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bbb4c4323a
Allow the DNS resolver to retrieve a set of servers and their associated addresses, ports, preference and weight ratings. In terms of communication with userspace, "srv=1" is added to the callout string (the '1' indicating the maximum data version supported by the kernel) to ask the userspace side for this. If the userspace side doesn't recognise it, it will ignore the option and return the usual text address list. If the userspace side does recognise it, it will return some binary data that begins with a zero byte that would cause the string parsers to give an error. The second byte contains the version of the data in the blob (this may be between 1 and the version specified in the callout data). The remainder of the payload is version-specific. In version 1, the payload looks like (note that this is packed): u8 Non-string marker (ie. 0) u8 Content (0 => Server list) u8 Version (ie. 1) u8 Source (eg. DNS_RECORD_FROM_DNS_SRV) u8 Status (eg. DNS_LOOKUP_GOOD) u8 Number of servers foreach-server { u16 Name length (LE) u16 Priority (as per SRV record) (LE) u16 Weight (as per SRV record) (LE) u16 Port (LE) u8 Source (eg. DNS_RECORD_FROM_NSS) u8 Status (eg. DNS_LOOKUP_GOT_NOT_FOUND) u8 Protocol (eg. DNS_SERVER_PROTOCOL_UDP) u8 Number of addresses char[] Name (not NUL-terminated) foreach-address { u8 Family (AF_INET{,6}) union { u8[4] ipv4_addr u8[16] ipv6_addr } } } This can then be used to fetch a whole cell's VL-server configuration for AFS, for example. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
384 lines
9.7 KiB
C
384 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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.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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