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![Wang Lei](/assets/img/avatar_default.png)
If the DNS server returns an error, allow that to be cached in the DNS resolver key in lieu of a value. Userspace passes the desired error number as an option in the payload: "#dnserror=<number>" Userspace must map h_errno from the name resolution routines to an appropriate Linux error before passing it up. Something like the following mapping is recommended: [HOST_NOT_FOUND] = ENODATA, [TRY_AGAIN] = EAGAIN, [NO_RECOVERY] = ECONNREFUSED, [NO_DATA] = ENODATA, in lieu of Linux errors specifically for representing name service errors. The filesystem must map these errors appropropriately before passing them to userspace. AFS is made to map ENODATA and EAGAIN to EDESTADDRREQ for the return to userspace; ECONNREFUSED is allowed to stand as is. The error can be seen in /proc/keys as a negative number after the description of the key. Compare, for example, the following key entries: 2f97238c I--Q-- 1 53s 3f010000 0 0 dns_resol afsdb:grand.centrall.org: -61 338bfbbe I--Q-- 1 59m 3f010000 0 0 dns_resol afsdb:grand.central.org: 37 If the error option is supplied in the payload, the main part of the payload is discarded. The key should have an expiry time set by userspace. Signed-off-by: Wang Lei <wang840925@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: Steve French <sfrench@us.ibm.com>
293 lines
7.6 KiB
C
293 lines
7.6 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, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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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 <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 dns_resolver_debug;
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module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
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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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* Instantiate a user defined key for dns_resolver.
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*
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* The data must be a NUL-terminated string, with the NUL char accounted in
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* 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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static int
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dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
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{
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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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size_t result_len = 0;
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const char *data = _data, *end, *opt;
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kenter("%%%d,%s,'%s',%zu",
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key->serial, key->description, data, datalen);
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if (datalen <= 1 || !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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const char *eq;
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int opt_len, opt_nlen, opt_vlen, tmp;
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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) {
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printk(KERN_WARNING
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"Empty option to dns_resolver key %d\n",
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key->serial);
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return -EINVAL;
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}
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eq = memchr(opt, '=', opt_len) ?: end;
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opt_nlen = eq - opt;
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eq++;
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opt_vlen = next_opt - eq; /* will be -1 if no value */
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tmp = opt_vlen >= 0 ? opt_vlen : 0;
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kdebug("option '%*.*s' val '%*.*s'",
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opt_nlen, opt_nlen, opt, tmp, tmp, eq);
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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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if (opt_vlen <= 0)
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goto bad_option_value;
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ret = strict_strtoul(eq, 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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key->type_data.x[0] = -derrno;
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continue;
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}
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bad_option_value:
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printk(KERN_WARNING
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"Option '%*.*s' to dns_resolver key %d:"
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" bad/missing value\n",
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opt_nlen, opt_nlen, opt, key->serial);
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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 (key->type_data.x[0]) {
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kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
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return 0;
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}
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kdebug("store result");
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ret = key_payload_reserve(key, result_len);
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if (ret < 0)
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return -EINVAL;
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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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rcu_assign_pointer(key->payload.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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* 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 int
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dns_resolver_match(const struct key *key, const void *description)
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{
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int slen, dlen, ret = 0;
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const char *src = key->description, *dsp = description;
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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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* 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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int err = key->type_data.x[0];
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seq_puts(m, key->description);
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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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struct key_type key_type_dns_resolver = {
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.name = "dns_resolver",
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.instantiate = dns_resolver_instantiate,
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.match = dns_resolver_match,
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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 = user_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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printk(KERN_NOTICE "Registering the %s key type\n",
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key_type_dns_resolver.name);
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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 = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, 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);
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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 = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
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if (ret < 0)
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goto failed_put_key;
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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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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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printk(KERN_NOTICE "Unregistered %s key type\n",
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key_type_dns_resolver.name);
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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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