![David Howells](/assets/img/avatar_default.png)
The kernel contains some special internal keyrings, for instance the DNS resolver keyring : 2a93faf1 I----- 1 perm 1f030000 0 0 keyring .dns_resolver: empty It would occasionally be useful to allow the contents of such keyrings to be flushed by root (cache invalidation). Allow a flag to be set on a keyring to mark that someone possessing the sysadmin capability can clear the keyring, even without normal write access to the keyring. Set this flag on the special keyrings created by the DNS resolver, the NFS identity mapper and the CIFS identity mapper. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Jeff Layton <jlayton@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Signed-off-by: James Morris <jmorris@namei.org>
311 lines
8 KiB
C
311 lines
8 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,
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(int)datalen, (int)datalen, 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 (key_is_instantiated(key)) {
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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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if (key->type_data.x[0])
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return key->type_data.x[0];
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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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.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 = 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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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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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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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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