[linux-2.6-block.git] / net / dns_resolver / dns_key.c

/* Key type used to cache DNS lookups made by the kernel
 *
 * See Documentation/networking/dns_resolver.rst
 *
 *   Copyright (c) 2007 Igor Mammedov
 *   Author(s): Igor Mammedov (niallain@gmail.com)
 *              Steve French (sfrench@us.ibm.com)
 *              Wang Lei (wang840925@gmail.com)
 *		David Howells (dhowells@redhat.com)
 *
 *   This 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.
 *
 *   This 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 this library; if not, see <http://www.gnu.org/licenses/>.
 */
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/keyctl.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <linux/dns_resolver.h>
#include <keys/dns_resolver-type.h>
#include <keys/user-type.h>
#include "internal.h"

MODULE_DESCRIPTION("DNS Resolver");
MODULE_AUTHOR("Wang Lei");
MODULE_LICENSE("GPL");

unsigned int dns_resolver_debug;
module_param_named(debug, dns_resolver_debug, uint, 0644);
MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");

const struct cred *dns_resolver_cache;

#define	DNS_ERRORNO_OPTION	"dnserror"

/*
 * Preparse instantiation data for a dns_resolver key.
 *
 * For normal hostname lookups, the data must be a NUL-terminated string, with
 * the NUL char accounted in datalen.
 *
 * If the data contains a '#' characters, then we take the clause after each
 * one to be an option of the form 'key=value'.  The actual data of interest is
 * the string leading up to the first '#'.  For instance:
 *
 *        "ip1,ip2,...#foo=bar"
 *
 * For server list requests, the data must begin with a NUL char and be
 * followed by a byte indicating the version of the data format.  Version 1
 * looks something like (note this is packed):
 *
 *	u8      Non-string marker (ie. 0)
 *	u8	Content (DNS_PAYLOAD_IS_*)
 *	u8	Version (e.g. 1)
 *	u8	Source of server list
 *	u8	Lookup status of server list
 *	u8	Number of servers
 *	foreach-server {
 *		__le16	Name length
 *		__le16	Priority (as per SRV record, low first)
 *		__le16	Weight (as per SRV record, higher first)
 *		__le16	Port
 *		u8	Source of address list
 *		u8	Lookup status of address list
 *		u8	Protocol (DNS_SERVER_PROTOCOL_*)
 *		u8	Number of addresses
 *		char[]	Name (not NUL-terminated)
 *		foreach-address {
 *			u8		Family (DNS_ADDRESS_IS_*)
 *			union {
 *				u8[4]	ipv4_addr
 *				u8[16]	ipv6_addr
 *			}
 *		}
 *	}
 *
 */
static int
dns_resolver_preparse(struct key_preparsed_payload *prep)
{
	const struct dns_server_list_v1_header *v1;
	const struct dns_payload_header *bin;
	struct user_key_payload *upayload;
	unsigned long derrno;
	int ret;
	int datalen = prep->datalen, result_len = 0;
	const char *data = prep->data, *end, *opt;

	if (datalen <= 1 || !data)
		return -EINVAL;

	if (data[0] == 0) {
		/* It may be a server list. */
		if (datalen <= sizeof(*bin))
			return -EINVAL;

		bin = (const struct dns_payload_header *)data;
		kenter("[%u,%u],%u", bin->content, bin->version, datalen);
		if (bin->content != DNS_PAYLOAD_IS_SERVER_LIST) {
			pr_warn_ratelimited(
				"dns_resolver: Unsupported content type (%u)\n",
				bin->content);
			return -EINVAL;
		}

		if (bin->version != 1) {
			pr_warn_ratelimited(
				"dns_resolver: Unsupported server list version (%u)\n",
				bin->version);
			return -EINVAL;
		}

		v1 = (const struct dns_server_list_v1_header *)bin;
		if ((v1->status != DNS_LOOKUP_GOOD &&
		     v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
			if (prep->expiry == TIME64_MAX)
				prep->expiry = ktime_get_real_seconds() + 1;
		}

		result_len = datalen;
		goto store_result;
	}

	kenter("'%*.*s',%u", datalen, datalen, data, datalen);

	if (!data || data[datalen - 1] != '\0')
		return -EINVAL;
	datalen--;

	/* deal with any options embedded in the data */
	end = data + datalen;
	opt = memchr(data, '#', datalen);
	if (!opt) {
		/* no options: the entire data is the result */
		kdebug("no options");
		result_len = datalen;
	} else {
		const char *next_opt;

		result_len = opt - data;
		opt++;
		kdebug("options: '%s'", opt);
		do {
			int opt_len, opt_nlen;
			const char *eq;
			char optval[128];

			next_opt = memchr(opt, '#', end - opt) ?: end;
			opt_len = next_opt - opt;
			if (opt_len <= 0 || opt_len > sizeof(optval)) {
				pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
						    opt_len);
				return -EINVAL;
			}

			eq = memchr(opt, '=', opt_len);
			if (eq) {
				opt_nlen = eq - opt;
				eq++;
				memcpy(optval, eq, next_opt - eq);
				optval[next_opt - eq] = '\0';
			} else {
				opt_nlen = opt_len;
				optval[0] = '\0';
			}

			kdebug("option '%*.*s' val '%s'",
			       opt_nlen, opt_nlen, opt, optval);

			/* see if it's an error number representing a DNS error
			 * that's to be recorded as the result in this key */
			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
				kdebug("dns error number option");

				ret = kstrtoul(optval, 10, &derrno);
				if (ret < 0)
					goto bad_option_value;

				if (derrno < 1 || derrno > 511)
					goto bad_option_value;

				kdebug("dns error no. = %lu", derrno);
				prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
				continue;
			}

		bad_option_value:
			pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
					    opt_nlen, opt_nlen, opt);
			return -EINVAL;
		} while (opt = next_opt + 1, opt < end);
	}

	/* don't cache the result if we're caching an error saying there's no
	 * result */
	if (prep->payload.data[dns_key_error]) {
		kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
		return 0;
	}

store_result:
	kdebug("store result");
	prep->quotalen = result_len;

	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
	if (!upayload) {
		kleave(" = -ENOMEM");
		return -ENOMEM;
	}

	upayload->datalen = result_len;
	memcpy(upayload->data, data, result_len);
	upayload->data[result_len] = '\0';

	prep->payload.data[dns_key_data] = upayload;
	kleave(" = 0");
	return 0;
}

/*
 * Clean up the preparse data
 */
static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
{
	pr_devel("==>%s()\n", __func__);

	kfree(prep->payload.data[dns_key_data]);
}

/*
 * The description is of the form "[<type>:]<domain_name>"
 *
 * The domain name may be a simple name or an absolute domain name (which
 * should end with a period).  The domain name is case-independent.
 */
static bool dns_resolver_cmp(const struct key *key,
			     const struct key_match_data *match_data)
{
	int slen, dlen, ret = 0;
	const char *src = key->description, *dsp = match_data->raw_data;

	kenter("%s,%s", src, dsp);

	if (!src || !dsp)
		goto no_match;

	if (strcasecmp(src, dsp) == 0)
		goto matched;

	slen = strlen(src);
	dlen = strlen(dsp);
	if (slen <= 0 || dlen <= 0)
		goto no_match;
	if (src[slen - 1] == '.')
		slen--;
	if (dsp[dlen - 1] == '.')
		dlen--;
	if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
		goto no_match;

matched:
	ret = 1;
no_match:
	kleave(" = %d", ret);
	return ret;
}

/*
 * Preparse the match criterion.
 */
static int dns_resolver_match_preparse(struct key_match_data *match_data)
{
	match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
	match_data->cmp = dns_resolver_cmp;
	return 0;
}

/*
 * Describe a DNS key
 */
static void dns_resolver_describe(const struct key *key, struct seq_file *m)
{
	seq_puts(m, key->description);
	if (key_is_positive(key)) {
		int err = PTR_ERR(key->payload.data[dns_key_error]);

		if (err)
			seq_printf(m, ": %d", err);
		else
			seq_printf(m, ": %u", key->datalen);
	}
}

/*
 * read the DNS data
 * - the key's semaphore is read-locked
 */
static long dns_resolver_read(const struct key *key,
			      char *buffer, size_t buflen)
{
	int err = PTR_ERR(key->payload.data[dns_key_error]);

	if (err)
		return err;

	return user_read(key, buffer, buflen);
}

struct key_type key_type_dns_resolver = {
	.name		= "dns_resolver",
	.flags		= KEY_TYPE_NET_DOMAIN | KEY_TYPE_INSTANT_REAP,
	.preparse	= dns_resolver_preparse,
	.free_preparse	= dns_resolver_free_preparse,
	.instantiate	= generic_key_instantiate,
	.match_preparse	= dns_resolver_match_preparse,
	.revoke		= user_revoke,
	.destroy	= user_destroy,
	.describe	= dns_resolver_describe,
	.read		= dns_resolver_read,
};

static int __init init_dns_resolver(void)
{
	struct cred *cred;
	struct key *keyring;
	int ret;

	/* create an override credential set with a special thread keyring in
	 * which DNS requests are cached
	 *
	 * this is used to prevent malicious redirections from being installed
	 * with add_key().
	 */
	cred = prepare_kernel_cred(&init_task);
	if (!cred)
		return -ENOMEM;

	keyring = keyring_alloc(".dns_resolver",
				GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
				(KEY_POS_ALL & ~KEY_POS_SETATTR) |
				KEY_USR_VIEW | KEY_USR_READ,
				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
	if (IS_ERR(keyring)) {
		ret = PTR_ERR(keyring);
		goto failed_put_cred;
	}

	ret = register_key_type(&key_type_dns_resolver);
	if (ret < 0)
		goto failed_put_key;

	/* instruct request_key() to use this special keyring as a cache for
	 * the results it looks up */
	set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
	cred->thread_keyring = keyring;
	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
	dns_resolver_cache = cred;

	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
	return 0;

failed_put_key:
	key_put(keyring);
failed_put_cred:
	put_cred(cred);
	return ret;
}

static void __exit exit_dns_resolver(void)
{
	key_revoke(dns_resolver_cache->thread_keyring);
	unregister_key_type(&key_type_dns_resolver);
	put_cred(dns_resolver_cache);
}

module_init(init_dns_resolver)
module_exit(exit_dns_resolver)
MODULE_LICENSE("GPL");
Commit	Line	Data
1a4240f4 WL	1	/* Key type used to cache DNS lookups made by the kernel
1a4240f4 WL	2	*
9dfe1361	3	* See Documentation/networking/dns_resolver.rst
1a4240f4 WL	4	*
	5	* Copyright (c) 2007 Igor Mammedov
	6	* Author(s): Igor Mammedov (niallain@gmail.com)
	7	* Steve French (sfrench@us.ibm.com)
	8	* Wang Lei (wang840925@gmail.com)
	9	* David Howells (dhowells@redhat.com)
	10	*
	11	* This library is free software; you can redistribute it and/or modify
	12	* it under the terms of the GNU Lesser General Public License as published
	13	* by the Free Software Foundation; either version 2.1 of the License, or
	14	* (at your option) any later version.
	15	*
	16	* This library is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
	19	* the GNU Lesser General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU Lesser General Public License
c057b190	22	* along with this library; if not, see <http://www.gnu.org/licenses/>.
1a4240f4 WL	23	*/
	24	#include <linux/module.h>
	25	#include <linux/moduleparam.h>
	26	#include <linux/slab.h>
	27	#include <linux/string.h>
	28	#include <linux/kernel.h>
	29	#include <linux/keyctl.h>
af352fe9	30	#include <linux/err.h>
4a2d7892	31	#include <linux/seq_file.h>
bbb4c432	32	#include <linux/dns_resolver.h>
1a4240f4 WL	33	#include <keys/dns_resolver-type.h>
	34	#include <keys/user-type.h>
	35	#include "internal.h"
	36
	37	MODULE_DESCRIPTION("DNS Resolver");
	38	MODULE_AUTHOR("Wang Lei");
	39	MODULE_LICENSE("GPL");
	40
95c96174	41	unsigned int dns_resolver_debug;
d6444062	42	module_param_named(debug, dns_resolver_debug, uint, 0644);
1a4240f4 WL	43	MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
	44
	45	const struct cred *dns_resolver_cache;
	46
4a2d7892 WL	47	#define DNS_ERRORNO_OPTION "dnserror"
4a2d7892 WL	48
1a4240f4	49	/*
d46d4942	50	* Preparse instantiation data for a dns_resolver key.
1a4240f4	51	*
bbb4c432 DH	52	* For normal hostname lookups, the data must be a NUL-terminated string, with
bbb4c432 DH	53	* the NUL char accounted in datalen.
1a4240f4 WL	54	*
	55	* If the data contains a '#' characters, then we take the clause after each
	56	* one to be an option of the form 'key=value'. The actual data of interest is
	57	* the string leading up to the first '#'. For instance:
	58	*
	59	* "ip1,ip2,...#foo=bar"
bbb4c432 DH	60	*
	61	* For server list requests, the data must begin with a NUL char and be
	62	* followed by a byte indicating the version of the data format. Version 1
	63	* looks something like (note this is packed):
	64	*
	65	* u8 Non-string marker (ie. 0)
	66	* u8 Content (DNS_PAYLOAD_IS_*)
	67	* u8 Version (e.g. 1)
	68	* u8 Source of server list
	69	* u8 Lookup status of server list
	70	* u8 Number of servers
	71	* foreach-server {
	72	* __le16 Name length
	73	* __le16 Priority (as per SRV record, low first)
	74	* __le16 Weight (as per SRV record, higher first)
	75	* __le16 Port
	76	* u8 Source of address list
	77	* u8 Lookup status of address list
	78	* u8 Protocol (DNS_SERVER_PROTOCOL_*)
	79	* u8 Number of addresses
	80	* char[] Name (not NUL-terminated)
	81	* foreach-address {
	82	* u8 Family (DNS_ADDRESS_IS_*)
	83	* union {
	84	* u8[4] ipv4_addr
	85	* u8[16] ipv6_addr
	86	* }
	87	* }
	88	* }
	89	*
1a4240f4 WL	90	*/
1a4240f4 WL	91	static int
d46d4942	92	dns_resolver_preparse(struct key_preparsed_payload *prep)
1a4240f4	93	{
39299bdd	94	const struct dns_server_list_v1_header *v1;
bbb4c432	95	const struct dns_payload_header *bin;
1a4240f4	96	struct user_key_payload *upayload;
4a2d7892	97	unsigned long derrno;
1a4240f4	98	int ret;
d46d4942	99	int datalen = prep->datalen, result_len = 0;
cf7f601c	100	const char data = prep->data, end, *opt;
1a4240f4	101
bbb4c432 DH	102	if (datalen <= 1 \|\| !data)
	103	return -EINVAL;
	104
	105	if (data[0] == 0) {
	106	/* It may be a server list. */
	107	if (datalen <= sizeof(*bin))
	108	return -EINVAL;
	109
	110	bin = (const struct dns_payload_header *)data;
	111	kenter("[%u,%u],%u", bin->content, bin->version, datalen);
	112	if (bin->content != DNS_PAYLOAD_IS_SERVER_LIST) {
	113	pr_warn_ratelimited(
	114	"dns_resolver: Unsupported content type (%u)\n",
	115	bin->content);
	116	return -EINVAL;
	117	}
	118
	119	if (bin->version != 1) {
	120	pr_warn_ratelimited(
	121	"dns_resolver: Unsupported server list version (%u)\n",
	122	bin->version);
	123	return -EINVAL;
	124	}
	125
39299bdd DH	126	v1 = (const struct dns_server_list_v1_header *)bin;
	127	if ((v1->status != DNS_LOOKUP_GOOD &&
	128	v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
	129	if (prep->expiry == TIME64_MAX)
	130	prep->expiry = ktime_get_real_seconds() + 1;
	131	}
	132
bbb4c432 DH	133	result_len = datalen;
	134	goto store_result;
	135	}
	136
d46d4942	137	kenter("'%.s',%u", datalen, datalen, data, datalen);
1a4240f4	138
bbb4c432	139	if (!data \|\| data[datalen - 1] != '\0')
1a4240f4 WL	140	return -EINVAL;
	141	datalen--;
	142
	143	/* deal with any options embedded in the data */
4a2d7892	144	end = data + datalen;
1a4240f4 WL	145	opt = memchr(data, '#', datalen);
1a4240f4 WL	146	if (!opt) {
4a2d7892 WL	147	/* no options: the entire data is the result */
	148	kdebug("no options");
	149	result_len = datalen;
	150	} else {
	151	const char *next_opt;
	152
	153	result_len = opt - data;
	154	opt++;
	155	kdebug("options: '%s'", opt);
	156	do {
c604cb76	157	int opt_len, opt_nlen;
4a2d7892	158	const char *eq;
c604cb76	159	char optval[128];
4a2d7892 WL	160
	161	next_opt = memchr(opt, '#', end - opt) ?: end;
	162	opt_len = next_opt - opt;
c604cb76	163	if (opt_len <= 0 \|\| opt_len > sizeof(optval)) {
9c438d7a EB	164	pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
9c438d7a EB	165	opt_len);
4a2d7892 WL	166	return -EINVAL;
	167	}
	168
c604cb76 EB	169	eq = memchr(opt, '=', opt_len);
	170	if (eq) {
	171	opt_nlen = eq - opt;
	172	eq++;
	173	memcpy(optval, eq, next_opt - eq);
	174	optval[next_opt - eq] = '\0';
	175	} else {
	176	opt_nlen = opt_len;
	177	optval[0] = '\0';
	178	}
4a2d7892	179
c604cb76 EB	180	kdebug("option '%.s' val '%s'",
c604cb76 EB	181	opt_nlen, opt_nlen, opt, optval);
4a2d7892 WL	182
	183	/* see if it's an error number representing a DNS error
	184	* that's to be recorded as the result in this key */
	185	if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
	186	memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
	187	kdebug("dns error number option");
4a2d7892	188
c604cb76	189	ret = kstrtoul(optval, 10, &derrno);
4a2d7892 WL	190	if (ret < 0)
	191	goto bad_option_value;
	192
	193	if (derrno < 1 \|\| derrno > 511)
	194	goto bad_option_value;
	195
	196	kdebug("dns error no. = %lu", derrno);
146aa8b1	197	prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
4a2d7892 WL	198	continue;
	199	}
	200
	201	bad_option_value:
9c438d7a EB	202	pr_warn_ratelimited("Option '%.s' to dns_resolver key: bad/missing value\n",
9c438d7a EB	203	opt_nlen, opt_nlen, opt);
4a2d7892 WL	204	return -EINVAL;
4a2d7892 WL	205	} while (opt = next_opt + 1, opt < end);
1a4240f4 WL	206	}
1a4240f4 WL	207
4a2d7892 WL	208	/* don't cache the result if we're caching an error saying there's no
4a2d7892 WL	209	* result */
146aa8b1 DH	210	if (prep->payload.data[dns_key_error]) {
146aa8b1 DH	211	kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
4a2d7892 WL	212	return 0;
	213	}
	214
bbb4c432	215	store_result:
4a2d7892	216	kdebug("store result");
d46d4942	217	prep->quotalen = result_len;
1a4240f4 WL	218
	219	upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
	220	if (!upayload) {
	221	kleave(" = -ENOMEM");
	222	return -ENOMEM;
	223	}
	224
	225	upayload->datalen = result_len;
	226	memcpy(upayload->data, data, result_len);
	227	upayload->data[result_len] = '\0';
1a4240f4	228
146aa8b1	229	prep->payload.data[dns_key_data] = upayload;
1a4240f4 WL	230	kleave(" = 0");
	231	return 0;
	232	}
	233
d46d4942 DH	234	/*
	235	* Clean up the preparse data
	236	*/
	237	static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
	238	{
	239	pr_devel("==>%s()\n", __func__);
	240
146aa8b1	241	kfree(prep->payload.data[dns_key_data]);
d46d4942 DH	242	}
d46d4942 DH	243
1a4240f4 WL	244	/*
	245	* The description is of the form "[<type>:]<domain_name>"
	246	*
	247	* The domain name may be a simple name or an absolute domain name (which
	248	* should end with a period). The domain name is case-independent.
	249	*/
0c903ab6 DH	250	static bool dns_resolver_cmp(const struct key *key,
0c903ab6 DH	251	const struct key_match_data *match_data)
1a4240f4 WL	252	{
1a4240f4 WL	253	int slen, dlen, ret = 0;
46291959	254	const char src = key->description, dsp = match_data->raw_data;
1a4240f4 WL	255
	256	kenter("%s,%s", src, dsp);
	257
	258	if (!src \|\| !dsp)
	259	goto no_match;
	260
	261	if (strcasecmp(src, dsp) == 0)
	262	goto matched;
	263
	264	slen = strlen(src);
	265	dlen = strlen(dsp);
	266	if (slen <= 0 \|\| dlen <= 0)
	267	goto no_match;
	268	if (src[slen - 1] == '.')
	269	slen--;
	270	if (dsp[dlen - 1] == '.')
	271	dlen--;
	272	if (slen != dlen \|\| strncasecmp(src, dsp, slen) != 0)
	273	goto no_match;
	274
	275	matched:
	276	ret = 1;
	277	no_match:
	278	kleave(" = %d", ret);
	279	return ret;
	280	}
	281
c06cfb08 DH	282	/*
	283	* Preparse the match criterion.
	284	*/
	285	static int dns_resolver_match_preparse(struct key_match_data *match_data)
	286	{
	287	match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
	288	match_data->cmp = dns_resolver_cmp;
	289	return 0;
	290	}
	291
4a2d7892 WL	292	/*
	293	* Describe a DNS key
	294	*/
	295	static void dns_resolver_describe(const struct key key, struct seq_file m)
	296	{
4a2d7892	297	seq_puts(m, key->description);
363b02da	298	if (key_is_positive(key)) {
146aa8b1 DH	299	int err = PTR_ERR(key->payload.data[dns_key_error]);
146aa8b1 DH	300
78b7280c DH	301	if (err)
	302	seq_printf(m, ": %d", err);
	303	else
	304	seq_printf(m, ": %u", key->datalen);
	305	}
4a2d7892 WL	306	}
4a2d7892 WL	307
1362fa07 DH	308	/*
	309	* read the DNS data
	310	* - the key's semaphore is read-locked
	311	*/
	312	static long dns_resolver_read(const struct key *key,
d3ec10aa	313	char *buffer, size_t buflen)
1362fa07	314	{
146aa8b1 DH	315	int err = PTR_ERR(key->payload.data[dns_key_error]);
	316
	317	if (err)
	318	return err;
1362fa07 DH	319
	320	return user_read(key, buffer, buflen);
	321	}
	322
1a4240f4 WL	323	struct key_type key_type_dns_resolver = {
1a4240f4 WL	324	.name = "dns_resolver",
39299bdd	325	.flags = KEY_TYPE_NET_DOMAIN \| KEY_TYPE_INSTANT_REAP,
d46d4942 DH	326	.preparse = dns_resolver_preparse,
	327	.free_preparse = dns_resolver_free_preparse,
	328	.instantiate = generic_key_instantiate,
c06cfb08	329	.match_preparse = dns_resolver_match_preparse,
1a4240f4 WL	330	.revoke = user_revoke,
1a4240f4 WL	331	.destroy = user_destroy,
4a2d7892	332	.describe = dns_resolver_describe,
1362fa07	333	.read = dns_resolver_read,
1a4240f4 WL	334	};
	335
	336	static int __init init_dns_resolver(void)
	337	{
	338	struct cred *cred;
	339	struct key *keyring;
	340	int ret;
	341
1a4240f4 WL	342	/* create an override credential set with a special thread keyring in
	343	* which DNS requests are cached
	344	*
	345	* this is used to prevent malicious redirections from being installed
	346	* with add_key().
	347	*/
5a17f040	348	cred = prepare_kernel_cred(&init_task);
1a4240f4 WL	349	if (!cred)
	350	return -ENOMEM;
	351
2a74dbb9 LT	352	keyring = keyring_alloc(".dns_resolver",
2a74dbb9 LT	353	GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
028db3e2 LT	354	(KEY_POS_ALL & ~KEY_POS_SETATTR) \|
028db3e2 LT	355	KEY_USR_VIEW \| KEY_USR_READ,
5ac7eace	356	KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
1a4240f4 WL	357	if (IS_ERR(keyring)) {
	358	ret = PTR_ERR(keyring);
	359	goto failed_put_cred;
	360	}
	361
1a4240f4 WL	362	ret = register_key_type(&key_type_dns_resolver);
	363	if (ret < 0)
	364	goto failed_put_key;
	365
	366	/* instruct request_key() to use this special keyring as a cache for
	367	* the results it looks up */
700920eb	368	set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
1a4240f4 WL	369	cred->thread_keyring = keyring;
	370	cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
	371	dns_resolver_cache = cred;
	372
	373	kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
	374	return 0;
	375
	376	failed_put_key:
	377	key_put(keyring);
	378	failed_put_cred:
	379	put_cred(cred);
	380	return ret;
	381	}
	382
	383	static void __exit exit_dns_resolver(void)
	384	{
	385	key_revoke(dns_resolver_cache->thread_keyring);
	386	unregister_key_type(&key_type_dns_resolver);
	387	put_cred(dns_resolver_cache);
1a4240f4 WL	388	}
	389
	390	module_init(init_dns_resolver)
	391	module_exit(exit_dns_resolver)
	392	MODULE_LICENSE("GPL");