Files cannot be saved if in a group folder owned by a different user

[nikkilocke]

I have the group_folders app (and file_versions) in my Nextcloud.

User A is a member of group G, which has a group folder.
User A shares a subdirectory of the group folder with group H (read-write).
User B is a member of group H, so can see the share,
User B opens a docx file in the shared folder, edits it, and attempts to save it.
The save fails.

I have spent a couple of days tracking down the issue. It appears to be in callbackcontroller.php function track.

Extract from code:

        $user = $this->userManager->get($userId);
        if (!empty($user)) {
            \OC_User::setUserId($userId);
        } else {
            if (empty($shareToken)) {
                $this->logger->error("Track without token: $fileId status $status", ["app" => $this->appName]);
                return new JSONResponse(["message" => $this->trans->t("Access denied")], Http::STATUS_FORBIDDEN);
            }

            $this->logger->debug("Track $fileId by token for $userId", ["app" => $this->appName]);
        }

Later on:

        // owner of file from the callback link
        $ownerId = $hashData->ownerId;
        $owner = $this->userManager->get($ownerId);

        if (!empty($owner)) {
            $userId = $ownerId;
        } else {
            $callbackUser = $this->userManager->get($callbackUserId);

            if (!empty($callbackUser)) {
                // author of the callback link
                $userId = $callbackUserId;

                // path for author of the callback link
                $filePath = $hashData->filePath;
            }
        }

        if (!empty($userId)) {
            \OC_Util::setupFS($userId);
        }

Unfortunately, group folder mount points seem to be created for the user set in \OC_User::setUserId($userId); rather than the one passed to \OC_Util::setupFS($userId);.

Moving the call to \OC_User::setUserId($userId); to just before the one to \OC_Util::setupFS($userId); enables the file to be saved (but I guess might have unintended consequences if file modofications are logged to the user?).

Presumably passing the user's id instead of the owner's to setupFS would also work - is there a good reason why you set up the file system as the owner rather than the user?

[nikkilocke]

An alternative fix is not to use the owner id at all.
Not sure why you do that anyway.

[LinneyS]

#660