[bugfix] check remote status permissibility (#2703)

* add more stringent checks for remote status permissibility

* add check for inreplyto of a remote status being a boost

* do not permit inReplyTo boost wrapper statuses

* change comment wording

* fix calls to NewFederator()

* add code comments for NotPermitted() and SetNotPermitted()

* improve comment

* check that existing != nil before attempting delete

* ensure replying account isn't suspended

* use a debug log instead of info. check for boost using ID

* shorten log string length. make info level

* add note that replying to boost wrapper status shouldn't be able to happen anyways

* update to use onFail() function

internal/federation/dereferencing/status.go

@@ -503,9 +503,16 @@ func (d *Dereferencer) enrichStatus(
 	latestStatus.FetchedAt = time.Now()
 	latestStatus.Local = status.Local
 
-	// Ensure the status' poll remains consistent, else reset the poll.
-	if err := d.fetchStatusPoll(ctx, status, latestStatus); err != nil {
-		return nil, nil, gtserror.Newf("error populating poll for status %s: %w", uri, err)
+	// Check if this is a permitted status we should accept.
+	permit, err := d.isPermittedStatus(ctx, status, latestStatus)
+	if err != nil {
+		return nil, nil, gtserror.Newf("error checking permissibility for status %s: %w", uri, err)
+	}
+
+	if !permit {
+		// Return a checkable error type that can be ignored.
+		err := gtserror.Newf("dropping unpermitted status: %s", uri)
+		return nil, nil, gtserror.SetNotPermitted(err)
 	}
 
 	// Ensure the status' mentions are populated, and pass in existing to check for changes.
@@ -513,6 +520,11 @@ func (d *Dereferencer) enrichStatus(
 		return nil, nil, gtserror.Newf("error populating mentions for status %s: %w", uri, err)
 	}
 
+	// Ensure the status' poll remains consistent, else reset the poll.
+	if err := d.fetchStatusPoll(ctx, status, latestStatus); err != nil {
+		return nil, nil, gtserror.Newf("error populating poll for status %s: %w", uri, err)
+	}
+
 	// Now that we know who this status replies to (handled by ASStatusToStatus)
 	// and who it mentions, we can add a ThreadID to it if necessary.
 	if err := d.threadStatus(ctx, latestStatus); err != nil {
@@ -550,6 +562,84 @@ func (d *Dereferencer) enrichStatus(
 	return latestStatus, apubStatus, nil
 }
 
+// isPermittedStatus returns whether the given status
+// is permitted to be stored on this instance, checking
+// whether the author is suspended, and passes visibility
+// checks against status being replied-to (if any).
+func (d *Dereferencer) isPermittedStatus(
+	ctx context.Context,
+	existing *gtsmodel.Status,
+	status *gtsmodel.Status,
+) (
+	permitted bool, // is permitted?
+	err error,
+) {
+
+	// our failure condition handling
+	// at the end of this function for
+	// the case of permission = false.
+	onFail := func() (bool, error) {
+		if existing != nil {
+			log.Infof(ctx, "deleting unpermitted: %s", existing.URI)
+
+			// Delete existing status from database as it's no longer permitted.
+			if err := d.state.DB.DeleteStatusByID(ctx, existing.ID); err != nil {
+				log.Errorf(ctx, "error deleting %s after permissivity fail: %v", existing.URI, err)
+			}
+		}
+		return false, nil
+	}
+
+	if !status.Account.SuspendedAt.IsZero() {
+		// The status author is suspended,
+		// this shouldn't have reached here
+		// but it's a fast check anyways.
+		return onFail()
+	}
+
+	if status.InReplyToURI == "" {
+		// This status isn't in
+		// reply to anything!
+		return true, nil
+	}
+
+	if status.InReplyTo == nil {
+		// If no inReplyTo has been set,
+		// we return here for now as we
+		// can't perform further checks.
+		//
+		// Worst case we allow something
+		// through, and later on during
+		// refetch it will get deleted.
+		return true, nil
+	}
+
+	if status.InReplyTo.BoostOfID != "" {
+		// We do not permit replies to
+		// boost wrapper statuses. (this
+		// shouldn't be able to happen).
+		return onFail()
+	}
+
+	// Check visibility of inReplyTo to status author.
+	permitted, err = d.visibility.StatusVisible(ctx,
+		status.Account,
+		status.InReplyTo,
+	)
+	if err != nil {
+		return false, gtserror.Newf("error checking in-reply-to visibility: %w", err)
+	}
+
+	if permitted &&
+		*status.InReplyTo.Replyable {
+		// This status is visible AND
+		// replyable, in this economy?!
+		return true, nil
+	}
+
+	return onFail()
+}
+
 // populateMentionTarget tries to populate the given
 // mention with the correct TargetAccount and (if not
 // yet set) TargetAccountURI, returning the populated