From 92fbdcb947d7305cb9d4d962f39b15278cbcef3a Mon Sep 17 00:00:00 2001
From: Andrew Ayer <andrew@sslmate.com>
Date: Tue, 10 May 2016 10:37:10 -0700
Subject: [PATCH] Support crazy wildcards (not just in the left-most label)

---
 cmd/certspotter/main.go | 69 +++++++++++++++++++++--------------------
 helpers.go              | 18 +++++++++++
 2 files changed, 53 insertions(+), 34 deletions(-)

diff --git a/cmd/certspotter/main.go b/cmd/certspotter/main.go
index 354b2e7..4055d0f 100644
--- a/cmd/certspotter/main.go
+++ b/cmd/certspotter/main.go
@@ -40,19 +40,12 @@ func trimTrailingDots (value string) string {
 }
 
 var stateDir = flag.String("state_dir", DefaultStateDir(), "Directory for storing state")
-var watchDomains []string
-var watchDomainSuffixes []string
-
-func addWatchDomain (asciiDomain string) {
-	watchDomains = append(watchDomains, asciiDomain)
-	watchDomainSuffixes = append(watchDomainSuffixes, "." + asciiDomain)
-}
+var watchDomains [][]string
 
 func setWatchDomains (domains []string) error {
 	for _, domain := range domains {
 		if domain == "." { // "." as in root zone (matches everything)
-			watchDomains = []string{}
-			watchDomainSuffixes = []string{""}
+			watchDomains = [][]string{[]string{}}
 			break
 		} else {
 			asciiDomain, err := idna.ToASCII(strings.ToLower(trimTrailingDots(domain)))
@@ -60,44 +53,52 @@ func setWatchDomains (domains []string) error {
 				return fmt.Errorf("Invalid domain `%s': %s", domain, err)
 			}
 
-			addWatchDomain(asciiDomain)
-
-			// Also monitor DNS names that _might_ match this domain (wildcards,
-			// label redactions, and unparseable labels).
-			// For example, if we're monitoring sub.example.com, also monitor:
-			//   *.example.com
-			//   ?.example.com
-			//   <unparsable>.example.com
-			// TODO: support for wildcards that are not the entire label (e.g. ac-*.fr)
-			var parentDomain string
-			if dot := strings.IndexRune(asciiDomain, '.'); dot != -1 {
-				parentDomain = asciiDomain[dot:]
-			}
-			addWatchDomain("*" + parentDomain)
-			addWatchDomain("?" + parentDomain)
-			addWatchDomain(certspotter.UnparsableDNSLabelPlaceholder + parentDomain)
+			watchDomains = append(watchDomains, strings.Split(asciiDomain, "."))
 		}
 	}
 	return nil
 }
 
-func dnsNameMatches (dnsName string) bool {
-	for _, domain := range watchDomains {
-		if dnsName == domain {
-			return true
+func dnsLabelMatches (certLabel string, watchLabel string) bool {
+	// For fail-safe behavior, if a label was unparsable, it matches everything.
+	// Similarly, redacted labels match everything, since the label _might_ be
+	// for a name we're interested in.
+
+	return certLabel == "*" ||
+	       certLabel == "?" ||
+	       certLabel == certspotter.UnparsableDNSLabelPlaceholder ||
+	       certspotter.MatchWildcard(certLabel, watchLabel)
+}
+
+func dnsNameMatches (dnsName []string, watchDomain []string) bool {
+	for len(dnsName) > 0 && len(watchDomain) > 0 {
+		certLabel := dnsName[len(dnsName)-1]
+		watchLabel := watchDomain[len(watchDomain)-1]
+
+		if !dnsLabelMatches(certLabel, watchLabel) {
+			return false
 		}
+
+		dnsName = dnsName[:len(dnsName)-1]
+		watchDomain = watchDomain[:len(watchDomain)-1]
 	}
-	for _, domainSuffix := range watchDomainSuffixes {
-		if strings.HasSuffix(dnsName, domainSuffix) {
+
+	return len(watchDomain) == 0
+}
+
+func dnsNameIsWatched (dnsName string) bool {
+	labels := strings.Split(dnsName, ".")
+	for _, watchDomain := range watchDomains {
+		if dnsNameMatches(labels, watchDomain) {
 			return true
 		}
 	}
 	return false
 }
 
-func anyDnsNameMatches (dnsNames []string) bool {
+func anyDnsNameIsWatched (dnsNames []string) bool {
 	for _, dnsName := range dnsNames {
-		if dnsNameMatches(dnsName) {
+		if dnsNameIsWatched(dnsName) {
 			return true
 		}
 	}
@@ -122,7 +123,7 @@ func processEntry (scanner *certspotter.Scanner, entry *ct.LogEntry) {
 	// parse error), report the certificate because we can't say for sure it
 	// doesn't match a domain we care about.  We try very hard to make sure
 	// parsing identifiers always succeeds, so false alarms should be rare.
-	if info.Identifiers == nil || anyDnsNameMatches(info.Identifiers.DNSNames) {
+	if info.Identifiers == nil || anyDnsNameIsWatched(info.Identifiers.DNSNames) {
 		cmd.LogEntry(&info)
 	}
 }
diff --git a/helpers.go b/helpers.go
index 30bec3f..964018b 100644
--- a/helpers.go
+++ b/helpers.go
@@ -399,3 +399,21 @@ func WriteCertRepository (repoPath string, isPrecert bool, certs [][]byte) (bool
 
 	return false, path, nil
 }
+
+func MatchWildcard (pattern string, dnsName string) bool {
+	for len(pattern) > 0 {
+		if pattern[0] == '*' {
+			if len(dnsName) > 0 && dnsName[0] != '.' && MatchWildcard(pattern, dnsName[1:]) {
+				return true
+			}
+			pattern = pattern[1:]
+		} else {
+			if len(dnsName) == 0 || pattern[0] != dnsName[0] {
+				return false
+			}
+			pattern = pattern[1:]
+			dnsName = dnsName[1:]
+		}
+	}
+	return len(dnsName) == 0
+}