Backed out changeset 10479ec2f64e (bug 1853497) for causing process crashes in libresolv.so.

netwerk/dns/nsHostResolver.cpp

@@ -10,13 +10,13 @@
 #  include <arpa/inet.h>
 #  include <arpa/nameser.h>
 #  include <resolv.h>
+#  define RES_RETRY_ON_FAILURE
 #endif
 
 #include <stdlib.h>
 #include <ctime>
 #include "nsHostResolver.h"
 #include "nsError.h"
-#include "nsIOService.h"
 #include "nsISupports.h"
 #include "nsISupportsUtils.h"
 #include "nsIThreadManager.h"
@@ -98,54 +98,45 @@ LazyLogModule gHostResolverLog("nsHostResolver");
 
 //----------------------------------------------------------------------------
 
-#if defined(HAVE_RES_NINIT)
+#if defined(RES_RETRY_ON_FAILURE)
 
-// The nsResState class manages the res state.
-// This class ensures the resolver state is reset based on network change events
-// to maintain correct DNS resolutions.
-class MOZ_STACK_CLASS nsResState {
+// this class represents the resolver state for a given thread.  if we
+// encounter a lookup failure, then we can invoke the Reset method on an
+// instance of this class to reset the resolver (in case /etc/resolv.conf
+// for example changed).  this is mainly an issue on GNU systems since glibc
+// only reads in /etc/resolv.conf once per thread.  it may be an issue on
+// other systems as well.
+
+class nsResState {
  public:
-  // Set mLastReset to now, which should be larger than last network change
-  // time, so we won't reset when the thread just started.
-  nsResState() : mLastReset(PR_IntervalNow()) {}
+  nsResState()
+      // initialize mLastReset to the time when this object
+      // is created.  this means that a reset will not occur
+      // if a thread is too young.  the alternative would be
+      // to initialize this to the beginning of time, so that
+      // the first failure would cause a reset, but since the
+      // thread would have just started up, it likely would
+      // already have current /etc/resolv.conf info.
+      : mLastReset(PR_IntervalNow()) {}
 
-  ~nsResState() {
-    if (_res.options & RES_INIT) {
-      res_nclose(&_res);
-    }
-  }
-
-  void Init() {
-    if (!(_res.options & RES_INIT)) {
-      auto result = res_ninit(&_res);
-      LOG(("nsResState > 'res_ninit' returned %d ", result));
-    }
-  }
-
-  void MaybeReset() {
-    if (mLastReset > gIOService->LastNetworkLinkChange()) {
-      return;
-    }
-
-    PRIntervalTime now = PR_IntervalNow();
+  bool Reset() {
     // reset no more than once per second
-    if (PR_IntervalToSeconds(now - mLastReset) < 1) {
-      return;
+    if (PR_IntervalToSeconds(PR_IntervalNow() - mLastReset) < 1) {
+      return false;
     }
 
-    if (_res.options & RES_INIT) {
-      res_nclose(&_res);
-    }
+    mLastReset = PR_IntervalNow();
+    auto result = res_ninit(&_res);
 
-    mLastReset = now;
-    Init();
+    LOG(("nsResState::Reset() > 'res_ninit' returned %d", result));
+    return (result == 0);
   }
 
  private:
   PRIntervalTime mLastReset;
 };
 
-#endif  // HAVE_RES_NINIT
+#endif  // RES_RETRY_ON_FAILURE
 
 class DnsThreadListener final : public nsIThreadPoolListener {
   NS_DECL_THREADSAFE_ISUPPORTS
@@ -233,6 +224,19 @@ nsresult nsHostResolver::Init() MOZ_NO_THREAD_SAFETY_ANALYSIS {
                          "Could not register DNS pref callback.");
   }
 
+#if defined(HAVE_RES_NINIT)
+  // We want to make sure the system is using the correct resolver settings,
+  // so we force it to reload those settings whenever we startup a subsequent
+  // nsHostResolver instance.  We assume that there is no reason to do this
+  // for the first nsHostResolver instance since that is usually created
+  // during application startup.
+  static int initCount = 0;
+  if (initCount++ > 0) {
+    auto result = res_ninit(&_res);
+    LOG(("nsHostResolver::Init > 'res_ninit' returned %d", result));
+  }
+#endif
+
   // We can configure the threadpool to keep threads alive for a while after
   // the last ThreadFunc task has been executed.
   int32_t poolTimeoutSecs = Preferences::GetInt(kPrefThreadIdleTime, 60);
@@ -1841,9 +1845,8 @@ size_t nsHostResolver::SizeOfIncludingThis(MallocSizeOf mallocSizeOf) const {
 void nsHostResolver::ThreadFunc() {
   LOG(("DNS lookup thread - starting execution.\n"));
 
-#if defined(HAVE_RES_NINIT)
+#if defined(RES_RETRY_ON_FAILURE)
   nsResState rs;
-  rs.Init();
 #endif
   RefPtr<nsHostRecord> rec;
   RefPtr<AddrInfo> ai;
@@ -1884,11 +1887,14 @@ void nsHostResolver::ThreadFunc() {
       continue;
     }
 
-#if defined(HAVE_RES_NINIT)
-    rs.MaybeReset();
-#endif
     nsresult status =
         GetAddrInfo(rec->host, rec->af, rec->flags, getter_AddRefs(ai), getTtl);
+#if defined(RES_RETRY_ON_FAILURE)
+    if (NS_FAILED(status) && rs.Reset()) {
+      status = GetAddrInfo(rec->host, rec->af, rec->flags, getter_AddRefs(ai),
+                           getTtl);
+    }
+#endif
 
     mozilla::glean::networking::dns_native_count
         .EnumGet(rec->pb ? glean::networking::DnsNativeCountLabel::ePrivate