add PTR/rDNS match check and ASN/org lookup via WHOIS

- DNS: reverse DNS lookup on A record IPs to verify PTR configuration

- Infra: ASN and organization lookup via whois.radb.net

- Refactor checkARecords to return resolved IPs for downstream use

Signed-off-by: Blake Ridgway <blake@blakeridgway.com>

internal/dns/checker.go

@@ -12,8 +12,9 @@ import (
 func Run(domain string) types.DNSResult {
 	var checks []types.CheckResult
 
-	// A records
-	checks = append(checks, checkARecords(domain)...)
+	// A records (also resolves IPs for PTR check)
+	ips, aRecordChecks := checkARecords(domain)
+	checks = append(checks, aRecordChecks...)
 
 	// AAAA records
 	checks = append(checks, checkAAAARecords(domain)...)
@@ -27,13 +28,17 @@ func Run(domain string) types.DNSResult {
 	// DNSSEC
 	checks = append(checks, checkDNSSEC(domain)...)
 
+	// PTR / rDNS match
+	checks = append(checks, checkPTR(ips)...)
+
 	return types.DNSResult{Checks: checks}
 }
 
-func checkARecords(domain string) []types.CheckResult {
+// checkARecords returns the resolved IPv4 addresses and the check results.
+func checkARecords(domain string) ([]string, []types.CheckResult) {
 	ips, err := net.LookupHost(domain)
 	if err != nil {
-		return []types.CheckResult{{Status: types.StatusFail, Message: fmt.Sprintf("no A record: %v", err)}}
+		return nil, []types.CheckResult{{Status: types.StatusFail, Message: fmt.Sprintf("no A record: %v", err)}}
 	}
 	var ipv4 []string
 	for _, ip := range ips {
@@ -42,9 +47,9 @@ func checkARecords(domain string) []types.CheckResult {
 		}
 	}
 	if len(ipv4) == 0 {
-		return []types.CheckResult{{Status: types.StatusFail, Message: "no A record found"}}
+		return nil, []types.CheckResult{{Status: types.StatusFail, Message: "no A record found"}}
 	}
-	return []types.CheckResult{{Status: types.StatusOK, Message: fmt.Sprintf("A record: %s", strings.Join(ipv4, ", "))}}
+	return ipv4, []types.CheckResult{{Status: types.StatusOK, Message: fmt.Sprintf("A record: %s", strings.Join(ipv4, ", "))}}
 }
 
 func checkAAAARecords(domain string) []types.CheckResult {
@@ -59,7 +64,7 @@ func checkAAAARecords(domain string) []types.CheckResult {
 		}
 	}
 	if len(ipv6) == 0 {
-		return nil // Not a warning; many sites don't have IPv6
+		return nil
 	}
 	return []types.CheckResult{{Status: types.StatusOK, Message: fmt.Sprintf("AAAA record: %s", strings.Join(ipv6, ", "))}}
 }
@@ -82,7 +87,6 @@ func checkTXTRecords(domain string) []types.CheckResult {
 
 	var checks []types.CheckResult
 	hasSPF := false
-	hasDMARC := false
 
 	for _, txt := range txts {
 		if strings.HasPrefix(txt, "v=spf1") {
@@ -109,16 +113,12 @@ func checkTXTRecords(domain string) []types.CheckResult {
 	if err == nil {
 		for _, txt := range dmarcTxts {
 			if strings.HasPrefix(txt, "v=DMARC1") {
-				hasDMARC = true
-				break
+				checks = append(checks, types.CheckResult{Status: types.StatusOK, Message: "DMARC record found"})
+				return checks
 			}
 		}
 	}
-	if hasDMARC {
-		checks = append(checks, types.CheckResult{Status: types.StatusOK, Message: "DMARC record found"})
-	} else {
-		checks = append(checks, types.CheckResult{Status: types.StatusWarn, Message: "no DMARC record"})
-	}
+	checks = append(checks, types.CheckResult{Status: types.StatusWarn, Message: "no DMARC record"})
 
 	return checks
 }
@@ -137,19 +137,47 @@ func checkDKIM(domain string) bool {
 }
 
 func checkDNSSEC(domain string) []types.CheckResult {
-	// DNSSEC is checked via looking up the DS record on the parent zone.
-	// For simplicity, we check if the domain has RRSIG records by looking up
-	// the NS records and checking for authenticated data.
-	// A true DNSSEC check requires a validating resolver. We do a best-effort
-	// check by seeing if the resolver returns authenticated data headers.
-	// As a simple heuristic, we check for DNSKEY records.
 	_, err := net.LookupTXT("_dnssec." + domain)
 	if err == nil {
 		return []types.CheckResult{{Status: types.StatusOK, Message: "DNSSEC appears enabled"}}
 	}
-	// Try to retrieve DNSKEY records as a secondary heuristic
-	// Note: Go's net package doesn't expose DNSKEY record types directly.
-	// A full DNSSEC check would require a custom DNS resolver.
 	return []types.CheckResult{{Status: types.StatusInfo, Message: "DNSSEC check requires custom resolver (not verified)"}}
 }
 
+// checkPTR performs a reverse DNS lookup on the given IPs and checks if
+// any returned hostname resolves back to one of the original IPs.
+func checkPTR(ips []string) []types.CheckResult {
+	if len(ips) == 0 {
+		return nil
+	}
+
+	// Check up to the first 2 IPs to keep things fast.
+	limit := 2
+	if len(ips) < limit {
+		limit = len(ips)
+	}
+
+	for i := 0; i < limit; i++ {
+		ip := ips[i]
+		names, err := net.LookupAddr(ip)
+		if err != nil || len(names) == 0 {
+			continue
+		}
+
+		for _, name := range names {
+			name = strings.TrimSuffix(name, ".")
+			resolved, err := net.LookupHost(name)
+			if err != nil {
+				continue
+			}
+			for _, resolvedIP := range resolved {
+				if resolvedIP == ip {
+					return []types.CheckResult{{Status: types.StatusOK, Message: fmt.Sprintf("rDNS matches (%s → %s)", ip, name)}}
+				}
+			}
+		}
+	}
+
+	return []types.CheckResult{{Status: types.StatusInfo, Message: "no PTR record found (rDNS not configured)"}}
+}
+

internal/infra/checker.go

@@ -1,6 +1,7 @@
 package infra
 
 import (
+	"bufio"
 	"fmt"
 	"net"
 	"strings"
@@ -72,6 +73,20 @@ func Run(domain string, resolvedIPs []string) types.InfraResult {
 	}
 	result.CDN = cdn
 
+	// ASN / org lookup via WHOIS
+	asn, org := lookupASN(targetIP)
+	if asn != "" {
+		result.ASN = asn
+		result.Org = org
+		msg := fmt.Sprintf("ASN: %s", asn)
+		if org != "" {
+			msg += fmt.Sprintf(" (%s)", org)
+		}
+		result.Checks = append(result.Checks, types.CheckResult{
+			Status: types.StatusInfo, Message: msg,
+		})
+	}
+
 	// Common ports check
 	result.Checks = append(result.Checks, checkPorts(targetIP)...)
 
@@ -107,6 +122,42 @@ func detectCDN(ip string) string {
 	return ""
 }
 
+// lookupASN queries whois.radb.net for the ASN and organization of an IP.
+func lookupASN(ip string) (asn, org string) {
+	conn, err := net.DialTimeout("tcp", "whois.radb.net:43", 5*time.Second)
+	if err != nil {
+		return "", ""
+	}
+	defer conn.Close()
+
+	// Set a deadline for the entire WHOIS exchange.
+	conn.SetDeadline(time.Now().Add(10 * time.Second))
+
+	fmt.Fprintf(conn, "%s\r\n", ip)
+
+	scanner := bufio.NewScanner(conn)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if asn == "" && strings.HasPrefix(line, "origin:") {
+			asn = strings.TrimSpace(strings.TrimPrefix(line, "origin:"))
+			asn = strings.ToUpper(asn)
+		}
+		if org == "" && strings.HasPrefix(line, "descr:") {
+			org = strings.TrimSpace(strings.TrimPrefix(line, "descr:"))
+		}
+		if asn != "" && org != "" {
+			break
+		}
+	}
+
+	// Trim long descriptions to keep output readable.
+	if len(org) > 80 {
+		org = org[:77] + "..."
+	}
+
+	return asn, org
+}
+
 func checkPorts(ip string) []types.CheckResult {
 	var checks []types.CheckResult
 	var mu sync.Mutex