From 273d7e0dd25d2d6a564259f54c42a54ea282db42 Mon Sep 17 00:00:00 2001
From: M66B <M66B@users.noreply.github.com>
Date: Sun, 18 Jul 2021 13:38:13 +0200
Subject: [PATCH] BIMI: check DMARC policy

---
 app/src/main/java/eu/faircode/email/Bimi.java | 37 ++++++++++++-------
 .../java/eu/faircode/email/MessageHelper.java | 16 ++++++++
 2 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/app/src/main/java/eu/faircode/email/Bimi.java b/app/src/main/java/eu/faircode/email/Bimi.java
index 22397b53ce..41c98c6334 100644
--- a/app/src/main/java/eu/faircode/email/Bimi.java
+++ b/app/src/main/java/eu/faircode/email/Bimi.java
@@ -53,11 +53,12 @@ import java.security.cert.TrustAnchor;
 import java.security.cert.X509CertSelector;
 import java.security.cert.X509Certificate;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.Enumeration;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 
@@ -72,6 +73,10 @@ public class Bimi {
     private static final int READ_TIMEOUT = 15 * 1000; // milliseconds
     private static final String OID_BrandIndicatorforMessageIdentification = "1.3.6.1.5.5.7.3.31";
 
+    private static final List<String> DMARC_POLICIES = Collections.unmodifiableList(Arrays.asList(
+            "quarantine", "reject"
+    ));
+
     static Pair<Bitmap, Boolean> get(
             Context context, String domain, String selector, int scaleToPixels)
             throws IOException {
@@ -85,27 +90,18 @@ public class Bimi {
         DnsHelper.DnsRecord[] records;
         try {
             String txt = selector + "._bimi." + domain;
-            Log.i("BIMI fetch TXT=" + txt);
+            Log.i("BIMI fetch TXT " + txt);
             records = DnsHelper.lookup(context, txt, "txt");
             if (records.length == 0)
                 return null;
-            Log.i("BIMI got TXT=" + records[0].name);
+            Log.i("BIMI got TXT " + records[0].name);
         } catch (Throwable ex) {
             Log.i(ex);
             return null;
         }
 
-        // Decode DNS record
-        Map<String, String> values = new HashMap<>();
-        String[] params = records[0].name.split(";");
-        for (String param : params) {
-            String[] kv = param.split("=");
-            if (kv.length != 2)
-                continue;
-            values.put(kv[0].trim().toLowerCase(), kv[1].trim());
-        }
-
         // Process DNS record
+        Map<String, String> values = MessageHelper.getKeyValues(records[0].name);
         List<String> tags = new ArrayList<>(values.keySet());
         Collections.sort(tags); // process certificate first
         for (String tag : tags) {
@@ -297,6 +293,21 @@ public class Bimi {
                         cpv.validate(path.getCertPath(), pparams);
 
                         Log.i("BIMI valid domain=" + domain);
+
+                        // Get DMARC record
+                        String txt = "_dmarc." + domain;
+                        Log.i("BIMI fetch TXT " + txt);
+                        records = DnsHelper.lookup(context, txt, "txt");
+                        if (records.length == 0)
+                            throw new IllegalArgumentException("DMARC missing");
+                        Log.i("BIMI got TXT " + records[0].name);
+
+                        Map<String, String> dmarc = MessageHelper.getKeyValues(records[0].name);
+                        String policy = dmarc.get("p");
+                        if (policy == null ||
+                                !DMARC_POLICIES.contains(policy.toLowerCase(Locale.ROOT)))
+                            throw new IllegalArgumentException("DMARC invalid policy=" + policy);
+
                         verified = true;
                     } catch (MalformedURLException ex) {
                         Log.i(ex);
diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index 725b5ee02f..0afed26861 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -3001,4 +3001,20 @@ public class MessageHelper {
 
         return true;
     }
+
+    static Map<String, String> getKeyValues(String value) {
+        Map<String, String> values = new HashMap<>();
+        if (TextUtils.isEmpty(value))
+            return values;
+
+        String[] params = value.split(";");
+        for (String param : params) {
+            String[] kv = param.split("=");
+            if (kv.length != 2)
+                continue;
+            values.put(kv[0].trim().toLowerCase(), kv[1].trim());
+        }
+
+        return values;
+    }
 }