Bug 1696138 - Make a copy of the host before calling getaddrinfo r=necko-reviewers,kershaw

Differential Revision: https://phabricator.services.mozilla.com/D118010

modules/libpref/init/StaticPrefList.yaml

@@ -9315,6 +9315,13 @@
   value: true
   mirror: always
 
+# When this pref is true, we copy the host name to a fresh string before
+# calling into getaddrinfo.
+- name: network.dns.copy_string_before_call
+  type: RelaxedAtomicBool
+  value: true
+  mirror: always
+
 # The proxy type. See nsIProtocolProxyService.idl
 #     PROXYCONFIG_DIRECT   = 0
 #     PROXYCONFIG_MANUAL   = 1

netwerk/dns/GetAddrInfo.cpp

@@ -350,7 +350,14 @@ nsresult GetAddrInfo(const nsACString& aHost, uint16_t aAddressFamily,
     return (*aAddrInfo)->Addresses().Length() ? NS_OK : NS_ERROR_UNKNOWN_HOST;
   }
 
-  nsAutoCString host(aHost);
+  nsAutoCString host;
+  if (StaticPrefs::network_dns_copy_string_before_call()) {
+    host = Substring(aHost.BeginReading(), aHost.Length());
+    MOZ_ASSERT(aHost.BeginReading() != host.BeginReading());
+  } else {
+    host = aHost;
+  }
+
   if (gNativeIsLocalhost) {
     // pretend we use the given host but use IPv4 localhost instead!
     host = "localhost"_ns;