smallwebwaf/internal/waf/biased.go

package waf

import (
	"sneak.berlin/go/smallwebwaf/internal/config"
)

// whole is the percentage of each limit a client gets when no biased
// threshold lowers its limits.
const whole = 100

// percentage is a client's limit percentage for the rate limits or for
// the byte limits, as the biased thresholds give it, and the setting that
// gave it: "" with whole when none lowers that kind of limit.
type percentage struct {
	percent int64
	setting string
}

// biasedThresholdsSet reports whether a biased threshold can lower a
// client's limits by its lookup: SWW_ASN_BYTES_PERCENT or
// SWW_COUNTRY_BYTES_PERCENT is not empty, SWW_UNKNOWN_LIMIT_PERCENT is
// below 100, or SWW_ASN_LIMIT_PERCENT_URL is set. The client's lookup is
// then needed before its request goes on.
func biasedThresholdsSet(cfg *config.Config) bool {
	return len(cfg.ASNBytesPercent) > 0 ||
		len(cfg.CountryBytesPercent) > 0 ||
		cfg.UnknownLimitPercent < whole ||
		cfg.ASNLimitPercentURL != ""
}

// limitPercentages returns the client's limit percentages, for the rate
// limits and for the byte limits, by its tags, its AS number and country
// as looked up, each "" when unknown, and the blocklists, DNSBL zones and
// AbuseIPDB that list it. Each is the lowest of those the settings give
// it, the first of them in the order below when several are lowest: the
// percentage SWW_TAG_LIMIT_PERCENT gives its asn= tag, the one the file
// SWW_ASN_LIMIT_PERCENT_URL names gives its AS number, the one
// SWW_TAG_LIMIT_PERCENT gives its country= tag, the lowest it gives its
// other tags, for a client without a country, unless its request skipped
// the wait for GeoJS, SWW_UNKNOWN_LIMIT_PERCENT, for a client a blocklist
// lists, the percentage of SWW_BLOCKLIST_ACTION while it is limit, and
// for a client a DNSBL zone's verdict lists, or whose AbuseIPDB score is
// a hit, the percentage of SWW_REPUTATION_ACTION while it is limit. For
// the byte limits, SWW_ASN_BYTES_PERCENT and SWW_COUNTRY_BYTES_PERCENT
// take the place of the first three for an AS number or a country they
// list.
func (rq *request) limitPercentages() (percentage, percentage) {
	cfg := rq.h.config
	asn, country := rq.line.ASN, rq.line.Country

	unknown := percentage{percent: whole}
	if country == "" && !rq.skippedLookupWait {
		unknown = percentage{
			cfg.UnknownLimitPercent,
			"SWW_UNKNOWN_LIMIT_PERCENT",
		}
	}

	fetched := percentage{percent: whole}
	if percent, listed := rq.h.lists.ASNLimitPercent(asn); listed {
		fetched = percentage{percent, "SWW_ASN_LIMIT_PERCENT_URL"}
	}

	blocklisted := percentage{percent: whole}
	if rq.blocklisted && cfg.BlocklistAction == "limit" {
		blocklisted = percentage{
			cfg.BlocklistLimitPercent,
			"SWW_BLOCKLIST_ACTION",
		}
	}

	reputationListed := percentage{percent: whole}
	if (rq.dnsblListed || rq.abuseIPDBHit) &&
		cfg.ReputationAction == "limit" {
		reputationListed = percentage{
			cfg.ReputationLimitPercent,
			"SWW_REPUTATION_ACTION",
		}
	}

	const tagSetting = "SWW_TAG_LIMIT_PERCENT"

	asnRequests := lowest(
		given(cfg.TagLimitPercent, asnTag(asn), tagSetting),
		fetched,
	)
	countryRequests := given(
		cfg.TagLimitPercent,
		countryTag(country),
		tagSetting,
	)

	otherTags := percentage{percent: whole}

	for _, tag := range rq.line.Tags {
		if tag != asnTag(asn) && tag != countryTag(country) {
			otherTags = lowest(
				otherTags,
				given(cfg.TagLimitPercent, tag, tagSetting),
			)
		}
	}

	asnBytes, countryBytes := asnRequests, countryRequests
	if _, listed := cfg.ASNBytesPercent[asn]; listed {
		asnBytes = given(cfg.ASNBytesPercent, asn, "SWW_ASN_BYTES_PERCENT")
	}

	if _, listed := cfg.CountryBytesPercent[country]; listed {
		countryBytes = given(
			cfg.CountryBytesPercent,
			country,
			"SWW_COUNTRY_BYTES_PERCENT",
		)
	}

	// The limits that lower requests and bytes alike.
	common := lowest(otherTags, unknown, blocklisted, reputationListed)

	return lowest(asnRequests, countryRequests, common),
		lowest(asnBytes, countryBytes, common)
}

// given returns the percentage percents, the setting named setting, gives
// code, an AS number, a country or a tag, or whole when it does not list code.
func given(percents map[string]int64, code, setting string) percentage {
	percent, listed := percents[code]
	if !listed {
		return percentage{percent: whole}
	}

	return percentage{percent, setting}
}

// lowest returns the lowest of percentages below whole, the first of them
// when several are lowest, or whole when none is below it.
func lowest(percentages ...percentage) percentage {
	low := percentage{percent: whole}

	for _, p := range percentages {
		if p.percent < low.percent {
			low = p
		}
	}

	return low
}

// logged returns p as the log line and the notes of a ban give it: its
// percent and setting, or nil and "" for whole, which they leave out.
func (p percentage) logged() (*int64, string) {
	if p.percent == whole {
		return nil, ""
	}

	return &p.percent, p.setting
}