`UserIdentity::has_verification_violation` does not work for our own identity

[richvdh]

#3795 added a new method UserIdentity::has_verification_violation.

However, it appears to have omitted support for tracking verification of the user's own identity. This means that if our own identity was rotated, and a new device added, signed by the new identity, we would share messages to that device despite there being no evidence it is not controlled by an attacker.

This will become less of a problem in future, when we refuse to do any operations without our own identity being verified, but in the meantime it is a security hole, and, for as long as matrix-sdk-crypto has support for sending messages without verifying our identity, it will remain a footgun. I think it therefore needs fixing as a prerequisite to #3793.

[BillCarsonFr]

This means that if our own identity was rotated, and a new device added, signed by the new identity, we would share messages to that device despite there being no evidence it is not controlled by an attacker.

This is not true with OnlySigned isolation mode, the sending will fail until you verified the new identity:

matrix-rust-sdk/crates/matrix-sdk-crypto/src/session_manager/group_sessions/share_strategy.rs

Lines 245 to 249 in 17370a5

	Some(identity) if !identity.is_verified() => {
	return Err(OlmError::SessionRecipientCollectionError(
	SessionRecipientCollectionError::SendingFromUnverifiedDevice,
	))
	}

[richvdh]

This is not true with OnlySigned isolation mode, the sending will fail until you verified the new identity:

Yeah. I've slightly forgotten what all this was about, but I think it was mostly about CollectStrategy::DeviceBasedStrategy (ie, the strategy used in AllDevicesIsolationMode):

This will become less of a problem in future, when we refuse to do any operations without our own identity being verified, but in the meantime it is a security hole, and, for as long as matrix-sdk-crypto has support for sending messages without verifying our identity, it will remain a footgun.