Add deferred cancellation regression test for getpwuid_r.

The fix in commit 312be3f9f5 resolved
several cancellation issues in several APIs.  This regression test is
designed to double check that at least getpwuid_r remainds correctly
implemented and does not provide additional unintended cancellation
points that may leave locks in an inconsistent state.

ChangeLog

@@ -1,5 +1,9 @@
 2016-12-24  Carlos O'Donell  <carlos@redhat.com>
 
+	* nss/Makefile [ifeq (yes,$(have-thread-library))]
+	(tests): Add tst-cancel-getpwuid_r.
+	* nss/tst-cancel-getpwuid_r.c: New file.
+
 	[BZ #11941]
 	* elf/dl-close.c (_dl_close): Take dl_load_lock to examine map.
 	Remove assert (map->l_init_called); if DF_1_NODELETE is set.

nss/Makefile

@@ -54,6 +54,12 @@ tests			= test-netdb tst-nss-test1 test-digits-dots \
 			  $(tests-static)
 xtests			= bug-erange
 
+# If we have a thread library then we can test cancellation against
+# some routines like getpwuid_r.
+ifeq (yes,$(have-thread-library))
+tests += tst-cancel-getpwuid_r
+endif
+
 # Specify rules for the nss_* modules.  We have some services.
 services		:= files db
 
@@ -125,3 +131,7 @@ $(objpfx)/libnss_test1.so$(libnss_test1.so-version): $(objpfx)/libnss_test1.so
 	$(make-link)
 endif
 $(objpfx)tst-nss-test1.out: $(objpfx)/libnss_test1.so$(libnss_test1.so-version)
+
+ifeq (yes,$(have-thread-library))
+$(objpfx)tst-cancel-getpwuid_r: $(shared-thread-library)
+endif

nss/tst-cancel-getpwuid_r.c

@@ -0,0 +1,180 @@
+/* Test cancellation of getpwuid_r.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Test if cancellation of getpwuid_r incorrectly leaves internal
+   function state locked resulting in hang of subsequent calls to
+   getpwuid_r.  The main thread creates a second thread which will do
+   the calls to getpwuid_r.  A semaphore is used by the second thread to
+   signal to the main thread that it is as close as it can be to the
+   call site of getpwuid_r.  The goal of the semaphore is to avoid any
+   cancellable function calls between the sem_post and the call to
+   getpwuid_r.  The main thread then attempts to cancel the second
+   thread.  Without the fixes the cancellation happens at any number of
+   calls to cancellable functions in getpuid_r, but with the fix the
+   cancellation either does not happen or happens only at expected
+   points where the internal state is consistent.  We use an explicit
+   pthread_testcancel call to terminate the loop in a timely fashion
+   if the implementation does not have a cancellation point.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <pwd.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <semaphore.h>
+#include <errno.h>
+#include <support/support.h>
+
+sem_t started;
+char *wbuf;
+long wbufsz;
+
+void
+worker_free (void *arg)
+{
+  free (arg);
+}
+
+static void *
+worker (void *arg)
+{
+  int ret;
+  unsigned int iter = 0;
+  struct passwd pwbuf, *pw;
+  uid_t uid;
+
+  uid = geteuid ();
+
+  /* Use a reasonable sized buffer.  Note that _SC_GETPW_R_SIZE_MAX is
+     just a hint and not any kind of maximum value.  */
+  wbufsz = sysconf (_SC_GETPW_R_SIZE_MAX);
+  if (wbufsz == -1)
+    wbufsz = 1024;
+  wbuf = xmalloc (wbufsz);
+
+  pthread_cleanup_push (worker_free, wbuf);
+  sem_post (&started);
+  while (1)
+    {
+      iter++;
+
+      ret = getpwuid_r (uid, &pwbuf, wbuf, wbufsz, &pw);
+
+      /* The call to getpwuid_r may not cancel so we need to test
+	 for cancellation after some number of iterations of the
+	 function.  Choose an arbitrary 100,000 iterations of running
+	 getpwuid_r in a tight cancellation loop before testing for
+	 cancellation.  */
+      if (iter > 100000)
+	pthread_testcancel ();
+
+      if (ret == ERANGE)
+	{
+	  /* Increase the buffer size.  */
+	  free (wbuf);
+	  wbufsz = wbufsz * 2;
+	  wbuf = xmalloc (wbufsz);
+	}
+
+    }
+  pthread_cleanup_pop (1);
+
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  int ret;
+  char *buf;
+  long bufsz;
+  void *retval;
+  struct passwd pwbuf, *pw;
+  pthread_t thread;
+
+  /* Configure the test to only use files. We control the files plugin
+     as part of glibc so we assert that it should be deferred
+     cancellation safe.  */
+  __nss_configure_lookup ("passwd", "files");
+
+  /* Use a reasonable sized buffer.  Note that  _SC_GETPW_R_SIZE_MAX is
+     just a hint and not any kind of maximum value.  */
+  bufsz = sysconf (_SC_GETPW_R_SIZE_MAX);
+  if (bufsz == -1)
+    bufsz = 1024;
+  buf = xmalloc (bufsz);
+
+  sem_init (&started, 0, 0);
+
+  pthread_create (&thread, NULL, worker, NULL);
+
+  do
+  {
+    ret = sem_wait (&started);
+    if (ret == -1 && errno != EINTR)
+      {
+        printf ("FAIL: Failed to wait for second thread to start.\n");
+	exit (EXIT_FAILURE);
+      }
+  }
+  while (ret != 0);
+
+  printf ("INFO: Cancelling thread\n");
+  if ((ret = pthread_cancel (thread)) != 0)
+    {
+      printf ("FAIL: Failed to cancel thread. Returned %d\n", ret);
+      exit (EXIT_FAILURE);
+    }
+
+  printf ("INFO: Joining...\n");
+  pthread_join (thread, &retval);
+  if (retval != PTHREAD_CANCELED)
+    {
+      printf ("FAIL: Thread was not cancelled.\n");
+      exit (EXIT_FAILURE);
+    }
+  printf ("INFO: Joined, trying getpwuid_r call\n");
+
+  /* Before the fix in 312be3f9f5eab1643d7dcc7728c76d413d4f2640 for this
+     issue the cancellation point could happen in any number of internal
+     calls, and therefore locks would be left held and the following
+     call to getpwuid_r would block and the test would time out.  */
+  do
+    {
+      ret = getpwuid_r (geteuid (), &pwbuf, buf, bufsz, &pw);
+      if (ret == ERANGE)
+	{
+	  /* Increase the buffer size.  */
+	  free (buf);
+	  bufsz = bufsz * 2;
+	  buf = xmalloc (bufsz);
+	}
+    }
+  while (ret == ERANGE);
+
+  free (buf);
+
+  /* Before the fix we would never get here.  */
+  printf ("PASS: Canceled getpwuid_r successfully"
+	  " and called it again without blocking.\n");
+
+  return 0;
+}
+
+#include <support/test-driver.c>