From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Lin Lee <linlee@google.com>
Date: Mon, 7 Aug 2023 09:34:41 +0000
Subject: [PATCH] Fix Heap-use-after-free in MDnsSdListener::Monitor::run

Use thread join to avoid thread exiting after instance
recycled.

Prior to implementing this patch, fuzzing would lead to a segmentation fault after approximately 500 rounds. With the addition of the patch, the fuzzing process can now be repeated for over 30,000 rounds.

Test: m, fuzzing
Fuzzing: mma mdns_service_fuzzer && adb sync data && adb shell /data/fuzz/arm64/mdns_service_fuzzer/mdns_service_fuzzer

Bug: 272382770
Ignore-AOSP-First: Security Issue
(cherry picked from commit 9c0c15f80cffb98b36284dd169a2e62e059dbbe3)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:75e5e2e1faec7aa2812fc6fba30d6fe80558bacd)
Merged-In: I5bc85451b4e6539bad45ceb672924a37952cc138
Change-Id: I5bc85451b4e6539bad45ceb672924a37952cc138
---
 server/MDnsSdListener.cpp | 36 ++++++++++++++++++++++++------------
 server/MDnsSdListener.h   |  4 +++-
 2 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/server/MDnsSdListener.cpp b/server/MDnsSdListener.cpp
index ef53d249..6eaaf5c0 100644
--- a/server/MDnsSdListener.cpp
+++ b/server/MDnsSdListener.cpp
@@ -27,6 +27,7 @@
 #include <sys/types.h>
 #include <string.h>
 #include <resolv.h>
+#include <thread>
 
 #define LOG_TAG "MDnsDS"
 #define DBG 1
@@ -524,10 +525,17 @@ MDnsSdListener::Monitor::Monitor() {
     socketpair(AF_LOCAL, SOCK_STREAM, 0, mCtrlSocketPair);
     pthread_mutex_init(&mHeadMutex, NULL);
 
-    const int rval = ::android::net::threadLaunch(this);
-    if (rval != 0) {
-        ALOGW("Error spawning monitor thread: %s (%d)", strerror(-rval), -rval);
-    }
+    mRescanThread = new std::thread(&Monitor::run, this);
+    if (!mRescanThread->joinable()) ALOGE("Unable to launch thread.");
+}
+
+MDnsSdListener::Monitor::~Monitor() {
+    if (VDBG) ALOGD("Monitor recycling");
+    close(mCtrlSocketPair[1]);  // interrupt poll in MDnsSdListener::Monitor::run() and revent will
+                                // be 17 = POLLIN | POLLHUP
+    mRescanThread->join();
+    delete mRescanThread;
+    if (VDBG) ALOGD("Monitor recycled");
 }
 
 #define NAP_TIME 200  // 200 ms between polls
@@ -617,14 +625,18 @@ void MDnsSdListener::Monitor::run() {
                 }
             }
             if (VDBG) ALOGD("controlSocket shows revent= %d", mPollFds[0].revents);
-            switch (mPollFds[0].revents) {
-                case POLLIN: {
-                    char readBuf[2];
-                    read(mCtrlSocketPair[0], &readBuf, 1);
-                    if (DBG) ALOGD("MDnsSdListener::Monitor got %c", readBuf[0]);
-                    if (memcmp(RESCAN, readBuf, 1) == 0) {
-                        pollCount = rescan();
-                    }
+            if (mPollFds[0].revents & POLLHUP) {
+                free(mPollFds);
+                free(mPollRefs);
+                if (VDBG) ALOGD("Monitor thread leaving.");
+                return;
+            }
+            if (mPollFds[0].revents == POLLIN) {
+                char readBuf[2];
+                read(mCtrlSocketPair[0], &readBuf, 1);
+                if (DBG) ALOGD("MDnsSdListener::Monitor got %c", readBuf[0]);
+                if (memcmp(RESCAN, readBuf, 1) == 0) {
+                    pollCount = rescan();
                 }
             }
             mPollFds[0].revents = 0;
diff --git a/server/MDnsSdListener.h b/server/MDnsSdListener.h
index 8c6096e8..2b3cb5e2 100644
--- a/server/MDnsSdListener.h
+++ b/server/MDnsSdListener.h
@@ -20,6 +20,7 @@
 #include <pthread.h>
 #include <sysutils/FrameworkListener.h>
 #include <dns_sd.h>
+#include <thread>
 
 #include "NetdCommand.h"
 
@@ -71,7 +72,7 @@ private:
     class Monitor {
     public:
         Monitor();
-        virtual ~Monitor() {}
+        ~Monitor();
         DNSServiceRef *allocateServiceRef(int id, Context *c);
         void startMonitoring(int id);
         DNSServiceRef *lookupServiceRef(int id);
@@ -101,6 +102,7 @@ private:
         int mPollSize;
         int mCtrlSocketPair[2];
         pthread_mutex_t mHeadMutex;
+        std::thread* mRescanThread;
     };
 
     class Handler : public NetdCommand {