Bug 1950136 - add guards for res_ninit and res_nclose. r=necko-reviewers,kershaw

Differential Revision: https://phabricator.services.mozilla.com/D244737

netwerk/dns/PlatformDNSUnix.cpp

@@ -9,6 +9,7 @@
 #include "mozilla/net/DNSPacket.h"
 #include "nsIDNSService.h"
 #include "mozilla/Maybe.h"
+#include "mozilla/Mutex.h"
 #include "mozilla/StaticPrefs_network.h"
 #include "mozilla/ThreadLocal.h"
 
@@ -22,6 +23,7 @@ namespace mozilla::net {
 
 #if defined(HAVE_RES_NINIT)
 MOZ_THREAD_LOCAL(struct __res_state*) sThreadRes;
+mozilla::StaticMutex sMutex MOZ_UNANNOTATED;
 #endif
 
 #define LOG(msg, ...) \
@@ -44,10 +46,13 @@ nsresult ResolveHTTPSRecordImpl(const nsACString& aHost,
   if (!sThreadRes.get()) {
     UniquePtr<struct __res_state> resState(new struct __res_state);
     memset(resState.get(), 0, sizeof(struct __res_state));
+    {
+      StaticMutexAutoLock lock(sMutex);
       if (int ret = res_ninit(resState.get())) {
         LOG("res_ninit failed: %d", ret);
         return NS_ERROR_UNKNOWN_HOST;
       }
+    }
     sThreadRes.set(resState.release());
   }
 #endif
@@ -90,7 +95,10 @@ void DNSThreadShutdown() {
   }
 
   sThreadRes.set(nullptr);
+  {
+    StaticMutexAutoLock lock(sMutex);
     res_nclose(res);
+  }
   free(res);
 #endif
 }