From 109d38e1b1e390637412f5fe1f051167d8329a37 Mon Sep 17 00:00:00 2001
From: genofire <geno+dev@fireorbit.de>
Date: Mon, 10 Feb 2020 00:57:58 +0100
Subject: [PATCH] [BUGFIX] Resolver: fallback for invalid SRV CNAME entries

---
 .../siacs/conversations/utils/Resolver.java   | 40 ++++++++++++++++++-
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/main/java/eu/siacs/conversations/utils/Resolver.java b/src/main/java/eu/siacs/conversations/utils/Resolver.java
index d35a7ae2f..2c71afe4c 100644
--- a/src/main/java/eu/siacs/conversations/utils/Resolver.java
+++ b/src/main/java/eu/siacs/conversations/utils/Resolver.java
@@ -172,6 +172,9 @@ public class Resolver {
         ResolverResult<SRV> result = resolveWithFallback(dnsName, SRV.class);
         final List<Result> results = new ArrayList<>();
         final List<Thread> threads = new ArrayList<>();
+
+        final List<Result> fallbackResults = new ArrayList<>();
+        final List<Thread> fallbackThreads = new ArrayList<>();
         for (SRV record : result.getAnswersOrEmptySet()) {
             if (record.name.length() == 0) {
                 continue;
@@ -188,6 +191,22 @@ public class Resolver {
                     results.addAll(ipv4s);
                 }
             }));
+            fallbackThreads.add(new Thread(() -> {
+                try {
+                    for (CNAME cname : resolveWithFallback(record.name, CNAME.class, result.isAuthenticData()).getAnswersOrEmptySet()) {
+                        final List<Result> ipv6s = resolveIp(record, cname.name, AAAA.class, result.isAuthenticData(), directTls);
+                        synchronized (fallbackResults) {
+                            fallbackResults.addAll(ipv6s);
+                        }
+                        final List<Result> ipv4s = resolveIp(record, cname.name, A.class, result.isAuthenticData(), directTls);
+                        synchronized (results) {
+                            fallbackResults.addAll(ipv4s);
+                        }
+                    }
+                } catch (Throwable throwable) {
+                    Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + "error resolving srv cname-fallback records", throwable);
+                }
+            }));
         }
         for (Thread thread : threads) {
             thread.start();
@@ -199,13 +218,30 @@ public class Resolver {
                 return Collections.emptyList();
             }
         }
-        return results;
+        if (results.size() > 0) {
+            return results;
+        }
+
+        for (Thread thread : fallbackThreads) {
+            thread.start();
+        }
+        for (Thread thread : fallbackThreads) {
+            try {
+                thread.join();
+            } catch (InterruptedException e) {
+                return Collections.emptyList();
+            }
+        }
+        return fallbackResults;
     }
 
     private static <D extends InternetAddressRR> List<Result> resolveIp(SRV srv, Class<D> type, boolean authenticated, boolean directTls) {
+        return resolveIp(srv, srv.name, type, authenticated, directTls);
+    }
+    private static <D extends InternetAddressRR> List<Result> resolveIp(SRV srv, DNSName hostname, Class<D> type, boolean authenticated, boolean directTls) {
         List<Result> list = new ArrayList<>();
         try {
-            ResolverResult<D> results = resolveWithFallback(srv.name, type, authenticated);
+            ResolverResult<D> results = resolveWithFallback(hostname, type, authenticated);
             for (D record : results.getAnswersOrEmptySet()) {
                 Result resolverResult = Result.fromRecord(srv, directTls);
                 resolverResult.authenticated = results.isAuthenticData() && authenticated;