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Fix potential hanging of gethostbyaddr_r/gethostbyname_r

Browse Source 
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.
This commit is contained in:
Dmitry V. Levin 2015-06-18 21:40:46 +00:00
parent 47852c972d
commit b57525f1a3
5 changed files with 139 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
ChangeLog
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@ -1,5 +1,16 @@
2015-06-23 Dmitry V. Levin <ldv@altlinux.org>
[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.
* resolv/res_hconf.c (_res_hconf_reorder_addrs): Fix typo
in comment.

20
NEWS
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@ -14,16 +14,16 @@ Version 2.22
16560, 16704, 16783, 16850, 17053, 17090, 17195, 17269, 17293, 17322,
17523, 17542, 17569, 17581, 17588, 17596, 17620, 17621, 17628, 17631,
17692, 17711, 17715, 17776, 17779, 17792, 17836, 17912, 17916, 17930,
17932, 17944, 17949, 17964, 17965, 17967, 17969, 17978, 17987, 17991,
17996, 17998, 17999, 18007, 18019, 18020, 18029, 18030, 18032, 18034,
18036, 18038, 18039, 18042, 18043, 18046, 18047, 18049, 18068, 18080,
18093, 18100, 18104, 18110, 18111, 18116, 18125, 18128, 18138, 18185,
18196, 18197, 18206, 18210, 18211, 18217, 18220, 18221, 18234, 18244,
18247, 18287, 18319, 18324, 18333, 18346, 18397, 18409, 18410, 18412,
18418, 18422, 18434, 18444, 18468, 18469, 18470, 18479, 18483, 18495,
18496, 18497, 18498, 18507, 18512, 18513, 18519, 18520, 18522, 18527,
18528, 18529, 18530, 18532, 18533, 18534, 18536, 18539, 18540, 18542,
18544, 18545, 18546, 18547, 18553, 18558, 18569.
17932, 17944, 17949, 17964, 17965, 17967, 17969, 17977, 17978, 17987,
17991, 17996, 17998, 17999, 18007, 18019, 18020, 18029, 18030, 18032,
18034, 18036, 18038, 18039, 18042, 18043, 18046, 18047, 18049, 18068,
18080, 18093, 18100, 18104, 18110, 18111, 18116, 18125, 18128, 18138,
18185, 18196, 18197, 18206, 18210, 18211, 18217, 18220, 18221, 18234,
18244, 18247, 18287, 18319, 18324, 18333, 18346, 18397, 18409, 18410,
18412, 18418, 18422, 18434, 18444, 18468, 18469, 18470, 18479, 18483,
18495, 18496, 18497, 18498, 18507, 18512, 18513, 18519, 18520, 18522,
18527, 18528, 18529, 18530, 18532, 18533, 18534, 18536, 18539, 18540,
18542, 18544, 18545, 18546, 18547, 18553, 18558, 18569.
* Cache information can be queried via sysconf() function on s390 e.g. with
_SC_LEVEL1_ICACHE_SIZE as argument.

4
resolv/Makefile
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@ -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

4
resolv/res_hconf.c
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@ -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);
}

112
resolv/tst-res_hconf_reorder.c Normal file
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@ -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"