385 lines
9.7 KiB
C
385 lines
9.7 KiB
C
/* Key type used to cache DNS lookups made by the kernel
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*
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* See Documentation/networking/dns_resolver.txt
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*
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* Copyright (c) 2007 Igor Mammedov
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* Author(s): Igor Mammedov (niallain@gmail.com)
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* Steve French (sfrench@us.ibm.com)
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* Wang Lei (wang840925@gmail.com)
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* David Howells (dhowells@redhat.com)
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <linux/module.h>
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#include <linux/moduleparam.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/kernel.h>
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#include <linux/keyctl.h>
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#include <linux/err.h>
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#include <linux/seq_file.h>
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#include <linux/dns_resolver.h>
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#include <keys/dns_resolver-type.h>
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#include <keys/user-type.h>
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#include "internal.h"
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MODULE_DESCRIPTION("DNS Resolver");
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MODULE_AUTHOR("Wang Lei");
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MODULE_LICENSE("GPL");
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unsigned int dns_resolver_debug;
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module_param_named(debug, dns_resolver_debug, uint, 0644);
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MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
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const struct cred *dns_resolver_cache;
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#define DNS_ERRORNO_OPTION "dnserror"
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/*
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* Preparse instantiation data for a dns_resolver key.
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*
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* For normal hostname lookups, the data must be a NUL-terminated string, with
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* the NUL char accounted in datalen.
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*
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* If the data contains a '#' characters, then we take the clause after each
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* one to be an option of the form 'key=value'. The actual data of interest is
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* the string leading up to the first '#'. For instance:
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*
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* "ip1,ip2,...#foo=bar"
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*
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* For server list requests, the data must begin with a NUL char and be
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* followed by a byte indicating the version of the data format. Version 1
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* looks something like (note this is packed):
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*
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* u8 Non-string marker (ie. 0)
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* u8 Content (DNS_PAYLOAD_IS_*)
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* u8 Version (e.g. 1)
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* u8 Source of server list
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* u8 Lookup status of server list
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* u8 Number of servers
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* foreach-server {
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* __le16 Name length
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* __le16 Priority (as per SRV record, low first)
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* __le16 Weight (as per SRV record, higher first)
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* __le16 Port
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* u8 Source of address list
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* u8 Lookup status of address list
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* u8 Protocol (DNS_SERVER_PROTOCOL_*)
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* u8 Number of addresses
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* char[] Name (not NUL-terminated)
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* foreach-address {
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* u8 Family (DNS_ADDRESS_IS_*)
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* union {
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* u8[4] ipv4_addr
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* u8[16] ipv6_addr
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* }
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* }
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* }
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*
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*/
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static int
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dns_resolver_preparse(struct key_preparsed_payload *prep)
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{
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const struct dns_payload_header *bin;
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struct user_key_payload *upayload;
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unsigned long derrno;
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int ret;
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int datalen = prep->datalen, result_len = 0;
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const char *data = prep->data, *end, *opt;
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if (datalen <= 1 || !data)
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return -EINVAL;
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if (data[0] == 0) {
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/* It may be a server list. */
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if (datalen <= sizeof(*bin))
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return -EINVAL;
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bin = (const struct dns_payload_header *)data;
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kenter("[%u,%u],%u", bin->content, bin->version, datalen);
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if (bin->content != DNS_PAYLOAD_IS_SERVER_LIST) {
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pr_warn_ratelimited(
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"dns_resolver: Unsupported content type (%u)\n",
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bin->content);
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return -EINVAL;
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}
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if (bin->version != 1) {
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pr_warn_ratelimited(
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"dns_resolver: Unsupported server list version (%u)\n",
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bin->version);
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return -EINVAL;
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}
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result_len = datalen;
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goto store_result;
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}
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kenter("'%*.*s',%u", datalen, datalen, data, datalen);
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if (!data || data[datalen - 1] != '\0')
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return -EINVAL;
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datalen--;
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/* deal with any options embedded in the data */
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end = data + datalen;
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opt = memchr(data, '#', datalen);
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if (!opt) {
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/* no options: the entire data is the result */
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kdebug("no options");
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result_len = datalen;
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} else {
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const char *next_opt;
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result_len = opt - data;
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opt++;
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kdebug("options: '%s'", opt);
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do {
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int opt_len, opt_nlen;
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const char *eq;
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char optval[128];
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next_opt = memchr(opt, '#', end - opt) ?: end;
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opt_len = next_opt - opt;
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if (opt_len <= 0 || opt_len > sizeof(optval)) {
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pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
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opt_len);
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return -EINVAL;
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}
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eq = memchr(opt, '=', opt_len);
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if (eq) {
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opt_nlen = eq - opt;
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eq++;
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memcpy(optval, eq, next_opt - eq);
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optval[next_opt - eq] = '\0';
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} else {
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opt_nlen = opt_len;
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optval[0] = '\0';
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}
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kdebug("option '%*.*s' val '%s'",
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opt_nlen, opt_nlen, opt, optval);
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/* see if it's an error number representing a DNS error
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* that's to be recorded as the result in this key */
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if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
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memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
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kdebug("dns error number option");
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ret = kstrtoul(optval, 10, &derrno);
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if (ret < 0)
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goto bad_option_value;
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if (derrno < 1 || derrno > 511)
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goto bad_option_value;
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kdebug("dns error no. = %lu", derrno);
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prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
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continue;
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}
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bad_option_value:
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pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n",
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opt_nlen, opt_nlen, opt);
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return -EINVAL;
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} while (opt = next_opt + 1, opt < end);
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}
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/* don't cache the result if we're caching an error saying there's no
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* result */
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if (prep->payload.data[dns_key_error]) {
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kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
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return 0;
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}
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store_result:
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kdebug("store result");
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prep->quotalen = result_len;
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upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
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if (!upayload) {
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kleave(" = -ENOMEM");
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return -ENOMEM;
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}
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upayload->datalen = result_len;
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memcpy(upayload->data, data, result_len);
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upayload->data[result_len] = '\0';
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prep->payload.data[dns_key_data] = upayload;
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kleave(" = 0");
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return 0;
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}
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/*
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* Clean up the preparse data
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*/
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static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
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{
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pr_devel("==>%s()\n", __func__);
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kfree(prep->payload.data[dns_key_data]);
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}
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/*
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* The description is of the form "[<type>:]<domain_name>"
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*
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* The domain name may be a simple name or an absolute domain name (which
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* should end with a period). The domain name is case-independent.
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*/
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static bool dns_resolver_cmp(const struct key *key,
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const struct key_match_data *match_data)
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{
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int slen, dlen, ret = 0;
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const char *src = key->description, *dsp = match_data->raw_data;
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kenter("%s,%s", src, dsp);
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if (!src || !dsp)
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goto no_match;
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if (strcasecmp(src, dsp) == 0)
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goto matched;
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slen = strlen(src);
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dlen = strlen(dsp);
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if (slen <= 0 || dlen <= 0)
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goto no_match;
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if (src[slen - 1] == '.')
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slen--;
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if (dsp[dlen - 1] == '.')
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dlen--;
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if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
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goto no_match;
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matched:
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ret = 1;
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no_match:
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kleave(" = %d", ret);
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return ret;
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}
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/*
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* Preparse the match criterion.
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*/
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static int dns_resolver_match_preparse(struct key_match_data *match_data)
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{
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match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
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match_data->cmp = dns_resolver_cmp;
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return 0;
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}
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/*
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* Describe a DNS key
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*/
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static void dns_resolver_describe(const struct key *key, struct seq_file *m)
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{
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seq_puts(m, key->description);
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if (key_is_positive(key)) {
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int err = PTR_ERR(key->payload.data[dns_key_error]);
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if (err)
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seq_printf(m, ": %d", err);
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else
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seq_printf(m, ": %u", key->datalen);
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}
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}
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/*
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* read the DNS data
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* - the key's semaphore is read-locked
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*/
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static long dns_resolver_read(const struct key *key,
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char __user *buffer, size_t buflen)
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{
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int err = PTR_ERR(key->payload.data[dns_key_error]);
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if (err)
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return err;
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return user_read(key, buffer, buflen);
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}
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struct key_type key_type_dns_resolver = {
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.name = "dns_resolver",
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.flags = KEY_TYPE_NET_DOMAIN,
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.preparse = dns_resolver_preparse,
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.free_preparse = dns_resolver_free_preparse,
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.instantiate = generic_key_instantiate,
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.match_preparse = dns_resolver_match_preparse,
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.revoke = user_revoke,
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.destroy = user_destroy,
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.describe = dns_resolver_describe,
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.read = dns_resolver_read,
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};
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static int __init init_dns_resolver(void)
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{
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struct cred *cred;
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struct key *keyring;
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int ret;
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/* create an override credential set with a special thread keyring in
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* which DNS requests are cached
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*
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* this is used to prevent malicious redirections from being installed
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* with add_key().
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*/
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cred = prepare_kernel_cred(NULL);
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if (!cred)
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return -ENOMEM;
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keyring = keyring_alloc(".dns_resolver",
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GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
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(KEY_POS_ALL & ~KEY_POS_SETATTR) |
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KEY_USR_VIEW | KEY_USR_READ,
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KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
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if (IS_ERR(keyring)) {
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ret = PTR_ERR(keyring);
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goto failed_put_cred;
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}
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ret = register_key_type(&key_type_dns_resolver);
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if (ret < 0)
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goto failed_put_key;
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/* instruct request_key() to use this special keyring as a cache for
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* the results it looks up */
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set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
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cred->thread_keyring = keyring;
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cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
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dns_resolver_cache = cred;
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kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
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return 0;
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failed_put_key:
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key_put(keyring);
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failed_put_cred:
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put_cred(cred);
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return ret;
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}
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static void __exit exit_dns_resolver(void)
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{
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key_revoke(dns_resolver_cache->thread_keyring);
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unregister_key_type(&key_type_dns_resolver);
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put_cred(dns_resolver_cache);
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}
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module_init(init_dns_resolver)
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module_exit(exit_dns_resolver)
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MODULE_LICENSE("GPL");
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