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glibc/resolv/res_init.c
Florian Weimer 446997ff14 resolv: Implement trust-ad option for /etc/resolv.conf [BZ #20358] 
This introduces a concept of trusted name servers, for which the
AD bit is passed through to applications.  For untrusted name
servers (the default), the AD bit in responses are cleared, to
provide a safe default.

This approach is very similar to the one suggested by Pavel Šimerda
in <https://bugzilla.redhat.com/show_bug.cgi?id=1164339#c15>.

The DNS test framework in support/ is enhanced with support for
setting the AD bit in responses.

Tested on x86_64-linux-gnu.

Change-Id: Ibfe0f7c73ea221c35979842c5c3b6ed486495ccc
2019-11-27 20:54:37 +01:00

713 lines
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/* Resolver state initialization and resolv.conf parsing.
Copyright (C) 1995-2019 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
<https://www.gnu.org/licenses/>. */
/*
* Copyright (c) 1985, 1989, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* Portions Copyright (c) 1993 by Digital Equipment Corporation.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies, and that
* the name of Digital Equipment Corporation not be used in advertising or
* publicity pertaining to distribution of the document or software without
* specific, written prior permission.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
* WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL DIGITAL EQUIPMENT
* CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
* DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
* PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
* ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
* SOFTWARE.
*/
/*
* Portions Copyright (c) 1996-1999 by Internet Software Consortium.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
* ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
* CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
* DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
* PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
* ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
* SOFTWARE.
*/
#include <ctype.h>
#include <netdb.h>
#include <resolv/resolv-internal.h>
#include <res_hconf.h>
#include <stdio.h>
#include <stdio_ext.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <net/if.h>
#include <netinet/in.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <inet/net-internal.h>
#include <errno.h>
#include <resolv_conf.h>
static uint32_t net_mask (struct in_addr);
int
res_ninit (res_state statp)
{
return __res_vinit (statp, 0);
}
libc_hidden_def (__res_ninit)
/* Return true if CH separates the netmask in the "sortlist"
directive. */
static inline bool
is_sort_mask (char ch)
{
return ch == '/' || ch == '&';
}
/* Array of name server addresses. */
#define DYNARRAY_STRUCT nameserver_list
#define DYNARRAY_ELEMENT const struct sockaddr *
#define DYNARRAY_ELEMENT_FREE(e) free ((struct sockaddr *) *(e))
#define DYNARRAY_INITIAL_SIZE 3
#define DYNARRAY_PREFIX nameserver_list_
#include <malloc/dynarray-skeleton.c>
/* Array of strings for the search array. The backing store is
managed separately. */
#define DYNARRAY_STRUCT search_list
#define DYNARRAY_ELEMENT const char *
#define DYNARRAY_INITIAL_SIZE 6
#define DYNARRAY_PREFIX search_list_
#include <malloc/dynarray-skeleton.c>
/* Array of name server addresses. */
#define DYNARRAY_STRUCT sort_list
#define DYNARRAY_ELEMENT struct resolv_sortlist_entry
#define DYNARRAY_INITIAL_SIZE 0
#define DYNARRAY_PREFIX sort_list_
#include <malloc/dynarray-skeleton.c>
/* resolv.conf parser state and results. */
struct resolv_conf_parser
{
char *buffer; /* Temporary buffer for reading lines. */
struct nameserver_list nameserver_list; /* Nameserver addresses. */
char *search_list_store; /* Backing storage for search list entries. */
struct search_list search_list; /* Points into search_list_store. */
struct sort_list sort_list; /* Address preference sorting list. */
/* Configuration template. The non-array elements are filled in
directly. The array elements are updated prior to the call to
__resolv_conf_attach. */
struct resolv_conf template;
};
/* Return true if *PREINIT contains actual preinitialization. */
static bool
has_preinit_values (const struct __res_state *preinit)
{
return (preinit->retrans != 0 && preinit->retrans != RES_TIMEOUT)
|| (preinit->retry != 0 && preinit->retry != RES_DFLRETRY)
|| (preinit->options != 0
&& (preinit->options & ~RES_INIT) != RES_DEFAULT);
}
static void
resolv_conf_parser_init (struct resolv_conf_parser *parser,
const struct __res_state *preinit)
{
parser->buffer = NULL;
parser->search_list_store = NULL;
nameserver_list_init (&parser->nameserver_list);
search_list_init (&parser->search_list);
sort_list_init (&parser->sort_list);
if (preinit != NULL)
{
parser->template.retrans = preinit->retrans;
parser->template.retry = preinit->retry;
parser->template.options = preinit->options | RES_INIT;
}
else
{
parser->template.retrans = RES_TIMEOUT;
parser->template.retry = RES_DFLRETRY;
parser->template.options = RES_DEFAULT | RES_INIT;
}
parser->template.ndots = 1;
}
static void
resolv_conf_parser_free (struct resolv_conf_parser *parser)
{
free (parser->buffer);
free (parser->search_list_store);
nameserver_list_free (&parser->nameserver_list);
search_list_free (&parser->search_list);
sort_list_free (&parser->sort_list);
}
/* Allocate a struct sockaddr_in object on the heap, with the
specified address and port. */
static struct sockaddr *
allocate_address_v4 (struct in_addr a, uint16_t port)
{
struct sockaddr_in *sa4 = malloc (sizeof (*sa4));
if (sa4 == NULL)
return NULL;
sa4->sin_family = AF_INET;
sa4->sin_addr = a;
sa4->sin_port = htons (port);
return (struct sockaddr *) sa4;
}
/* Try to obtain the domain name from the host name and store it in
*RESULT. Return false on memory allocation failure. If the domain
name cannot be determined for any other reason, write NULL to
*RESULT and return true. */
static bool
domain_from_hostname (char **result)
{
char buf[256];
/* gethostbyname may not terminate the buffer. */
buf[sizeof (buf) - 1] = '\0';
if (__gethostname (buf, sizeof (buf) - 1) == 0)
{
char *dot = strchr (buf, '.');
if (dot != NULL)
{
*result = __strdup (dot + 1);
if (*result == NULL)
return false;
return true;
}
}
*result = NULL;
return true;
}
static void res_setoptions (struct resolv_conf_parser *, const char *options);
/* Internal helper function for __res_vinit, to aid with resource
deallocation and error handling. Return true on success, false on
failure. */
static bool
res_vinit_1 (FILE *fp, struct resolv_conf_parser *parser)
{
char *cp;
size_t buffer_size = 0;
bool haveenv = false;
/* Allow user to override the local domain definition. */
if ((cp = getenv ("LOCALDOMAIN")) != NULL)
{
/* The code below splits the string in place. */
cp = __strdup (cp);
if (cp == NULL)
return false;
free (parser->search_list_store);
parser->search_list_store = cp;
haveenv = true;
/* The string will be truncated as needed below. */
search_list_add (&parser->search_list, cp);
/* Set search list to be blank-separated strings from rest of
env value. Permits users of LOCALDOMAIN to still have a
search list, and anyone to set the one that they want to use
as an individual (even more important now that the rfc1535
stuff restricts searches). */
for (bool in_name = true; *cp != '\0'; cp++)
{
if (*cp == '\n')
{
*cp = '\0';
break;
}
else if (*cp == ' ' || *cp == '\t')
{
*cp = '\0';
in_name = false;
}
else if (!in_name)
{
search_list_add (&parser->search_list, cp);
in_name = true;
}
}
}
#define MATCH(line, name) \
(!strncmp ((line), name, sizeof (name) - 1) \
&& ((line)[sizeof (name) - 1] == ' ' \
|| (line)[sizeof (name) - 1] == '\t'))
if (fp != NULL)
{
/* No threads use this stream. */
__fsetlocking (fp, FSETLOCKING_BYCALLER);
/* Read the config file. */
while (true)
{
{
ssize_t ret = __getline (&parser->buffer, &buffer_size, fp);
if (ret <= 0)
{
if (_IO_ferror_unlocked (fp))
return false;
else
break;
}
}
/* Skip comments. */
if (*parser->buffer == ';' || *parser->buffer == '#')
continue;
/* Read default domain name. */
if (MATCH (parser->buffer, "domain"))
{
if (haveenv)
/* LOCALDOMAIN overrides the configuration file. */
continue;
cp = parser->buffer + sizeof ("domain") - 1;
while (*cp == ' ' || *cp == '\t')
cp++;
if ((*cp == '\0') || (*cp == '\n'))
continue;
cp = __strdup (cp);
if (cp == NULL)
return false;
free (parser->search_list_store);
parser->search_list_store = cp;
search_list_clear (&parser->search_list);
search_list_add (&parser->search_list, cp);
/* Replace trailing whitespace. */
if ((cp = strpbrk (cp, " \t\n")) != NULL)
*cp = '\0';
continue;
}
/* Set search list. */
if (MATCH (parser->buffer, "search"))
{
if (haveenv)
/* LOCALDOMAIN overrides the configuration file. */
continue;
cp = parser->buffer + sizeof ("search") - 1;
while (*cp == ' ' || *cp == '\t')
cp++;
if ((*cp == '\0') || (*cp == '\n'))
continue;
{
char *p = strchr (cp, '\n');
if (p != NULL)
*p = '\0';
}
cp = __strdup (cp);
if (cp == NULL)
return false;
free (parser->search_list_store);
parser->search_list_store = cp;
/* The string is truncated below. */
search_list_clear (&parser->search_list);
search_list_add (&parser->search_list, cp);
/* Set search list to be blank-separated strings on rest
of line. */
for (bool in_name = true; *cp != '\0'; cp++)
{
if (*cp == ' ' || *cp == '\t')
{
*cp = '\0';
in_name = false;
}
else if (!in_name)
{
search_list_add (&parser->search_list, cp);
in_name = true;
}
}
continue;
}
/* Read nameservers to query. */
if (MATCH (parser->buffer, "nameserver"))
{
struct in_addr a;
cp = parser->buffer + sizeof ("nameserver") - 1;
while (*cp == ' ' || *cp == '\t')
cp++;
/* Ignore trailing contents on the name server line. */
{
char *el;
if ((el = strpbrk (cp, " \t\n")) != NULL)
*el = '\0';
}
struct sockaddr *sa;
if ((*cp != '\0') && (*cp != '\n') && __inet_aton_exact (cp, &a))
{
sa = allocate_address_v4 (a, NAMESERVER_PORT);
if (sa == NULL)
return false;
}
else
{
struct in6_addr a6;
char *el;
if ((el = strchr (cp, SCOPE_DELIMITER)) != NULL)
*el = '\0';
if ((*cp != '\0') && (__inet_pton (AF_INET6, cp, &a6) > 0))
{
struct sockaddr_in6 *sa6;
sa6 = malloc (sizeof (*sa6));
if (sa6 == NULL)
return false;
sa6->sin6_family = AF_INET6;
sa6->sin6_port = htons (NAMESERVER_PORT);
sa6->sin6_flowinfo = 0;
sa6->sin6_addr = a6;
sa6->sin6_scope_id = 0;
if (__glibc_likely (el != NULL))
/* Ignore errors, for backwards
compatibility. */
__inet6_scopeid_pton
(&a6, el + 1, &sa6->sin6_scope_id);
sa = (struct sockaddr *) sa6;
}
else
/* IPv6 address parse failure. */
sa = NULL;
}
if (sa != NULL)
{
const struct sockaddr **p = nameserver_list_emplace
(&parser->nameserver_list);
if (p != NULL)
*p = sa;
else
{
free (sa);
return false;
}
}
continue;
}
if (MATCH (parser->buffer, "sortlist"))
{
struct in_addr a;
cp = parser->buffer + sizeof ("sortlist") - 1;
while (true)
{
while (*cp == ' ' || *cp == '\t')
cp++;
if (*cp == '\0' || *cp == '\n' || *cp == ';')
break;
char *net = cp;
while (*cp && !is_sort_mask (*cp) && *cp != ';'
&& isascii (*cp) && !isspace (*cp))
cp++;
char separator = *cp;
*cp = 0;
struct resolv_sortlist_entry e;
if (__inet_aton_exact (net, &a))
{
e.addr = a;
if (is_sort_mask (separator))
{
*cp++ = separator;
net = cp;
while (*cp && *cp != ';'
&& isascii (*cp) && !isspace (*cp))
cp++;
separator = *cp;
*cp = 0;
if (__inet_aton_exact (net, &a))
e.mask = a.s_addr;
else
e.mask = net_mask (e.addr);
}
else
e.mask = net_mask (e.addr);
sort_list_add (&parser->sort_list, e);
}
*cp = separator;
}
continue;
}
if (MATCH (parser->buffer, "options"))
{
res_setoptions (parser, parser->buffer + sizeof ("options") - 1);
continue;
}
}
fclose (fp);
}
if (__glibc_unlikely (nameserver_list_size (&parser->nameserver_list) == 0))
{
const struct sockaddr **p
= nameserver_list_emplace (&parser->nameserver_list);
if (p == NULL)
return false;
*p = allocate_address_v4 (__inet_makeaddr (IN_LOOPBACKNET, 1),
NAMESERVER_PORT);
if (*p == NULL)
return false;
}
if (search_list_size (&parser->search_list) == 0)
{
char *domain;
if (!domain_from_hostname (&domain))
return false;
if (domain != NULL)
{
free (parser->search_list_store);
parser->search_list_store = domain;
search_list_add (&parser->search_list, domain);
}
}
if ((cp = getenv ("RES_OPTIONS")) != NULL)
res_setoptions (parser, cp);
if (nameserver_list_has_failed (&parser->nameserver_list)
|| search_list_has_failed (&parser->search_list)
|| sort_list_has_failed (&parser->sort_list))
{
__set_errno (ENOMEM);
return false;
}
return true;
}
struct resolv_conf *
__resolv_conf_load (struct __res_state *preinit)
{
/* Ensure that /etc/hosts.conf has been loaded (once). */
_res_hconf_init ();
FILE *fp = fopen (_PATH_RESCONF, "rce");
if (fp == NULL)
switch (errno)
{
case EACCES:
case EISDIR:
case ELOOP:
case ENOENT:
case ENOTDIR:
case EPERM:
/* Ignore these errors. They are persistent errors caused
by file system contents. */
break;
default:
/* Other errors refer to resource allocation problems and
need to be handled by the application. */
return NULL;
}
struct resolv_conf_parser parser;
resolv_conf_parser_init (&parser, preinit);
struct resolv_conf *conf = NULL;
if (res_vinit_1 (fp, &parser))
{
parser.template.nameserver_list
= nameserver_list_begin (&parser.nameserver_list);
parser.template.nameserver_list_size
= nameserver_list_size (&parser.nameserver_list);
parser.template.search_list = search_list_begin (&parser.search_list);
parser.template.search_list_size
= search_list_size (&parser.search_list);
parser.template.sort_list = sort_list_begin (&parser.sort_list);
parser.template.sort_list_size = sort_list_size (&parser.sort_list);
conf = __resolv_conf_allocate (&parser.template);
}
resolv_conf_parser_free (&parser);
return conf;
}
/* Set up default settings. If the /etc/resolv.conf configuration
file exist, the values there will have precedence. Otherwise, the
server address is set to INADDR_LOOPBACK and the default domain
name comes from gethostname. The RES_OPTIONS and LOCALDOMAIN
environment variables can be used to override some settings.
Return 0 if completes successfully, -1 on error. */
int
__res_vinit (res_state statp, int preinit)
{
struct resolv_conf *conf;
if (preinit && has_preinit_values (statp))
/* For the preinit case, we cannot use the cached configuration
because some settings could be different. */
conf = __resolv_conf_load (statp);
else
conf = __resolv_conf_get_current ();
if (conf == NULL)
return -1;
bool ok = __resolv_conf_attach (statp, conf);
__resolv_conf_put (conf);
if (ok)
{
if (preinit)
statp->id = res_randomid ();
return 0;
}
else
return -1;
}
static void
res_setoptions (struct resolv_conf_parser *parser, const char *options)
{
const char *cp = options;
while (*cp)
{
/* Skip leading and inner runs of spaces. */
while (*cp == ' ' || *cp == '\t')
cp++;
/* Search for and process individual options. */
if (!strncmp (cp, "ndots:", sizeof ("ndots:") - 1))
{
int i = atoi (cp + sizeof ("ndots:") - 1);
if (i <= RES_MAXNDOTS)
parser->template.ndots = i;
else
parser->template.ndots = RES_MAXNDOTS;
}
else if (!strncmp (cp, "timeout:", sizeof ("timeout:") - 1))
{
int i = atoi (cp + sizeof ("timeout:") - 1);
if (i <= RES_MAXRETRANS)
parser->template.retrans = i;
else
parser->template.retrans = RES_MAXRETRANS;
}
else if (!strncmp (cp, "attempts:", sizeof ("attempts:") - 1))
{
int i = atoi (cp + sizeof ("attempts:") - 1);
if (i <= RES_MAXRETRY)
parser->template.retry = i;
else
parser->template.retry = RES_MAXRETRY;
}
else
{
static const struct
{
char str[22];
uint8_t len;
uint8_t clear;
unsigned long int flag;
} options[] = {
#define STRnLEN(str) str, sizeof (str) - 1
{ STRnLEN ("rotate"), 0, RES_ROTATE },
{ STRnLEN ("edns0"), 0, RES_USE_EDNS0 },
{ STRnLEN ("single-request-reopen"), 0, RES_SNGLKUPREOP },
{ STRnLEN ("single-request"), 0, RES_SNGLKUP },
{ STRnLEN ("no_tld_query"), 0, RES_NOTLDQUERY },
{ STRnLEN ("no-tld-query"), 0, RES_NOTLDQUERY },
{ STRnLEN ("no-reload"), 0, RES_NORELOAD },
{ STRnLEN ("use-vc"), 0, RES_USEVC },
{ STRnLEN ("trust-ad"), 0, RES_TRUSTAD },
};
#define noptions (sizeof (options) / sizeof (options[0]))
for (int i = 0; i < noptions; ++i)
if (strncmp (cp, options[i].str, options[i].len) == 0)
{
if (options[i].clear)
parser->template.options &= options[i].flag;
else
parser->template.options |= options[i].flag;
break;
}
}
/* Skip to next run of spaces. */
while (*cp && *cp != ' ' && *cp != '\t')
cp++;
}
}
static uint32_t
net_mask (struct in_addr in)
{
uint32_t i = ntohl (in.s_addr);
if (IN_CLASSA (i))
return htonl (IN_CLASSA_NET);
else if (IN_CLASSB (i))
return htonl (IN_CLASSB_NET);
return htonl (IN_CLASSC_NET);
}
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