* Pull out GetUserDirectoryTables helper
* Don't rebuild the dir in tests that don't need it
In #10796 I changed registering a user to add directory entries under.
This means we don't have to force a directory regbuild in to tests of
the user directory search.
* Move test_initial to tests/storage
* Add type hints to both test_user_directory files
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
* Factor more stuff out of `_get_events_and_persist`
It turns out that the event-sorting algorithm in `_get_events_and_persist` is
also useful in other circumstances. Here we move the current
`_auth_and_persist_fetched_events` to `_auth_and_persist_fetched_events_inner`,
and then factor the sorting part out to `_auth_and_persist_fetched_events`.
* `_get_remote_auth_chain_for_event`: remove redundant `outlier` assignment
`get_event_auth` returns events with the outlier flag already set, so this is
redundant (though we need to update a test where `get_event_auth` is mocked).
* `_get_remote_auth_chain_for_event`: move existing-event tests earlier
Move a couple of tests outside the loop. This is a bit inefficient for now, but
a future commit will make it better. It should be functionally identical.
* `_get_remote_auth_chain_for_event`: use `_auth_and_persist_fetched_events`
We can use the same codepath for persisting the events fetched as part of an
auth chain as for those fetched individually by `_get_events_and_persist` for
building the state at a backwards extremity.
* `_get_remote_auth_chain_for_event`: use a dict for efficiency
`_auth_and_persist_fetched_events` sorts the events itself, so we no longer
need to care about maintaining the ordering from `get_event_auth` (and no
longer need to sort by depth in `get_event_auth`).
That means that we can use a map, making it easier to filter out events we
already have, etc.
* changelog
* `_auth_and_persist_fetched_events`: improve docstring
* Improve typing in user_directory files
This makes the user_directory.py in storage pass most of mypy's
checks (including `no-untyped-defs`). Unfortunately that file is in the
tangled web of Store class inheritance so doesn't pass mypy at the moment.
The handlers directory has already been mypyed.
Co-authored-by: reivilibre <olivier@librepush.net>
Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>
Co-authored-by: reivilibre <olivier@librepush.net>
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
It's a simplification, but one that'll help make the user directory logic easier
to follow with the other changes upcoming. It's not strictly required for those
changes, but this will help simplify the resulting logic that listens for
`m.room.member` events and generally make the logic easier to follow.
This means the config option `search_all_users` ends up controlling the
search query only, and not the data we store. The cost of doing so is an
extra row in the `user_directory` and `user_directory_search` tables for
each local user which
- belongs to no public rooms
- belongs to no private rooms of size ≥ 2
I think the cost of this will be marginal (since they'll already have entries
in `users` and `profiles` anyway).
As a small upside, a homeserver whose directory was built with this
change can toggle `search_all_users` without having to rebuild their
directory.
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
This updates the ordering of the returned events from the spaces
summary API to that defined in MSC2946 (which updates MSC1772).
Previously a step was skipped causing ordering to be inconsistent with
clients.
Turns out that the functionality added in #10546 to skip TLS was incompatible
with older Twisted versions, so we need to be a bit more inventive.
Also, add a test to (hopefully) not break this in future. Sadly, testing TLS is
really hard.
As opposed to only allowing the summary of spaces which the user is
already in or has world-readable visibility.
This makes the logic consistent with whether a space/room is returned
as part of a space and whether a space summary can start at a space.
If a room which the requesting user was invited to was queried over
federation it will now properly appear in the spaces summary (instead
of being stripped out by the requesting server).
If there are no services providing a protocol, omit it completely
instead of returning an empty dictionary.
This fixes a long-standing spec compliance bug.
Reproducible on a federated homeserver when there is a membership auth event as a floating outlier. Then when we try to backfill one of that persons messages, it has missing membership auth to fetch which caused us to mistakenly replace the `context` for the message with that of the floating membership `outlier` event. Since `outliers` have no `state` or `state_group`, the error bubbles up when we continue down the persisting route: `sqlite3.IntegrityError: NOT NULL constraint failed: event_to_state_groups.state_group`
Call stack:
```
backfill
_auth_and_persist_event
_check_event_auth
_update_auth_events_and_context_for_auth
```
==============================
Bugfixes
--------
- Fix a bug introduced in Synapse 1.38 which caused an exception at startup when SAML authentication was enabled. ([\#10477](https://github.com/matrix-org/synapse/issues/10477))
- Fix a long-standing bug where Synapse would not inform clients that a device had exhausted its one-time-key pool, potentially causing problems decrypting events. ([\#10485](https://github.com/matrix-org/synapse/issues/10485))
- Fix reporting old R30 stats as R30v2 stats. Introduced in v1.39.0rc1. ([\#10486](https://github.com/matrix-org/synapse/issues/10486))
Internal Changes
----------------
- Fix an error which prevented the Github Actions workflow to build the docker images from running. ([\#10461](https://github.com/matrix-org/synapse/issues/10461))
- Fix release script to correctly version debian changelog when doing RCs. ([\#10465](https://github.com/matrix-org/synapse/issues/10465))
-----BEGIN PGP SIGNATURE-----
iQFEBAABCgAuFiEEBTGR3/RnAzBGUif3pULk7RsPrAkFAmEBUJUQHGVyaWtAbWF0
cml4Lm9yZwAKCRClQuTtGw+sCWi6CACfA3B7rXfQIO893mctSZkNhtAG/e4o310M
etvjAtovKmKeFqBvm89FPmFoXvGA2ypoz7Jz2fdkP56DNKIXvihnDc8EeQ3gGawf
hQ8GBjICOL1e7R/4qzuOCWYdppBGoGNAbz7qyxAUxZ/XOzsPJ2VBGkgyXWZkyPe/
nJYsuMuMp117HUwTqPqs3oZuTN0MRTy6xgaDfbFbcX9UC/amLmGIWOhlme8iV15r
HQAW0X7F2Un5h7eQwogWTDb9gBHKnJ4ApaSJLfZl9E72i0Sv7o9UFcLIdy2DRVSq
gxlRBVzVU6ZndCQ4vQXFSjQ20VGNXc2vpKVRE1D6YXxmxVNbBQB4
=lb6H
-----END PGP SIGNATURE-----
Merge tag 'v1.39.0rc3' into develop
Synapse 1.39.0rc3 (2021-07-28)
==============================
Bugfixes
--------
- Fix a bug introduced in Synapse 1.38 which caused an exception at startup when SAML authentication was enabled. ([\#10477](https://github.com/matrix-org/synapse/issues/10477))
- Fix a long-standing bug where Synapse would not inform clients that a device had exhausted its one-time-key pool, potentially causing problems decrypting events. ([\#10485](https://github.com/matrix-org/synapse/issues/10485))
- Fix reporting old R30 stats as R30v2 stats. Introduced in v1.39.0rc1. ([\#10486](https://github.com/matrix-org/synapse/issues/10486))
Internal Changes
----------------
- Fix an error which prevented the Github Actions workflow to build the docker images from running. ([\#10461](https://github.com/matrix-org/synapse/issues/10461))
- Fix release script to correctly version debian changelog when doing RCs. ([\#10465](https://github.com/matrix-org/synapse/issues/10465))
Previously only world-readable rooms were shown. This means that
rooms which are public, knockable, or invite-only with a pending invitation,
are included in a space summary. It also applies the same logic to
the experimental room version from MSC3083 -- if a user has access
to the proper allowed rooms then it is shown in the spaces summary.
This change is made per MSC3173 allowing stripped state of a room to
be shown to any potential room joiner.
The idea here is to stop people sending things that aren't joins/leaves/knocks through these endpoints: previously you could send anything you liked through them. I wasn't able to find any security holes from doing so, but it doesn't sound like a good thing.
This implements refresh tokens, as defined by MSC2918
This MSC has been implemented client side in Hydrogen Web: vector-im/hydrogen-web#235
The basics of the MSC works: requesting refresh tokens on login, having the access tokens expire, and using the refresh token to get a new one.
Signed-off-by: Quentin Gliech <quentingliech@gmail.com>
If a room is remote and we don't have a user in it, always try to join it. It might fail if the room is invite-only, but we don't have a user to invite with, so at this point it's the best we can do.
Fixes#10233 (at least to some extent)
This could cause a minor data leak if someone defined a non-restricted join rule
with an allow key or used a restricted join rule in an older room version, but this is
unlikely.
Additionally this starts adding unit tests to the spaces summary handler.
This PR adds a common configuration section for all modules (see docs). These modules are then loaded at startup by the homeserver. Modules register their hooks and web resources using the new `register_[...]_callbacks` and `register_web_resource` methods of the module API.
Fixes#1834.
`get_new_events_for_appservice` internally calls `get_events_as_list`, which will filter out any rejected events. If all returned events are filtered out, `_notify_interested_services` will return without updating the last handled stream position. If there are 100 consecutive such events, processing will halt altogether.
Breaking the loop is now done by checking whether we're up-to-date with `current_max` in the loop condition, instead of relying on an empty `events` list.
Signed-off-by: Willem Mulder <14mRh4X0r@gmail.com>
https://github.com/matrix-org/synapse/issues/9962 uncovered that we accidentally removed all but one of the presence updates that we store in the database when persisting multiple updates. This could cause users' presence state to be stale.
The bug was fixed in #10014, and this PR just adds a test that failed on the old code, and was used to initially verify the bug.
The test attempts to insert some presence into the database in a batch using `PresenceStore.update_presence`, and then simply pulls it out again.
This should help ensure that equivalent results are achieved between
homeservers querying for the summary of a space.
This implements modified MSC1772 rules, according to MSC2946.
The different is that the origin_server_ts of the m.room.create event
is not used as a tie-breaker since this might not be known if the
homeserver is not part of the room.
Part of #9744
Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.
`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>`
At the moment, if you'd like to share presence between local or remote users, those users must be sharing a room together. This isn't always the most convenient or useful situation though.
This PR adds a module to Synapse that will allow deployments to set up extra logic on where presence updates should be routed. The module must implement two methods, `get_users_for_states` and `get_interested_users`. These methods are given presence updates or user IDs and must return information that Synapse will use to grant passing presence updates around.
A method is additionally added to `ModuleApi` which allows triggering a set of users to receive the current, online presence information for all users they are considered interested in. This is the equivalent of that user receiving presence information during an initial sync.
The goal of this module is to be fairly generic and useful for a variety of applications, with hard requirements being:
* Sending state for a specific set or all known users to a defined set of local and remote users.
* The ability to trigger an initial sync for specific users, so they receive all current state.
Fixes https://github.com/matrix-org/synapse/issues/9572
When a SSO user logs in for the first time, we create a local Matrix user for them. This goes through the register_user flow, which ends up triggering the spam checker. Spam checker modules don't currently have any way to differentiate between a user trying to sign up initially, versus an SSO user (whom has presumably already been approved elsewhere) trying to log in for the first time.
This PR passes `auth_provider_id` as an argument to the `check_registration_for_spam` function. This argument will contain an ID of an SSO provider (`"saml"`, `"cas"`, etc.) if one was used, else `None`.
This great big stack of commits is a a whole load of hoop-jumping to make it easier to store additional values in login tokens, and then to actually store the SSO Identity Provider in the login token. (Making use of that data will follow in a subsequent PR.)
This PR attempts to eliminate unnecessary presence sending work when your local server joins a room, or when a remote server joins a room your server is participating in by processing state deltas in chunks rather than individually.
---
When your server joins a room for the first time, it requests the historical state as well. This chunk of new state is passed to the presence handler which, after filtering that state down to only membership joins, will send presence updates to homeservers for each join processed.
It turns out that we were being a bit naive and processing each event individually, and sending out presence updates for every one of those joins. Even if many different joins were users on the same server (hello IRC bridges), we'd send presence to that same homeserver for every remote user join we saw.
This PR attempts to deduplicate all of that by processing the entire batch of state deltas at once, instead of only doing each join individually. We process the joins and note down which servers need which presence:
* If it was a local user join, send that user's latest presence to all servers in the room
* If it was a remote user join, send the presence for all local users in the room to that homeserver
We deduplicate by inserting all of those pending updates into a dictionary of the form:
```
{
server_name1: {presence_update1, ...},
server_name2: {presence_update1, presence_update2, ...}
}
```
Only after building this dict do we then start sending out presence updates.
This PR adds a homeserver config option, `user_directory.prefer_local_users`, that when enabled will show local users higher in user directory search results than remote users. This option is off by default.
Note that turning this on doesn't necessarily mean that remote users will always be put below local users, but they should be assuming all other ranking factors (search query match, profile information present etc) are identical.
This is useful for, say, University networks that are openly federating, but want to prioritise local students and staff in the user directory over other random users.
Add off-by-default configuration settings to:
- disable putting an invitee's profile info in invite events
- disable profile lookup via federation
Signed-off-by: Andrew Ferrazzutti <fair@miscworks.net>
- Update black version to the latest
- Run black auto formatting over the codebase
- Run autoformatting according to [`docs/code_style.md
`](80d6dc9783/docs/code_style.md)
- Update `code_style.md` docs around installing black to use the correct version
This is the final step for supporting multiple OIDC providers concurrently.
First of all, we reorganise the config so that you can specify a list of OIDC providers, instead of a single one. Before:
oidc_config:
enabled: true
issuer: "https://oidc_provider"
# etc
After:
oidc_providers:
- idp_id: prov1
issuer: "https://oidc_provider"
- idp_id: prov2
issuer: "https://another_oidc_provider"
The old format is still grandfathered in.
With that done, it's then simply a matter of having OidcHandler instantiate a new OidcProvider for each configured provider.
* make the OIDC bits of the test work at a higher level - via the REST api instead of poking the OIDCHandler directly.
* Move it to test_login.py, where I think it fits better.
Again in preparation for handling more than one OIDC provider, add a new caveat to the macaroon used as an OIDC session cookie, which remembers which OIDC provider we are talking to. In future, when we get a callback, we'll need it to make sure we talk to the right IdP.
As part of this, I'm adding an idp_id and idp_name field to the OIDC configuration object. They aren't yet documented, and we'll just use the old values by default.
The idea here is that we will have an instance of OidcProvider for each
configured IdP, with OidcHandler just doing the marshalling of them.
For now it's still hardcoded with a single provider.
Some light refactoring of OidcHandler, in preparation for bigger things:
* remove inheritance from deprecated BaseHandler
* add an object to hold the things that go into a session cookie
* factor out a separate class for manipulating said cookies
SynapseRequest is in danger of becoming a bit of a dumping-ground for "useful stuff relating to Requests",
which isn't really its intention (its purpose is to override render, finished and connectionLost to set up the
LoggingContext and write the right entries to the request log).
Putting utility functions inside SynapseRequest means that lots of our code ends up requiring a
SynapseRequest when there is nothing synapse-specific about the Request at all, and any old
twisted.web.iweb.IRequest will do. This increases code coupling and makes testing more difficult.
In short: move get_user_agent out to a utility function.
The final part (for now) of my work to implement a username picker in synapse itself. The idea is that we allow
`UsernameMappingProvider`s to return `localpart=None`, in which case, rather than redirecting the browser
back to the client, we redirect to a username-picker resource, which allows the user to enter a username.
We *then* complete the SSO flow (including doing the client permission checks).
The static resources for the username picker itself (in
https://github.com/matrix-org/synapse/tree/rav/username_picker/synapse/res/username_picker)
are essentially lifted wholesale from
https://github.com/matrix-org/matrix-synapse-saml-mozilla/tree/master/matrix_synapse_saml_mozilla/res.
As the comment says, we might want to think about making them customisable, but that can be a follow-up.
Fixes#8876.
Fixes a bug that deactivated users appear in the directory when their profile information was updated.
To change profile information of deactivated users is neccesary for example you will remove displayname or avatar.
But they should not appear in directory. They are deactivated.
Co-authored-by: Erik Johnston <erikj@jki.re>
This is another part of my work towards fixing #8876. It moves some of the logic currently in the SAML and OIDC handlers - in particular the call to `AuthHandler.complete_sso_login` down into the `SsoHandler`.
* move simple_async_mock to test_utils
... so that it can be re-used
* Remove references to `SamlHandler._map_saml_response_to_user` from tests
This method is going away, so we can no longer use it as a test point. Instead,
factor out a higher-level method which takes a SAML object, and verify correct
behaviour by mocking out `AuthHandler.complete_sso_login`.
* changelog
* Remove references to handler._auth_handler
(and replace them with hs.get_auth_handler)
* Factor out a utility function for building Requests
* Remove mocks of `OidcHandler._map_userinfo_to_user`
This method is going away, so mocking it out is no longer a valid approach.
Instead, we mock out lower-level methods (eg _remote_id_from_userinfo), or
simply allow the regular implementation to proceed and update the expectations
accordingly.
* Remove references to `OidcHandler._map_userinfo_to_user` from tests
This method is going away, so we can no longer use it as a test point. Instead
we build mock "callback" requests which we pass into `handle_oidc_callback`,
and verify correct behaviour by mocking out `AuthHandler.complete_sso_login`.
==============================
Bugfixes
--------
- Fix a regression in v1.24.0rc1 which failed to allow SAML mapping providers which were unable to redirect users to an additional page. ([\#8878](https://github.com/matrix-org/synapse/issues/8878))
Internal Changes
----------------
- Add support for the `prometheus_client` newer than 0.9.0. Contributed by Jordan Bancino. ([\#8875](https://github.com/matrix-org/synapse/issues/8875))
-----BEGIN PGP SIGNATURE-----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=is1Y
-----END PGP SIGNATURE-----
Merge tag 'v1.24.0rc2' into develop
Synapse 1.24.0rc2 (2020-12-04)
==============================
Bugfixes
--------
- Fix a regression in v1.24.0rc1 which failed to allow SAML mapping providers which were unable to redirect users to an additional page. ([\#8878](https://github.com/matrix-org/synapse/issues/8878))
Internal Changes
----------------
- Add support for the `prometheus_client` newer than 0.9.0. Contributed by Jordan Bancino. ([\#8875](https://github.com/matrix-org/synapse/issues/8875))
Replaces the `federation_ip_range_blacklist` configuration setting with an
`ip_range_blacklist` setting with wider scope. It now applies to:
* Federation
* Identity servers
* Push notifications
* Checking key validitity for third-party invite events
The old `federation_ip_range_blacklist` setting is still honored if present, but
with reduced scope (it only applies to federation and identity servers).
This was broken in #8801 when abstracting code shared with OIDC.
After this change both SAML and OIDC have a concept of
grandfathering users, but with different implementations.
The spec requires synapse to support `identifier` dicts for `m.login.password`
user-interactive auth, which it did not (instead, it required an undocumented
`user` parameter.)
To fix this properly, we need to pull the code that interprets `identifier`
into `AuthHandler.validate_login` so that it can be called from the UIA code.
Fixes#5665.
Checks that the localpart returned by mapping providers for SAML and
OIDC are valid before registering new users.
Extends the OIDC tests for existing users and invalid data.
* Consistently use room_id from federation request body
Some federation APIs have a redundant `room_id` path param (see
https://github.com/matrix-org/matrix-doc/issues/2330). We should make sure we
consistently use either the path param or the body param, and the body param is
easier.
* Kill off some references to "context"
Once upon a time, "rooms" were known as "contexts". I think this kills of the
last references to "contexts".
We do it this way round so that only the "owner" can delete the access token (i.e. `/logout/all` by the "owner" also deletes that token, but `/logout/all` by the "target user" doesn't).
A future PR will add an API for creating such a token.
When the target user and authenticated entity are different the `Processed request` log line will be logged with a: `{@admin:server as @bob:server} ...`. I'm not convinced by that format (especially since it adds spaces in there, making it harder to use `cut -d ' '` to chop off the start of log lines). Suggestions welcome.
#8567 started a span for every background process. This is good as it means all Synapse code that gets run should be in a span (unless in the sentinel logging context), but it means we generate about 15x the number of spans as we did previously.
This PR attempts to reduce that number by a) not starting one for send commands to Redis, and b) deferring starting background processes until after we're sure they're necessary.
I don't really know how much this will help.
* Fix outbound federaion with multiple event persisters.
We incorrectly notified federation senders that the minimum persisted
stream position had advanced when we got an `RDATA` from an event
persister.
Notifying of federation senders already correctly happens in the
notifier, so we just delete the offending line.
* Change some interfaces to use RoomStreamToken.
By enforcing use of `RoomStreamTokens` we make it less likely that
people pass in random ints that they got from somewhere random.
Co-authored-by: Benjamin Koch <bbbsnowball@gmail.com>
This adds configuration flags that will match a user to pre-existing users
when logging in via OpenID Connect. This is useful when switching to
an existing SSO system.
* Create a new function to verify that the length of a device name is
under a certain threshold.
* Refactor old code and tests to use said function.
* Verify device name length during registration of device
* Add a test for the above
Signed-off-by: Dionysis Grigoropoulos <dgrig@erethon.com>
`pusher_pool.on_new_notifications` expected a min and max stream ID, however that was not what we were passing in. Instead, let's just pass it the current max stream ID and have it track the last stream ID it got passed.
I believe that it mostly worked as we called the function for every event. However, it would break for events that got persisted out of order, i.e, that were persisted but the max stream ID wasn't incremented as not all preceding events had finished persisting, and push for that event would be delayed until another event got pushed to the effected users.
Fixes https://github.com/matrix-org/synapse/issues/8238
Alongside the delta file, some changes were also necessary to the codebase to remove references to the now defunct `populate_stats_process_rooms_2` background job. Thankfully the latter doesn't seem to have made it into any documentation yet :)
`StatsHandler` handles updates to the `current_state_delta_stream`, and updates room stats such as the amount of state events, joined users, etc.
However, it counts every new join membership as a new user entering a room (and that user being in another room), whereas it's possible for a user's membership status to go from join -> join, for instance when they change their per-room profile information.
This PR adds a check for join->join membership transitions, and bails out early, as none of the further checks are necessary at that point.
Due to this bug, membership stats in many rooms have ended up being wildly larger than their true values. I am not sure if we also want to include a migration step which recalculates these statistics (possibly using the `_populate_stats_process_rooms` bg update).
Bug introduced in the initial implementation https://github.com/matrix-org/synapse/pull/4338.
The CI appears to use the latest version of isort, which is a problem when isort gets a major version bump. Rather than try to pin the version, I've done the necessary to make isort5 happy with synapse.
Fixes https://github.com/matrix-org/synapse/issues/2431
Adds config option `encryption_enabled_by_default_for_room_type`, which determines whether encryption should be enabled with the default encryption algorithm in private or public rooms upon creation. Whether the room is private or public is decided based upon the room creation preset that is used.
Part of this PR is also pulling out all of the individual instances of `m.megolm.v1.aes-sha2` into a constant variable to eliminate typos ala https://github.com/matrix-org/synapse/pull/7637
Based on #7637
While working on https://github.com/matrix-org/synapse/issues/5665 I found myself digging into the `Ratelimiter` class and seeing that it was both:
* Rather undocumented, and
* causing a *lot* of config checks
This PR attempts to refactor and comment the `Ratelimiter` class, as well as encourage config file accesses to only be done at instantiation.
Best to be reviewed commit-by-commit.
The idea here is that if an instance persists an event via the replication HTTP API it can return before we receive that event over replication, which can lead to races where code assumes that persisting an event immediately updates various caches (e.g. current state of the room).
Most of Synapse doesn't hit such races, so we don't do the waiting automagically, instead we do so where necessary to avoid unnecessary delays. We may decide to change our minds here if it turns out there are a lot of subtle races going on.
People probably want to look at this commit by commit.
