Prevent federation client server being flooded by NC 16.0 cloud share issue

[hcderaad]

Steps to reproduce

1. Make a federated share from an NC 16.0 server to a federation client (other server) of any other version
2. The logs will be flooded with Doctrine issues regarding problems with queries on the oc_filecache not being prepopulated with the right query parameters
3. Other shares will stop working on the guest/client NC server and it is impossible to delete the federated share.

Expected behaviour

The receiving NC server should not be impacted by a problem of a federated share from another server.

Actual behaviour

The receiving NC server is severely impacted by the problem created by the remote federated share host.

Server configuration

Operating system:
openSUSE Tumbleweed (most recent version)

Web server:
Apache 2.4

Database:
MariaDB latest version

PHP version:
PHP 7.x

Nextcloud version: (see Nextcloud admin page)
16.0.1

Updated from an older Nextcloud/ownCloud or fresh install:
Updated, but irrelevant

Where did you install Nextcloud from:
openSUSE package, yet I have reproduced this problem with tar.gz instances as well.

Signing status:
?

List of activated apps:
NA

Nextcloud configuration:
NA

Are you using external storage, if yes which one: local/smb/sftp/...
Only federated shares

Are you using encryption: yes/no
No

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/...
No

Client configuration

Browser:
Firefox, but also relevant for others as it is a server issue.

Operating system:
NA

Logs

Web server error log

NA

Nextcloud log (data/nextcloud.log)

The relevant error is Doctrine\DBAL\Exception\DriverException: An exception occurred while executing 'UPDATE oc_filecache SET =? WHERE ( <> ? OR IS NULL) AND fileid = ? ' with params ["199247"]: SQLSTATE[HY093]: Invalid parameter number: number of bound variables does not match number of tokens

Browser log

NA

[hcderaad]

The issue was fixed on the side of the federation server by this PR. Yet on the federation client apparently not enough input filtering is applied to prevent malformed JSON (or doubly nested) message bodies to escalate on to a Doctrine error. Will perform some debugging later. #15399

[hcderaad]

Looking at the cache update function, it appears that no input checking/validation is done on the $data attribute. This should be checked before propagating an update:
https://github.com/nextcloud/server/blob/master/lib/private/Files/Cache/Cache.php#L235

[hcderaad]

And also looking at the files external app, there is no input validation being performed on whatever response is given by the remote server.
This would probably be a good place to automatically disable a misbehaving remote server to prevent further propagation of issues on the local/client server.
https://github.com/nextcloud/server/blob/master/apps/files_sharing/lib/External/Scanner.php#L110

[hcderaad]

On second thought, it probably makes more sense to add checking the validity of a server response on individual file level in this method:
https://github.com/nextcloud/server/blob/master/apps/files_sharing/lib/External/Storage.php#L208

As this misbehavior should actually result in a StorageInvalidException or a StorageNotAvailableException

If this method testRemote would also check for at least one valid file response, this issue would probably be mitigated. Ideally, if a server does indeed misbehave, it should raise an Error and is automatically suspended from further syncing until an admin reenables it.
https://github.com/nextcloud/server/blob/master/apps/files_sharing/lib/External/Storage.php#L252

[kesselb]

Does this error still occur?

This issue has been automatically marked as stale because it has not had recent activity and seems to be missing some essential information. It will be closed if no further activity occurs. Thank you for your contributions.