[2.27] libanl: properly cleanup if first helper thread creation failed (bug 22927)

[Florian Weimer]

From: Andreas Schwab <schwab@suse.de>

(cherry picked from commit bd3b0fbae33a9a4cc5e2daf049443d5cf03d4251)

2018-11-05  Andreas Schwab  <schwab@suse.de>

	[BZ #22927]
	* resolv/gai_misc.c (__gai_enqueue_request): Don't crash if
	creating the first helper thread failed.

diff --git a/NEWS b/NEWS
index c1102a152f..5fef60bc0f 100644
--- a/NEWS
+++ b/NEWS
@@ -65,6 +65,7 @@ The following bugs are resolved with this release:
   [22918] multiple common of `__nss_shadow_database'
   [22919] sparc32: backtrace yields infinite backtrace with makecontext
   [22926] FTBFS on powerpcspe
+  [22927] libanl: properly cleanup if first helper thread creation failed
   [22932] lt_LT: Update of abbreviated month names from CLDR required
   [22937] Greek (el_GR, el_CY) locales actually need ab_alt_mon
   [22947] FAIL: misc/tst-preadvwritev2
diff --git a/resolv/gai_misc.c b/resolv/gai_misc.c
index e7c3b63cc5..80a2cff835 100644
--- a/resolv/gai_misc.c
+++ b/resolv/gai_misc.c
@@ -261,8 +261,11 @@ __gai_enqueue_request (struct gaicb *gaicbp)
 	      /* We cannot create a thread in the moment and there is
 		 also no thread running.  This is a problem.  `errno' is
 		 set to EAGAIN if this is only a temporary problem.  */
-	      assert (lastp->next == newp);
-	      lastp->next = NULL;
+	      assert (requests == newp || lastp->next == newp);
+	      if (lastp != NULL)
+		lastp->next = NULL;
+	      else
+		requests = NULL;
 	      requests_tail = lastp;
 
 	      newp->next = freelist;