/* 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 ([email protected])
* Steve French ([email protected])
* Wang Lei ([email protected])
* David Howells ([email protected])
*
* 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)
{
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) {
const struct dns_server_list_v1_header *v1;
/* It may be a server list. */
if (datalen < sizeof(*v1))
return -EINVAL;
v1 = (const struct dns_server_list_v1_header *)data;
kenter("[%u,%u],%u", v1->hdr.content, v1->hdr.version, datalen);
if (v1->hdr.content != DNS_PAYLOAD_IS_SERVER_LIST) {
pr_warn_ratelimited(
"dns_resolver: Unsupported content type (%u)\n",
v1->hdr.content);
return -EINVAL;
}
if (v1->hdr.version != 1) {
pr_warn_ratelimited(
"dns_resolver: Unsupported server list version (%u)\n",
v1->hdr.version);
return -EINVAL;
}
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");
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