[PATCH] [BZ #17977] Fix potential hanging of gethostbyaddr_r/gethostbyname_r

["Dmitry V. Levin" <ldv at altlinux dot org>]

[BZ #17977]
* resolv/res_hconf.c (_res_hconf_reorder_addrs): Fix unlocking
when initializing interface list.
* 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.
---
 ChangeLog                      | 12 ++++++
 NEWS                           | 20 ++++-----
 resolv/res_hconf.c             |  6 +--
 resolv/tst-res_hconf_reorder.c | 95 ++++++++++++++++++++++++++++++++++++++++++
 resolv/Makefile                |  4 ++
 5 files changed, 124 insertions(+), 13 deletions(-)
 create mode 100644 resolv/tst-res_hconf_reorder.c

diff --git a/resolv/res_hconf.c b/resolv/res_hconf.c
index b9c229d..0d4f3f4 100644
--- a/resolv/res_hconf.c
+++ b/resolv/res_hconf.c
@@ -421,7 +421,7 @@ _res_hconf_reorder_addrs (struct hostent *hp)
       /* Get lock.  */
       __libc_lock_lock (lock);
 
-      /* Recheck, somebody else might have done the work by done.  */
+      /* Recheck, somebody else might have done the work by now.  */
       if (num_ifs <= 0)
 	{
 	  int new_num_ifs = 0;
@@ -473,10 +473,10 @@ _res_hconf_reorder_addrs (struct hostent *hp)
 	  errno = save;
 
 	  num_ifs = new_num_ifs;
-
-	  __libc_lock_unlock (lock);
 	}
 
+      __libc_lock_unlock (lock);
+
       __close (sd);
     }
 
diff --git a/resolv/tst-res_hconf_reorder.c b/resolv/tst-res_hconf_reorder.c
new file mode 100644
index 0000000..e874d94
--- /dev/null
+++ b/resolv/tst-res_hconf_reorder.c
@@ -0,0 +1,95 @@
+/* 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 <error.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;
+
+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;
+
+  ts.tv_nsec = 100000000;
+
+  for (i = 0; i < N; ++i)
+    {
+      int rc = pthread_create (&thr[i], NULL, resolve, NULL);
+
+      if (rc)
+	error (1, rc, "pthread_create");
+    }
+
+  for (i = 0; i < N; ++i)
+    {
+      void *retval;
+      int rc = pthread_join (thr[i], &retval);
+
+      if (rc)
+	error (1, rc, "pthread_join");
+      if (retval)
+	result = 1;
+    }
+
+  ts.tv_nsec = 0;
+
+  return result;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/resolv/Makefile b/resolv/Makefile
index f62eea4..3509d98 100644
--- a/resolv/Makefile
+++ b/resolv/Makefile
@@ -39,6 +39,7 @@ 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	\
@@ -98,6 +99,9 @@ $(objpfx)libanl.so: $(shared-thread-library)
 
 $(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.out: $(objpfx)tst-leaks.out

-- 
ldv