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Diffstat (limited to 'net/dns_resolver/dns_query.c')
| -rw-r--r-- | net/dns_resolver/dns_query.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c new file mode 100644 index 00000000..c32be292 --- /dev/null +++ b/net/dns_resolver/dns_query.c @@ -0,0 +1,165 @@ +/* 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, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include <linux/module.h> +#include <linux/slab.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. + * @_expiry: Where to store the result expiry time (or NULL) + * + * The data will be returned in the pointer at *result, 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, time_t *_expiry) +{ + 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 || !_result) + 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) + namelen = strlen(name); + if (namelen < 3) + 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); + 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 = rkey->type_data.x[0]; + if (ret) + goto put; + + upayload = rcu_dereference_protected(rkey->payload.data, + lockdep_is_held(&rkey->sem)); + len = upayload->datalen; + + ret = -ENOMEM; + *_result = kmalloc(len + 1, GFP_KERNEL); + if (!*_result) + goto put; + + memcpy(*_result, upayload->data, len + 1); + if (_expiry) + *_expiry = rkey->expiry; + + ret = len; +put: + up_read(&rkey->sem); + key_put(rkey); +out: + kleave(" = %d", ret); + return ret; +} +EXPORT_SYMBOL(dns_query); |