167 lines
4.6 KiB
C
167 lines
4.6 KiB
C
/* Upcall routine, designed to work as a key type and working through
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* /sbin/request-key to contact userspace when handling DNS queries.
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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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* The upcall wrapper used to make an arbitrary DNS query.
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*
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* This function requires the appropriate userspace tool dns.upcall to be
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* installed and something like the following lines should be added to the
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* /etc/request-key.conf file:
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*
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* create dns_resolver * * /sbin/dns.upcall %k
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*
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* For example to use this module to query AFSDB RR:
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*
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* create dns_resolver afsdb:* * /sbin/dns.afsdb %k
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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/slab.h>
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#include <linux/dns_resolver.h>
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#include <linux/err.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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/**
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* dns_query - Query the DNS
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* @type: Query type (or NULL for straight host->IP lookup)
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* @name: Name to look up
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* @namelen: Length of name
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* @options: Request options (or NULL if no options)
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* @_result: Where to place the returned data.
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* @_expiry: Where to store the result expiry time (or NULL)
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*
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* The data will be returned in the pointer at *result, and the caller is
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* responsible for freeing it.
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*
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* The description should be of the form "[<query_type>:]<domain_name>", and
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* the options need to be appropriate for the query type requested. If no
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* query_type is given, then the query is a straight hostname to IP address
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* lookup.
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*
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* The DNS resolution lookup is performed by upcalling to userspace by way of
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* requesting a key of type dns_resolver.
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*
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* Returns the size of the result on success, -ve error code otherwise.
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*/
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int dns_query(const char *type, const char *name, size_t namelen,
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const char *options, char **_result, time_t *_expiry)
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{
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struct key *rkey;
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struct user_key_payload *upayload;
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const struct cred *saved_cred;
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size_t typelen, desclen;
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char *desc, *cp;
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int ret, len;
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kenter("%s,%*.*s,%zu,%s",
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type, (int)namelen, (int)namelen, name, namelen, options);
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if (!name || namelen == 0 || !_result)
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return -EINVAL;
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/* construct the query key description as "[<type>:]<name>" */
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typelen = 0;
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desclen = 0;
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if (type) {
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typelen = strlen(type);
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if (typelen < 1)
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return -EINVAL;
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desclen += typelen + 1;
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}
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if (!namelen)
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namelen = strnlen(name, 256);
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if (namelen < 3 || namelen > 255)
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return -EINVAL;
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desclen += namelen + 1;
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desc = kmalloc(desclen, GFP_KERNEL);
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if (!desc)
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return -ENOMEM;
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cp = desc;
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if (type) {
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memcpy(cp, type, typelen);
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cp += typelen;
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*cp++ = ':';
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}
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memcpy(cp, name, namelen);
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cp += namelen;
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*cp = '\0';
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if (!options)
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options = "";
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kdebug("call request_key(,%s,%s)", desc, options);
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/* make the upcall, using special credentials to prevent the use of
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* add_key() to preinstall malicious redirections
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*/
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saved_cred = override_creds(dns_resolver_cache);
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rkey = request_key(&key_type_dns_resolver, desc, options);
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revert_creds(saved_cred);
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kfree(desc);
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if (IS_ERR(rkey)) {
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ret = PTR_ERR(rkey);
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goto out;
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}
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down_read(&rkey->sem);
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set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
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rkey->perm |= KEY_USR_VIEW;
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ret = key_validate(rkey);
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if (ret < 0)
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goto put;
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/* If the DNS server gave an error, return that to the caller */
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ret = rkey->type_data.x[0];
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if (ret)
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goto put;
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upayload = rcu_dereference_protected(rkey->payload.data,
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lockdep_is_held(&rkey->sem));
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len = upayload->datalen;
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ret = -ENOMEM;
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*_result = kmalloc(len + 1, GFP_KERNEL);
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if (!*_result)
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goto put;
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memcpy(*_result, upayload->data, len);
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(*_result)[len] = '\0';
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if (_expiry)
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*_expiry = rkey->expiry;
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ret = len;
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put:
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up_read(&rkey->sem);
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key_put(rkey);
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out:
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kleave(" = %d", ret);
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return ret;
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}
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EXPORT_SYMBOL(dns_query);
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