[3/4] Provide generic DNS query function

Commit Message

David Howells July 7, 2010, 9:14 a.m. UTC

None

Patch

diff --git a/include/linux/dns_resolver.h b/include/linux/dns_resolver.h
index 72b9edf..328cc05 100644
--- a/include/linux/dns_resolver.h
+++ b/include/linux/dns_resolver.h
@@ -29,6 +29,8 @@ 
 extern int request_dns_resolution(const char *description, const char *options,
 				  char **result);
 extern int dns_resolve_unc_to_ip(const char *unc, char **ip_addr);
+extern int dns_query(const char *type, const char *name, const char *inetf,
+		     char **_result, time_t *_expiry);
 
 #endif /* KERNEL */
 
diff --git a/net/dnsresolver/Makefile b/net/dnsresolver/Makefile
index 260ccc4..aa7e422 100644
--- a/net/dnsresolver/Makefile
+++ b/net/dnsresolver/Makefile
@@ -4,4 +4,4 @@ 
 
 obj-$(CONFIG_DNS_RESOLVER) += dnsresolver.o
 
-dnsresolver-objs :=  dns_resolver.o resolv_unc_to_ip.o
+dnsresolver-objs :=  dns_resolver.o resolv_unc_to_ip.o dns_query.o
diff --git a/net/dnsresolver/dns_query.c b/net/dnsresolver/dns_query.c
new file mode 100644
index 0000000..61ef026
--- /dev/null
+++ b/net/dnsresolver/dns_query.c
@@ -0,0 +1,130 @@ 
+/*
+ *   Copyright (c) 2010 Wang Lei
+ *   Author(s): Wang Lei ([e-mail])
+ *		David Howells <[e-mail]>
+ *
+ *   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/dnsresolver-type.h>
+#include <keys/user-type.h>
+
+#include "internal.h"
+
+/**
+ * dns_query - Query DNS
+ * @type: Query type
+ * @name: Name to look up
+ * @options: Space-separated options appropriate to the query type
+ * @_result: Where to return the result
+ * @_expiry: Where to store the result expiry time (or NULL)
+ *
+ * The result is copied into a buffer and returned in *_result.  The caller is
+ * responsible for freeing this buffer.  The result is NUL-terminated, though
+ * the termination is not included in the result size.  Optionally, the time at
+ * which the result expires is stored in *_expiry.
+ *
+ * Note that the upcall program may have edited the result from what the DNS
+ * server returned, for example to turn hostnames obtained by the lookup into
+ * IP addresses for the AFSDB query type.
+ *
+ * The options may include such things as IP address family ("ipv4" or "ipv6")
+ *
+ * Returns the size of the result on success, -ve error code otherwise.
+ */
+int dns_query(const char *type, const char *name, const char *options,
+	      char **_result, time_t *_expiry)
+{
+	struct key *rkey;
+	size_t typelen, namelen;
+	struct user_key_payload *upayload;
+	char *desc;
+	int ret, len;
+
+	kenter("%s,%s,%s,,,", type, name, options);
+
+	ret =  -EINVAL;
+	if (!type || !name || !_result)
+		goto err;
+
+	typelen = strlen(type);
+	namelen = strlen(name);
+	if (typelen < 1 || namelen < 3)
+		goto err;
+
+	ret = -ENOMEM;
+	/* construct the query key description as "<type>:<name>" */
+	desc = kmalloc(typelen + 1 + namelen + 1, GFP_KERNEL);
+	if (!desc)
+		goto err;
+
+	memcpy(desc, type, typelen);
+	desc[typelen] = ':';
+	memcpy(desc + typelen + 1, name, namelen + 1);
+
+	if (!options)
+		options = "";
+	kdebug("call request_key(,%s,%s)", desc, options);
+
+	/* make the upcall */
+	rkey = request_key(&key_type_dns_resolver, desc, options);
+	kfree(desc);
+
+	if (IS_ERR(rkey)) {
+		ret = PTR_ERR(rkey);
+		goto err;
+	}
+
+	down_read(&rkey->sem);
+
+	upayload = rcu_dereference_check(rkey->payload.data,
+					 lockdep_is_held(&rkey->sem));
+	len = upayload->datalen;
+	*_result = kmalloc(len + 1, GFP_KERNEL);
+	if (!*_result) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	memcpy(*_result, upayload->data, len + 1);
+	if (_expiry)
+		*_expiry = rkey->expiry;
+	ret = len;
+
+
+out:
+	up_read(&rkey->sem);
+	key_put(rkey);
+
+err:
+	kleave(" = %d [r=%s]", ret, *_result);
+	return ret;
+}
+EXPORT_SYMBOL(dns_query);