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resolv: Fix improper assert in __resolv_conf_attach

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This commit is contained in:
Florian Weimer 2017-07-04 11:18:34 +02:00
parent e237357a5a
commit 89f6307c5d
4 changed files with 108 additions and 8 deletions
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9
ChangeLog
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@ -1,3 +1,12 @@
2017-07-04 Florian Weimer <fweimer@redhat.com>
* resolv/resolv_conf.c (struct resolv_conf_global): Clarify free
list management and the role of free_list_start.
(decrement_at_index): Put zero at the end of the free list.
(__resolv_conf_attach): Fix bogus assert.
* resolv/Makefile (tests): Add tst-resolv-res_init-multi.
(tst-resolv-res_init-multi): Link with -lresolv, -lpthread.
2017-07-03 Florian Weimer <fweimer@redhat.com>
resolv: Introduce free list for resolv_conf index slosts.

3
resolv/Makefile
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@ -51,6 +51,7 @@ tests += \
tst-resolv-basic \
tst-resolv-edns \
tst-resolv-network \
tst-resolv-res_init-multi \
tst-resolv-search \
# These tests need libdl.
@ -160,6 +161,8 @@ $(objpfx)tst-resolv-basic: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-edns: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-network: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-res_init: $(libdl) $(objpfx)libresolv.so
$(objpfx)tst-resolv-res_init-multi: $(objpfx)libresolv.so \
$(shared-thread-library)
$(objpfx)tst-resolv-res_init-thread: $(libdl) $(objpfx)libresolv.so \
$(shared-thread-library)
$(objpfx)tst-resolv-qtypes: $(objpfx)libresolv.so $(shared-thread-library)

15
resolv/resolv_conf.c
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@ -58,8 +58,10 @@ struct resolv_conf_global
the array element is overwritten with NULL. */
struct resolv_conf_array array;
/* Start of the free list in the array. The MSB is set if this
field has been initialized. */
/* Start of the free list in the array. Zero if the free list is
empty. Otherwise, free_list_start >> 1 is the first element of
the free list (and the free list entries all have their LSB set
and are shifted one to the left). */
uintptr_t free_list_start;
/* Cached current configuration object for /etc/resolv.conf. */
@ -567,11 +569,7 @@ decrement_at_index (struct resolv_conf_global *global_copy, size_t index)
struct resolv_conf *conf = (struct resolv_conf *) *slot;
conf_decrement (conf);
/* Put the slot onto the free list. */
if (global_copy->free_list_start == 0)
/* Not yet initialized. */
*slot = 1;
else
*slot = global_copy->free_list_start;
*slot = global_copy->free_list_start;
global_copy->free_list_start = (index << 1) | 1;
}
}
@ -598,7 +596,8 @@ __resolv_conf_attach (struct __res_state *resp, struct resolv_conf *conf)
index = global_copy->free_list_start >> 1;
uintptr_t *slot = resolv_conf_array_at (&global_copy->array, index);
global_copy->free_list_start = *slot;
assert (global_copy->free_list_start & 1);
assert (global_copy->free_list_start == 0
|| global_copy->free_list_start & 1);
/* Install the configuration pointer. */
*slot = (uintptr_t) conf;
}

89
resolv/tst-resolv-res_init-multi.c Normal file
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@ -0,0 +1,89 @@
/* Multi-threaded test for resolver initialization.
Copyright (C) 2017 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 <netdb.h>
#include <resolv.h>
#include <stdlib.h>
#include <support/check.h>
#include <support/support.h>
#include <support/xthread.h>
/* Whether name lookups succeed does not really matter. We use this
to trigger initialization of the resolver. */
static const char *test_hostname = "www.gnu.org";
/* The different initialization methods. */
enum test_type { init, byname, gai };
enum { type_count = 3 };
/* Thread function. Perform a few resolver options. */
static void *
thread_func (void *closure)
{
enum test_type *ptype = closure;
/* Perform a few calls to the requested operation. */
TEST_VERIFY (*ptype >= 0);
TEST_VERIFY (*ptype < (int) type_count);
for (int i = 0; i < 3; ++i)
switch (*ptype)
{
case init:
res_init ();
break;
case byname:
gethostbyname (test_hostname);
break;
case gai:
{
struct addrinfo hints = { 0, };
struct addrinfo *ai = NULL;
if (getaddrinfo (test_hostname, "80", &hints, &ai) == 0)
freeaddrinfo (ai);
}
break;
}
free (ptype);
return NULL;
}
static int
do_test (void)
{
/* Start a small number of threads which perform resolver
operations. */
enum { thread_count = 30 };
pthread_t threads[thread_count];
for (int i = 0; i < thread_count; ++i)
{
enum test_type *ptype = xmalloc (sizeof (*ptype));
*ptype = i % type_count;
threads[i] = xpthread_create (NULL, thread_func, ptype);
}
for (int i = 0; i < type_count; ++i)
{
enum test_type *ptype = xmalloc (sizeof (*ptype));
*ptype = i;
thread_func (ptype);
}
for (int i = 0; i < thread_count; ++i)
xpthread_join (threads[i]);
return 0;
}
#include <support/test-driver.c>