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384 lines
9.7 KiB
384 lines
9.7 KiB
/* Key type used to cache DNS lookups made by the kernel |
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* |
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* See Documentation/networking/dns_resolver.rst |
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* |
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* Copyright (c) 2007 Igor Mammedov |
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* Author(s): Igor Mammedov ([email protected]) |
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* Steve French ([email protected]) |
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* Wang Lei ([email protected]) |
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* David Howells ([email protected]) |
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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 *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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