1 files changed, 159 insertions, 0 deletions
diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
new file mode 100644
index 000000000000..6c0cf31ea00d
--- /dev/null
+++ b/net/dns_resolver/dns_query.c
@@ -0,0 +1,159 @@
+/* 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 <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;
+
+	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);