Device keys signatures aren't propagated over federation

[S7evinK]

Description

/keys/signatures/upload doesn't seem to update the uploaded device_keys.signatures in the database or doesn't send it over federation.

Steps to reproduce

• Run Sytest with the changes from Add required fields to POST /keys/upload sytest#1197

The PR adds required fields (as per Spec 1.2) to the requests to /keys/upload, a subsequent call to /keys/signatures/upload doesn't seem to update the signatures, even though they're received by Synapse just fine.

From a local Sytest run:

not ok 8 uploading signed devices gets propagated over federation
# Started: 2022-02-24 16:14:06.239
# Ended: 2022-02-24 16:14:06.605
# Got "dSO80A01XiigH3uBiDVx/EjzaoycHcjq9lfQX0uWsqxl2giMIiSPR8a4d291W1ihKJL/a+myXS367WT6NAIcBA", expected "SJsl9W/rKOXWZ/ZEr9cP3oiWK5rv0G+Sb3kQ5D+TgGEt3Jyikb7/04wzBLoDOnjdhgS8MIC4dFvP24KgFFQyAQ" at {@anon-20220224_161359-13:localhost:8839}{ed25519:EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ} for  at tests/41end-to-end-keys/08-cross-signing.pl line 711.

2022-02-24 16:14:06,579 - synapse.rest.client.keys - 332 - INFO - POST-22 - uploaded signature: {'@anon-20220224_161359-13:localhost:8839': {'GZOQESIVQY': {'user_id': '@anon-20220224_161359-13:localhost:8839', 'signatures': {'@anon-20220224_161359-13:localhost:8839': {'ed25519:EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ': 'SJsl9W/rKOXWZ/ZEr9cP3oiWK5rv0G+Sb3kQ5D+TgGEt3Jyikb7/04wzBLoDOnjdhgS8MIC4dFvP24KgFFQyAQ'}}, 'device_id': 'GZOQESIVQY', 'keys': {'ed25519:GZOQESIVQY': 'MKkClRdltZlOHyCzxiDrm7MsDAsohXmAyeu2cYO6how', 'curve25519:GZOQESIVQY': 'IQ/Hu4GGOaxIpMavovFYGouVJeIP2miSfysv+Db3NXg'}, 'algorithms': ['m.olm.curve25519-aes-sha256', 'm.megolm.v1.aes-sha']}}}
2022-02-24 16:14:06,584 - synapse.access.https.8839 - 448 - INFO - POST-22 - 127.0.0.1 - 8839 - {@anon-20220224_161359-13:localhost:8839} Processed request: 0.004sec/0.001sec (0.001sec, 0.000sec) (0.001sec/0.001sec/3) 15B 200 "POST /_matrix/client/unstable/keys/signatures/upload?access_token=<redacted> HTTP/1.1" "Perl + Net::Async::HTTP/0.48" [0 dbevts]

Full logs can be found at https://github.com/matrix-org/sytest/actions/runs/1893676524

Version information

• Homeserver: None, discovered by Sytest

• Version: Develop as of 2022-02-24 14:56:24 Commit 41cf4c2

• Install method:

• Platform:

[erikjohnston]

This is because Synapse doesn't allow you to upload replace a different key with the same key ID:

synapse/synapse/handlers/e2e_keys.py

Lines 887 to 892 in e24ff8e

	if self_signing_key_id in stored_device.get("signatures", {}).get(
	user_id, {}
	):
	# we already have a signature on this device, so we
	# can skip it, since it should be exactly the same
	continue

We should probably return an entry in failures if the new key doesn't match the old key.