commit b57525f1a376149840f740a31535681c07152ba4

Author: Dmitry V. Levin <ldv@altlinux.org>

Date:   Thu Jun 18 21:40:46 2015 +0000

    Fix potential hanging of gethostbyaddr_r/gethostbyname_r

    When "reorder" resolver option is enabled, threads of a multi-threaded

    process could hang in gethostbyaddr_r, gethostbyname_r, or

    gethostbyname2_r.

    Due to a trivial bug in _res_hconf_reorder_addrs, simultaneous

    invocations of this function in a multi-threaded process could result to

    _res_hconf_reorder_addrs returning without releasing the lock it holds,

    causing other threads to block indefinitely while waiting for the lock

    that is not going to be released.

    [BZ #17977]

    * resolv/res_hconf.c (_res_hconf_reorder_addrs): Fix unlocking

    when initializing interface list, based on the bug analysis

    and the patch proposed by Eric Newton.

    * resolv/tst-res_hconf_reorder.c: New test.

    * resolv/Makefile [$(have-thread-library) = yes] (tests): Add

    tst-res_hconf_reorder.

    ($(objpfx)tst-res_hconf_reorder): Depend on $(libdl)

    and $(shared-thread-library).

    (tst-res_hconf_reorder-ENV): New variable.

Index: glibc-2.17-c758a686/resolv/Makefile

===================================================================

--- glibc-2.17-c758a686.orig/resolv/Makefile

+++ glibc-2.17-c758a686/resolv/Makefile

@@ -40,6 +40,7 @@ extra-libs := libresolv libnss_dns

 ifeq ($(have-thread-library),yes)

 extra-libs += libanl

 routines += gai_sigqueue

+tests += tst-res_hconf_reorder

 endif

 extra-libs-others = $(extra-libs)

 libresolv-routines := gethnamaddr res_comp res_debug	\

@@ -108,6 +108,9 @@ $(objpfx)libanl.so: $(common-objpfx)libc

 $(objpfx)ga_test: $(objpfx)libanl.so $(shared-thread-library)

+$(objpfx)tst-res_hconf_reorder: $(libdl) $(shared-thread-library)

+tst-res_hconf_reorder-ENV = RESOLV_REORDER=on

+

 $(objpfx)tst-leaks: $(objpfx)libresolv.so

 tst-leaks-ENV = MALLOC_TRACE=$(objpfx)tst-leaks.mtrace

 $(objpfx)mtrace-tst-leaks: $(objpfx)tst-leaks.out

Index: glibc-2.17-c758a686/resolv/res_hconf.c

===================================================================

--- glibc-2.17-c758a686.orig/resolv/res_hconf.c

+++ glibc-2.17-c758a686/resolv/res_hconf.c

@@ -462,10 +462,10 @@ _res_hconf_reorder_addrs (struct hostent

 	  errno = save;

 	  num_ifs = new_num_ifs;

-

-	  __libc_lock_unlock (lock);

 	}

+      __libc_lock_unlock (lock);

+

       __close (sd);

     }

Index: glibc-2.17-c758a686/resolv/tst-res_hconf_reorder.c

===================================================================

--- /dev/null

+++ glibc-2.17-c758a686/resolv/tst-res_hconf_reorder.c

@@ -0,0 +1,112 @@

+/* BZ #17977 _res_hconf_reorder_addrs test.

+

+   Copyright (C) 2015 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/>.  */

+

+#include <errno.h>

+#include <stdio.h>

+#include <string.h>

+#include <time.h>

+#include <dlfcn.h>

+#include <pthread.h>

+#include <netdb.h>

+#include <netinet/in.h>

+#include <sys/socket.h>

+

+static struct timespec ts;

+

+/* The first thread that gets a lock in _res_hconf_reorder_addrs()

+   should hold the lock long enough to make two other threads blocked.

+   This is achieved by slowing down realloc(3) that is called several times

+   by _res_hconf_reorder_addrs().  */

+

+void *

+realloc (void *ptr, size_t len)

+{

+  static void *(*fun) (void *, size_t);

+

+  if (!fun)

+    fun = dlsym (RTLD_NEXT, "realloc");

+

+  if (ts.tv_nsec)

+    nanosleep (&ts, NULL);

+

+  return (*fun) (ptr, len);

+}

+

+static void *

+resolve (void *arg)

+{

+  struct in_addr addr;

+  struct hostent ent;

+  struct hostent *result;

+  int err;

+  char buf[1024];

+

+  addr.s_addr = htonl (INADDR_LOOPBACK);

+  (void) gethostbyaddr_r ((void *) &addr, sizeof (addr), AF_INET,

+		          &ent, buf, sizeof (buf), &result, &err;;

+  return arg;

+}

+

+static int

+do_test (void)

+{

+  #define N 3

+  pthread_t thr[N];

+  unsigned int i;

+  int result = 0;

+

+  /* turn on realloc slowdown */

+  ts.tv_nsec = 100000000;

+

+  for (i = 0; i < N; ++i)

+    {

+      int rc = pthread_create (&thr[i], NULL, resolve, NULL);

+

+      if (rc)

+	{

+	  printf ("pthread_create: %s\n", strerror(rc));

+	  exit (1);

+	}

+    }

+

+  for (i = 0; i < N; ++i)

+    {

+      void *retval;

+      int rc = pthread_join (thr[i], &retval);

+

+      if (rc)

+	{

+	  printf ("pthread_join: %s\n", strerror(rc));

+	  exit (1);

+	}

+      if (retval)

+	{

+	  printf ("thread %u exit status %p\n", i, retval);

+	  result = 1;

+	}

+    }

+

+  /* turn off realloc slowdown, no longer needed */

+  ts.tv_nsec = 0;

+

+  return result;

+}

+

+#define TEST_FUNCTION do_test ()

+#include "../test-skeleton.c"