Fix use-after-free in DNS64 discovery threadt13.0

DNS64 discovery thread is detached from binder requesting thread. But
the discovery thread references resources not belongs to itself, which
can be destroyed in dnsresolver destruction.

Holds a strong pointer of Dns64Configuration in DNS64 discovery thread
so that the instance of Dns64Configuration will keep until the DNS64
thread is force terminated.

Ignore-AOSP-First: Fix security vulnerability
Bug: 278303745
Test: m, fuzzing
Fuzzing: mma resolv_service_fuzzer && adb sync data && adb shell /data/fuzz/arm64/resolv_service_fuzzer/resolv_service_fuzzer

(cherry picked from commit 254115584ff558fb87ee6ec5f5bb043f76219910)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:79f571069c4db536e7c1bfecbb50c926f0ef0548)
Merged-In: Id74ea4e6f54a00805d3cc8a9d7e15e58a473b7d3
Change-Id: Id74ea4e6f54a00805d3cc8a9d7e15e58a473b7d3

1 files changed, 10 insertions, 7 deletions

diff --git a/Dns64Configuration.cpp b/Dns64Configuration.cpp
index a1fe8717..6e5ca5bd 100644
--- a/Dns64Configuration.cpp
+++ b/Dns64Configuration.cpp
@@ -24,6 +24,7 @@
 #include <netdutils/DumpWriter.h>
 #include <netdutils/InternetAddresses.h>
 #include <netdutils/ThreadUtil.h>
+#include <utils/StrongPointer.h>
 #include <thread>
 #include <utility>
 
@@ -36,6 +37,7 @@
 
 namespace android {
 
+using android::sp;
 using netdutils::DumpWriter;
 using netdutils::IPAddress;
 using netdutils::IPPrefix;
@@ -61,8 +63,9 @@ void Dns64Configuration::startPrefixDiscovery(unsigned netId) {
     // Emplace a copy of |cfg| in the map.
     mDns64Configs.emplace(std::make_pair(netId, cfg));
 
+    const sp<Dns64Configuration> thiz = this;
     // Note that capturing |cfg| in this lambda creates a copy.
-    std::thread discovery_thread([this, cfg, netId] {
+    std::thread discovery_thread([thiz, cfg, netId] {
         setThreadName(fmt::format("Nat64Pfx_{}", netId));
 
         // Make a mutable copy rather than mark the whole lambda mutable.
@@ -75,28 +78,28 @@ void Dns64Configuration::startPrefixDiscovery(unsigned netId) {
                                .build();
 
         while (true) {
-            if (!this->shouldContinueDiscovery(evalCfg)) break;
+            if (!thiz->shouldContinueDiscovery(evalCfg)) break;
 
             android_net_context netcontext{};
-            mGetNetworkContextCallback(evalCfg.netId, 0, &netcontext);
+            thiz->mGetNetworkContextCallback(evalCfg.netId, 0, &netcontext);
 
             // Prefix discovery must bypass private DNS because in strict mode
             // the server generally won't know the NAT64 prefix.
             netcontext.flags |= NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
             if (doRfc7050PrefixDiscovery(netcontext, &evalCfg)) {
-                this->recordDns64Config(evalCfg);
+                thiz->recordDns64Config(evalCfg);
                 break;
             }
 
-            if (!this->shouldContinueDiscovery(evalCfg)) break;
+            if (!thiz->shouldContinueDiscovery(evalCfg)) break;
 
             if (!backoff.hasNextTimeout()) break;
             {
-                std::unique_lock<std::mutex> cvGuard(mMutex);
+                std::unique_lock<std::mutex> cvGuard(thiz->mMutex);
                 // TODO: Consider some chrono math, combined with wait_until()
                 // perhaps, to prevent early re-resolves from the removal of
                 // other netids with IPv6-only nameservers.
-                mCv.wait_for(cvGuard, backoff.getNextTimeout());
+                thiz->mCv.wait_for(cvGuard, backoff.getNextTimeout());
             }
         }
     });