 1000);

// at this point, the message should be a decryption failure
const room = aliceTestClient.client.getRoom(ROOM_ID)!;
const event = room.getLiveTimeline().getEvents()[0];
expect(event.isDecryptionFailure()).toBeTruthy();

// we want to wait for the message to be updated, so create a promise for it
const retryPromise = new Promise((resolve) => {
event.once(MatrixEventEvent.Decrypted, (ev) => {
resolve(ev);
});
});

// alice gets back a room-key-withheld notification
aliceTestClient.httpBackend.when("GET", "/sync").respond(200, {
next_batch: 2,
to_device: {
events: [
{
type: "m.room_key.withheld",
sender: "@bob:example.com",
content: {
algorithm: "m.megolm.v1.aes-sha2",
room_id: ROOM_ID,
session_id: groupSession.session_id(),
sender_key: testSenderKey,
code: "m.unavailable",
reason: "",
},
},
],
},
});
await aliceTestClient.flushSync();

// the withheld notification should trigger a retry; wait for it
await retryPromise;

// finally: the message should still be a regular decryption failure, not a withheld notification.
expect(event.getContent().body).not.toContain("withheld");
});
});
});
135 changes: 75 additions & 60 deletions src/crypto/algorithms/megolm.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1613,76 +1613,91 @@ export class MegolmDecryption extends DecryptionAlgorithm {
const senderKey = content.sender_key;

if (content.code === "m.no_olm") {
const sender = event.getSender()!;
this.prefixedLogger.warn(`${sender}:${senderKey} was unable to establish an olm session with us`);
// if the sender says that they haven't been able to establish an olm
// session, let's proactively establish one
await this.onNoOlmWithheldEvent(event);
} else if (content.code === "m.unavailable") {
// this simply means that the other device didn't have the key, which isn't very useful information. Don't
// record it in the storage
} else {
await this.olmDevice.addInboundGroupSessionWithheld(
content.room_id,
senderKey,
content.session_id,
content.code,
content.reason,
);
}

// Note: after we record that the olm session has had a problem, we
// trigger retrying decryption for all the messages from the sender's
// Having recorded the problem, retry decryption on any affected messages.
// It's unlikely we'll be able to decrypt sucessfully now, but this will
// update the error message.
//
if (content.session_id) {
await this.retryDecryption(senderKey, content.session_id);
} else {
// no_olm messages aren't specific to a given megolm session, so
// we trigger retrying decryption for all the messages from the sender's
// key, so that we can update the error message to indicate the olm
// session problem.
await this.retryDecryptionFromSender(senderKey);
}
}

if (await this.olmDevice.getSessionIdForDevice(senderKey)) {
// a session has already been established, so we don't need to
// create a new one.
this.prefixedLogger.debug("New session already created. Not creating a new one.");
await this.olmDevice.recordSessionProblem(senderKey, "no_olm", true);
this.retryDecryptionFromSender(senderKey);
return;
}
let device = this.crypto.deviceList.getDeviceByIdentityKey(content.algorithm, senderKey);
private async onNoOlmWithheldEvent(event: MatrixEvent): Promise<void> {
const content = event.getContent();
const senderKey = content.sender_key;
const sender = event.getSender()!;
this.prefixedLogger.warn(`${sender}:${senderKey} was unable to establish an olm session with us`);
// if the sender says that they haven't been able to establish an olm
// session, let's proactively establish one

if (await this.olmDevice.getSessionIdForDevice(senderKey)) {
// a session has already been established, so we don't need to
// create a new one.
this.prefixedLogger.debug("New session already created. Not creating a new one.");
await this.olmDevice.recordSessionProblem(senderKey, "no_olm", true);
return;
}
let device = this.crypto.deviceList.getDeviceByIdentityKey(content.algorithm, senderKey);
if (!device) {
// if we don't know about the device, fetch the user's devices again
// and retry before giving up
await this.crypto.downloadKeys([sender], false);
device = this.crypto.deviceList.getDeviceByIdentityKey(content.algorithm, senderKey);
if (!device) {
// if we don't know about the device, fetch the user's devices again
// and retry before giving up
await this.crypto.downloadKeys([sender], false);
device = this.crypto.deviceList.getDeviceByIdentityKey(content.algorithm, senderKey);
if (!device) {
this.prefixedLogger.info(
"Couldn't find device for identity key " + senderKey + ": not establishing session",
);
await this.olmDevice.recordSessionProblem(senderKey, "no_olm", false);
this.retryDecryptionFromSender(senderKey);
return;
}
this.prefixedLogger.info(
"Couldn't find device for identity key " + senderKey + ": not establishing session",
);
await this.olmDevice.recordSessionProblem(senderKey, "no_olm", false);
return;
}
}

// XXX: switch this to use encryptAndSendToDevices() rather than duplicating it?
// XXX: switch this to use encryptAndSendToDevices() rather than duplicating it?

await olmlib.ensureOlmSessionsForDevices(this.olmDevice, this.baseApis, { [sender]: [device] }, false);
const encryptedContent: IEncryptedContent = {
algorithm: olmlib.OLM_ALGORITHM,
sender_key: this.olmDevice.deviceCurve25519Key!,
ciphertext: {},
[ToDeviceMessageId]: uuidv4(),
};
await olmlib.encryptMessageForDevice(
encryptedContent.ciphertext,
this.userId,
undefined,
this.olmDevice,
sender,
device,
{ type: "m.dummy" },
);
await olmlib.ensureOlmSessionsForDevices(this.olmDevice, this.baseApis, { [sender]: [device] }, false);
const encryptedContent: IEncryptedContent = {
algorithm: olmlib.OLM_ALGORITHM,
sender_key: this.olmDevice.deviceCurve25519Key!,
ciphertext: {},
[ToDeviceMessageId]: uuidv4(),
};
await olmlib.encryptMessageForDevice(
encryptedContent.ciphertext,
this.userId,
undefined,
this.olmDevice,
sender,
device,
{ type: "m.dummy" },
);

await this.olmDevice.recordSessionProblem(senderKey, "no_olm", true);
this.retryDecryptionFromSender(senderKey);
await this.olmDevice.recordSessionProblem(senderKey, "no_olm", true);

await this.baseApis.sendToDevice("m.room.encrypted", {
[sender]: {
[device.deviceId]: encryptedContent,
},
});
} else {
await this.olmDevice.addInboundGroupSessionWithheld(
content.room_id,
senderKey,
content.session_id,
content.code,
content.reason,
);
}
await this.baseApis.sendToDevice("m.room.encrypted", {
[sender]: {
[device.deviceId]: encryptedContent,
},
});
}

public hasKeysForKeyRequest(keyRequest: IncomingRoomKeyRequest): Promise<boolean> {
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