| /* Upcall routine, designed to work as a key type and working through |
| * /sbin/request-key to contact userspace when handling DNS queries. |
| * |
| * See Documentation/networking/dns_resolver.txt |
| * |
| * Copyright (c) 2007 Igor Mammedov |
| * Author(s): Igor Mammedov (niallain@gmail.com) |
| * Steve French (sfrench@us.ibm.com) |
| * Wang Lei (wang840925@gmail.com) |
| * David Howells (dhowells@redhat.com) |
| * |
| * The upcall wrapper used to make an arbitrary DNS query. |
| * |
| * This function requires the appropriate userspace tool dns.upcall to be |
| * installed and something like the following lines should be added to the |
| * /etc/request-key.conf file: |
| * |
| * create dns_resolver * * /sbin/dns.upcall %k |
| * |
| * For example to use this module to query AFSDB RR: |
| * |
| * create dns_resolver afsdb:* * /sbin/dns.afsdb %k |
| * |
| * This library is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU Lesser General Public License as published |
| * by the Free Software Foundation; either version 2.1 of the License, or |
| * (at your option) any later version. |
| * |
| * This library is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See |
| * the GNU Lesser General Public License for more details. |
| * |
| * You should have received a copy of the GNU Lesser General Public License |
| * along with this library; if not, see <http://www.gnu.org/licenses/>. |
| */ |
| |
| #include <linux/module.h> |
| #include <linux/slab.h> |
| #include <linux/cred.h> |
| #include <linux/dns_resolver.h> |
| #include <linux/err.h> |
| |
| #include <keys/dns_resolver-type.h> |
| #include <keys/user-type.h> |
| |
| #include "internal.h" |
| |
| /** |
| * dns_query - Query the DNS |
| * @type: Query type (or NULL for straight host->IP lookup) |
| * @name: Name to look up |
| * @namelen: Length of name |
| * @options: Request options (or NULL if no options) |
| * @_result: Where to place the returned data (or NULL) |
| * @_expiry: Where to store the result expiry time (or NULL) |
| * @invalidate: Always invalidate the key after use |
| * |
| * The data will be returned in the pointer at *result, if provided, and the |
| * caller is responsible for freeing it. |
| * |
| * The description should be of the form "[<query_type>:]<domain_name>", and |
| * the options need to be appropriate for the query type requested. If no |
| * query_type is given, then the query is a straight hostname to IP address |
| * lookup. |
| * |
| * The DNS resolution lookup is performed by upcalling to userspace by way of |
| * requesting a key of type dns_resolver. |
| * |
| * Returns the size of the result on success, -ve error code otherwise. |
| */ |
| int dns_query(const char *type, const char *name, size_t namelen, |
| const char *options, char **_result, time64_t *_expiry, |
| bool invalidate) |
| { |
| struct key *rkey; |
| struct user_key_payload *upayload; |
| const struct cred *saved_cred; |
| size_t typelen, desclen; |
| char *desc, *cp; |
| int ret, len; |
| |
| kenter("%s,%*.*s,%zu,%s", |
| type, (int)namelen, (int)namelen, name, namelen, options); |
| |
| if (!name || namelen == 0) |
| return -EINVAL; |
| |
| /* construct the query key description as "[<type>:]<name>" */ |
| typelen = 0; |
| desclen = 0; |
| if (type) { |
| typelen = strlen(type); |
| if (typelen < 1) |
| return -EINVAL; |
| desclen += typelen + 1; |
| } |
| |
| if (namelen < 3 || namelen > 255) |
| return -EINVAL; |
| desclen += namelen + 1; |
| |
| desc = kmalloc(desclen, GFP_KERNEL); |
| if (!desc) |
| return -ENOMEM; |
| |
| cp = desc; |
| if (type) { |
| memcpy(cp, type, typelen); |
| cp += typelen; |
| *cp++ = ':'; |
| } |
| memcpy(cp, name, namelen); |
| cp += namelen; |
| *cp = '\0'; |
| |
| if (!options) |
| options = ""; |
| kdebug("call request_key(,%s,%s)", desc, options); |
| |
| /* make the upcall, using special credentials to prevent the use of |
| * add_key() to preinstall malicious redirections |
| */ |
| saved_cred = override_creds(dns_resolver_cache); |
| rkey = request_key(&key_type_dns_resolver, desc, options); |
| revert_creds(saved_cred); |
| kfree(desc); |
| if (IS_ERR(rkey)) { |
| ret = PTR_ERR(rkey); |
| goto out; |
| } |
| |
| down_read(&rkey->sem); |
| set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags); |
| rkey->perm |= KEY_USR_VIEW; |
| |
| ret = key_validate(rkey); |
| if (ret < 0) |
| goto put; |
| |
| /* If the DNS server gave an error, return that to the caller */ |
| ret = PTR_ERR(rkey->payload.data[dns_key_error]); |
| if (ret) |
| goto put; |
| |
| upayload = user_key_payload_locked(rkey); |
| len = upayload->datalen; |
| |
| if (_result) { |
| ret = -ENOMEM; |
| *_result = kmemdup_nul(upayload->data, len, GFP_KERNEL); |
| if (!*_result) |
| goto put; |
| } |
| |
| if (_expiry) |
| *_expiry = rkey->expiry; |
| |
| ret = len; |
| put: |
| up_read(&rkey->sem); |
| if (invalidate) |
| key_invalidate(rkey); |
| key_put(rkey); |
| out: |
| kleave(" = %d", ret); |
| return ret; |
| } |
| EXPORT_SYMBOL(dns_query); |