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"