14 files changed, 708 insertions, 205 deletions

diff --git a/Documentation/networking/dns_resolver.txt b/Documentation/networking/dns_resolver.txt
new file mode 100644
index 00000000000..d8e0ce1d38c
--- /dev/null
+++ b/Documentation/networking/dns_resolver.txt
@@ -0,0 +1,146 @@
+                             ===================
+                             DNS Resolver Module
+                             ===================
+
+Contents:
+
+ - Overview.
+ - Compilation.
+ - Setting up.
+ - Usage.
+ - Mechanism.
+ - Debugging.
+
+
+========
+OVERVIEW
+========
+
+The DNS resolver module provides a way for kernel services to make DNS queries
+by way of requesting a key of key type dns_resolver.  These queries are
+upcalled to userspace through /sbin/request-key.
+
+These routines must be supported by userspace tools dns.upcall, cifs.upcall and
+request-key.  It is under development and does not yet provide the full feature
+set.  The features it does support include:
+
+ (*) Implements the dns_resolver key_type to contact userspace.
+
+It does not yet support the following AFS features:
+
+ (*) Dns query support for AFSDB resource record.
+
+This code is extracted from the CIFS filesystem.
+
+
+===========
+COMPILATION
+===========
+
+The module should be enabled by turning on the kernel configuration options:
+
+        CONFIG_DNS_RESOLVER     - tristate "DNS Resolver support"
+
+
+==========
+SETTING UP
+==========
+
+To set up this facility, the /etc/request-key.conf file must be altered so that
+/sbin/request-key can appropriately direct the upcalls.  For example, to handle
+basic dname to IPv4/IPv6 address resolution, the following line should be
+added:
+
+        #OP     TYPE            DESC    CO-INFO PROGRAM ARG1 ARG2 ARG3 ...
+        #====== ============    ======= ======= ==========================
+        create  dns_resolver    *       *       /usr/sbin/cifs.upcall %k
+
+To direct a query for query type 'foo', a line of the following should be added
+before the more general line given above as the first match is the one taken.
+
+        create  dns_resolver    foo:*   *       /usr/sbin/dns.foo %k
+
+
+
+=====
+USAGE
+=====
+
+To make use of this facility, one of the following functions that are
+implemented in the module can be called after doing:
+
+        #include <linux/dns_resolver.h>
+
+ (1) int dns_query(const char *type, const char *name, size_t namelen,
+                   const char *options, char **_result, time_t *_expiry);
+
+     This is the basic access function.  It looks for a cached DNS query and if
+     it doesn't find it, it upcalls to userspace to make a new DNS query, which
+     may then be cached.  The key description is constructed as a string of the
+     form:
+
+                [<type>:]<name>
+
+     where <type> optionally specifies the particular upcall program to invoke,
+     and thus the type of query to do, and <name> specifies the string to be
+     looked up.  The default query type is a straight hostname to IP address
+     set lookup.
+
+     The name parameter is not required to be a NUL-terminated string, and its
+     length should be given by the namelen argument.
+
+     The options parameter may be NULL or it may be a set of options
+     appropriate to the query type.
+
+     The return value is a string appropriate to the query type.  For instance,
+     for the default query type it is just a list of comma-separated IPv4 and
+     IPv6 addresses.  The caller must free the result.
+
+     The length of the result string is returned on success, and a -ve error
+     code is returned otherwise.  -EKEYREJECTED will be returned if the DNS
+     lookup failed.
+
+     If _expiry is non-NULL, the expiry time (TTL) of the result will be
+     returned also.
+
+
+=========
+MECHANISM
+=========
+
+The dnsresolver module registers a key type called "dns_resolver".  Keys of
+this type are used to transport and cache DNS lookup results from userspace.
+
+When dns_query() is invoked, it calls request_key() to search the local
+keyrings for a cached DNS result.  If that fails to find one, it upcalls to
+userspace to get a new result.
+
+Upcalls to userspace are made through the request_key() upcall vector, and are
+directed by means of configuration lines in /etc/request-key.conf that tell
+/sbin/request-key what program to run to instantiate the key.
+
+The upcall handler program is responsible for querying the DNS, processing the
+result into a form suitable for passing to the keyctl_instantiate_key()
+routine.  This then passes the data to dns_resolver_instantiate() which strips
+off and processes any options included in the data, and then attaches the
+remainder of the string to the key as its payload.
+
+The upcall handler program should set the expiry time on the key to that of the
+lowest TTL of all the records it has extracted a result from.  This means that
+the key will be discarded and recreated when the data it holds has expired.
+
+dns_query() returns a copy of the value attached to the key, or an error if
+that is indicated instead.
+
+See <file:Documentation/keys-request-key.txt> for further information about
+request-key function.
+
+
+=========
+DEBUGGING
+=========
+
+Debugging messages can be turned on dynamically by writing a 1 into the
+following file:
+
+        /sys/module/dnsresolver/parameters/debug
diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
index 5739fd7f88b..57f0aa9f141 100644
--- a/fs/cifs/Kconfig
+++ b/fs/cifs/Kconfig
@@ -71,14 +71,14 @@ config CIFS_WEAK_PW_HASH
           If unsure, say N.
 
 config CIFS_UPCALL
-          bool "Kerberos/SPNEGO advanced session setup"
-          depends on CIFS && KEYS
-          help
-            Enables an upcall mechanism for CIFS which accesses
-            userspace helper utilities to provide SPNEGO packaged (RFC 4178)
-            Kerberos tickets which are needed to mount to certain secure servers
-            (for which more secure Kerberos authentication is required). If
-            unsure, say N.
+        bool "Kerberos/SPNEGO advanced session setup"
+        depends on CIFS && KEYS
+        select DNS_RESOLVER
+        help
+          Enables an upcall mechanism for CIFS which accesses userspace helper
+          utilities to provide SPNEGO packaged (RFC 4178) Kerberos tickets
+          which are needed to mount to certain secure servers (for which more
+          secure Kerberos authentication is required). If unsure, say N.
 
 config CIFS_XATTR
         bool "CIFS extended attributes"
@@ -122,6 +122,7 @@ config CIFS_DEBUG2
 config CIFS_DFS_UPCALL
           bool "DFS feature support"
           depends on CIFS && KEYS
+          select DNS_RESOLVER
           help
             Distributed File System (DFS) support is used to access shares
             transparently in an enterprise name space, even if the share
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 8a2cf129e53..2a0c892959f 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -45,7 +45,6 @@
 #include "cifs_fs_sb.h"
 #include <linux/mm.h>
 #include <linux/key-type.h>
-#include "dns_resolve.h"
 #include "cifs_spnego.h"
 #include "fscache.h"
 #define CIFS_MAGIC_NUMBER 0xFF534D42    /* the first four bytes of SMB PDUs */
@@ -934,22 +933,13 @@ init_cifs(void)
         if (rc)
                 goto out_unregister_filesystem;
 #endif
-#ifdef CONFIG_CIFS_DFS_UPCALL
-        rc = cifs_init_dns_resolver();
-        if (rc)
-                goto out_unregister_key_type;
-#endif
         rc = slow_work_register_user(THIS_MODULE);
         if (rc)
-                goto out_unregister_resolver_key;
+                goto out_unregister_key_type;
 
         return 0;
 
- out_unregister_resolver_key:
-#ifdef CONFIG_CIFS_DFS_UPCALL
-        cifs_exit_dns_resolver();
  out_unregister_key_type:
-#endif
 #ifdef CONFIG_CIFS_UPCALL
         unregister_key_type(&cifs_spnego_key_type);
  out_unregister_filesystem:
@@ -976,7 +966,6 @@ exit_cifs(void)
         cifs_fscache_unregister();
 #ifdef CONFIG_CIFS_DFS_UPCALL
         cifs_dfs_release_automount_timer();
-        cifs_exit_dns_resolver();
 #endif
 #ifdef CONFIG_CIFS_UPCALL
         unregister_key_type(&cifs_spnego_key_type);
diff --git a/fs/cifs/dns_resolve.c b/fs/cifs/dns_resolve.c
index aa967e7917f..0eb87026cad 100644
--- a/fs/cifs/dns_resolve.c
+++ b/fs/cifs/dns_resolve.c
@@ -4,6 +4,8 @@
  *   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)
  *
  *   Contains the CIFS DFS upcall routines used for hostname to
  *   IP address translation.
@@ -24,212 +26,73 @@
  */
 
 #include <linux/slab.h>
-#include <linux/keyctl.h>
-#include <linux/key-type.h>
-#include <keys/user-type.h>
+#include <linux/dns_resolver.h>
 #include "dns_resolve.h"
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "cifs_debug.h"
 
-static const struct cred *dns_resolver_cache;
-
-/* Checks if supplied name is IP address
- * returns:
- *              1 - name is IP
- *              0 - name is not IP
- */
-static int
-is_ip(const char *name, int len)
-{
-        struct sockaddr_storage ss;
-
-        return cifs_convert_address((struct sockaddr *)&ss, name, len);
-}
-
-static int
-dns_resolver_instantiate(struct key *key, const void *data,
-                size_t datalen)
-{
-        int rc = 0;
-        char *ip;
-
-        /* make sure this looks like an address */
-        if (!is_ip(data, datalen))
-                return -EINVAL;
-
-        ip = kmalloc(datalen + 1, GFP_KERNEL);
-        if (!ip)
-                return -ENOMEM;
-
-        memcpy(ip, data, datalen);
-        ip[datalen] = '\0';
-
-        key->type_data.x[0] = datalen;
-        key->payload.data = ip;
-
-        return rc;
-}
-
-static void
-dns_resolver_destroy(struct key *key)
-{
-        kfree(key->payload.data);
-}
-
-struct key_type key_type_dns_resolver = {
-        .name        = "dns_resolver",
-        .def_datalen = sizeof(struct in_addr),
-        .describe    = user_describe,
-        .instantiate = dns_resolver_instantiate,
-        .destroy     = dns_resolver_destroy,
-        .match       = user_match,
-};
-
-/* Resolves server name to ip address.
- * input:
- *      unc - server UNC
- * output:
- *      *ip_addr - pointer to server ip, caller responcible for freeing it.
- * return the length of the returned string on success
+/**
+ * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
+ * @unc: UNC path specifying the server
+ * @ip_addr: Where to return the IP address.
+ *
+ * The IP address will be returned in string form, and the caller is
+ * responsible for freeing it.
+ *
+ * Returns length of result on success, -ve on error.
  */
 int
 dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
 {
-        const struct cred *saved_cred;
-        int rc = -EAGAIN;
-        struct key *rkey = ERR_PTR(-EAGAIN);
+        struct sockaddr_storage ss;
+        const char *hostname, *sep;
         char *name;
-        char *data = NULL;
-        int len;
+        int len, rc;
 
         if (!ip_addr || !unc)
                 return -EINVAL;
 
-        /* search for server name delimiter */
         len = strlen(unc);
         if (len < 3) {
                 cFYI(1, "%s: unc is too short: %s", __func__, unc);
                 return -EINVAL;
         }
-        len -= 2;
-        name = memchr(unc+2, '\\', len);
-        if (!name) {
-                cFYI(1, "%s: probably server name is whole unc: %s",
-                                        __func__, unc);
-        } else {
-                len = (name - unc) - 2/* leading // */;
-        }
-
-        name = kmalloc(len+1, GFP_KERNEL);
-        if (!name) {
-                rc = -ENOMEM;
-                return rc;
-        }
-        memcpy(name, unc+2, len);
-        name[len] = 0;
-
-        if (is_ip(name, len)) {
-                cFYI(1, "%s: it is IP, skipping dns upcall: %s",
-                                        __func__, name);
-                data = name;
-                goto skip_upcall;
-        }
 
-        saved_cred = override_creds(dns_resolver_cache);
-        rkey = request_key(&key_type_dns_resolver, name, "");
-        revert_creds(saved_cred);
-        if (!IS_ERR(rkey)) {
-                if (!(rkey->perm & KEY_USR_VIEW)) {
-                        down_read(&rkey->sem);
-                        rkey->perm |= KEY_USR_VIEW;
-                        up_read(&rkey->sem);
-                }
-                len = rkey->type_data.x[0];
-                data = rkey->payload.data;
-        } else {
-                cERROR(1, "%s: unable to resolve: %s", __func__, name);
-                goto out;
-        }
-
-skip_upcall:
-        if (data) {
-                *ip_addr = kmalloc(len + 1, GFP_KERNEL);
-                if (*ip_addr) {
-                        memcpy(*ip_addr, data, len + 1);
-                        if (!IS_ERR(rkey))
-                                cFYI(1, "%s: resolved: %s to %s", __func__,
-                                                        name,
-                                                        *ip_addr
-                                        );
-                        rc = len;
-                } else {
-                        rc = -ENOMEM;
-                }
-                if (!IS_ERR(rkey))
-                        key_put(rkey);
-        }
+        /* Discount leading slashes for cifs */
+        len -= 2;
+        hostname = unc + 2;
 
-out:
-        kfree(name);
+        /* Search for server name delimiter */
+        sep = memchr(hostname, '\\', len);
+        if (sep)
+                len = sep - unc;
+        else
+                cFYI(1, "%s: probably server name is whole unc: %s",
+                     __func__, unc);
+
+        /* Try to interpret hostname as an IPv4 or IPv6 address */
+        rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
+        if (rc > 0)
+                goto name_is_IP_address;
+
+        /* Perform the upcall */
+        rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
+        if (rc < 0)
+                cERROR(1, "%s: unable to resolve: %*.*s",
+                       __func__, len, len, hostname);
+        else
+                cFYI(1, "%s: resolved: %*.*s to %s",
+                     __func__, len, len, hostname, *ip_addr);
         return rc;
-}
 
-int __init cifs_init_dns_resolver(void)
-{
-        struct cred *cred;
-        struct key *keyring;
-        int ret;
-
-        printk(KERN_NOTICE "Registering the %s key type\n",
-               key_type_dns_resolver.name);
-
-        /* create an override credential set with a special thread keyring in
-         * which DNS requests are cached
-         *
-         * this is used to prevent malicious redirections from being installed
-         * with add_key().
-         */
-        cred = prepare_kernel_cred(NULL);
-        if (!cred)
+name_is_IP_address:
+        name = kmalloc(len + 1, GFP_KERNEL);
+        if (!name)
                 return -ENOMEM;
-
-        keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
-                            (KEY_POS_ALL & ~KEY_POS_SETATTR) |
-                            KEY_USR_VIEW | KEY_USR_READ,
-                            KEY_ALLOC_NOT_IN_QUOTA);
-        if (IS_ERR(keyring)) {
-                ret = PTR_ERR(keyring);
-                goto failed_put_cred;
-        }
-
-        ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
-        if (ret < 0)
-                goto failed_put_key;
-
-        ret = register_key_type(&key_type_dns_resolver);
-        if (ret < 0)
-                goto failed_put_key;
-
-        /* instruct request_key() to use this special keyring as a cache for
-         * the results it looks up */
-        cred->thread_keyring = keyring;
-        cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
-        dns_resolver_cache = cred;
+        memcpy(name, hostname, len);
+        name[len] = 0;
+        cFYI(1, "%s: unc is IP, skipping dns upcall: %s", __func__, name);
+        *ip_addr = name;
         return 0;
-
-failed_put_key:
-        key_put(keyring);
-failed_put_cred:
-        put_cred(cred);
-        return ret;
-}
-
-void cifs_exit_dns_resolver(void)
-{
-        key_revoke(dns_resolver_cache->thread_keyring);
-        unregister_key_type(&key_type_dns_resolver);
-        put_cred(dns_resolver_cache);
-        printk(KERN_NOTICE "Unregistered %s key type\n",
-               key_type_dns_resolver.name);
 }
diff --git a/fs/cifs/dns_resolve.h b/fs/cifs/dns_resolve.h
index 5d7f291df16..d3f5d27f4d0 100644
--- a/fs/cifs/dns_resolve.h
+++ b/fs/cifs/dns_resolve.h
@@ -24,8 +24,6 @@
 #define _DNS_RESOLVE_H
 
 #ifdef __KERNEL__
-extern int __init cifs_init_dns_resolver(void);
-extern void cifs_exit_dns_resolver(void);
 extern int dns_resolve_server_name_to_ip(const char *unc, char **ip_addr);
 #endif /* KERNEL */
 
diff --git a/include/keys/dns_resolver-type.h b/include/keys/dns_resolver-type.h
new file mode 100644
index 00000000000..9284a19393a
--- /dev/null
+++ b/include/keys/dns_resolver-type.h
@@ -0,0 +1,23 @@
+/* DNS resolver key type
+ *
+ * Copyright (C) 2010 Wang Lei. All Rights Reserved.
+ * Written by Wang Lei (wang840925@gmail.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#ifndef _KEYS_DNS_RESOLVER_TYPE_H
+#define _KEYS_DNS_RESOLVER_TYPE_H
+
+#include <linux/key-type.h>
+
+extern struct key_type key_type_dns_resolver;
+
+extern int request_dns_resolver_key(const char *description,
+                                    const char *callout_info,
+                                    char **data);
+
+#endif /* _KEYS_DNS_RESOLVER_TYPE_H */
diff --git a/include/linux/dns_resolver.h b/include/linux/dns_resolver.h
new file mode 100644
index 00000000000..cc92268af89
--- /dev/null
+++ b/include/linux/dns_resolver.h
@@ -0,0 +1,34 @@
+/*
+ *   DNS Resolver upcall management for CIFS DFS and AFS
+ *   Handles host name to IP address resolution and DNS query for AFSDB RR.
+ *
+ *   Copyright (c) International Business Machines  Corp., 2008
+ *   Author(s): Steve French (sfrench@us.ibm.com)
+ *              Wang Lei (wang840925@gmail.com)
+ *
+ *   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
+ */
+
+#ifndef _LINUX_DNS_RESOLVER_H
+#define _LINUX_DNS_RESOLVER_H
+
+#ifdef __KERNEL__
+
+extern int dns_query(const char *type, const char *name, size_t namelen,
+                     const char *options, char **_result, time_t *_expiry);
+
+#endif /* KERNEL */
+
+#endif /* _LINUX_DNS_RESOLVER_H */
diff --git a/net/Kconfig b/net/Kconfig
index e24fa0873f3..e330594d370 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -213,6 +213,7 @@ source "net/phonet/Kconfig"
 source "net/ieee802154/Kconfig"
 source "net/sched/Kconfig"
 source "net/dcb/Kconfig"
+source "net/dns_resolver/Kconfig"
 
 config RPS
         boolean
diff --git a/net/Makefile b/net/Makefile
index 41d420070a3..ea60fbce9b1 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -67,3 +67,4 @@ ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_SYSCTL)            += sysctl_net.o
 endif
 obj-$(CONFIG_WIMAX)             += wimax/
+obj-$(CONFIG_DNS_RESOLVER)      += dns_resolver/
diff --git a/net/dns_resolver/Kconfig b/net/dns_resolver/Kconfig
new file mode 100644
index 00000000000..2ec47cb5d0d
--- /dev/null
+++ b/net/dns_resolver/Kconfig
@@ -0,0 +1,27 @@
+#
+# Configuration for DNS Resolver
+#
+config DNS_RESOLVER
+        tristate "DNS Resolver support"
+        depends on NET && KEYS
+        help
+          Saying Y here will include support for the DNS Resolver key type
+          which can be used to make upcalls to perform DNS lookups in
+          userspace.
+
+          DNS Resolver is used to query DNS server for information.  Examples
+          being resolving a UNC hostname element to an IP address for CIFS or
+          performing a DNS query for AFSDB records so that AFS can locate a
+          cell's volume location database servers.
+
+          DNS Resolver is used by the CIFS and AFS modules, and would support
+          samba4 later.  DNS Resolver is supported by the userspace upcall
+          helper "/sbin/dns.resolver" via /etc/request-key.conf.
+
+          See <file:Documentation/networking/dns_resolver.txt> for further
+          information.
+
+          To compile this as a module, choose M here: the module will be called
+          dnsresolver.
+
+          If unsure, say N.
diff --git a/net/dns_resolver/Makefile b/net/dns_resolver/Makefile
new file mode 100644
index 00000000000..c0ef4e71dc4
--- /dev/null
+++ b/net/dns_resolver/Makefile
@@ -0,0 +1,7 @@
+#
+# Makefile for the Linux DNS Resolver.
+#
+
+obj-$(CONFIG_DNS_RESOLVER) += dns_resolver.o
+
+dns_resolver-objs :=  dns_key.o dns_query.o
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
new file mode 100644
index 00000000000..1b1b411adcf
--- /dev/null
+++ b/net/dns_resolver/dns_key.c
@@ -0,0 +1,210 @@
+/* Key type used to cache DNS lookups made by the kernel
+ *
+ * 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)
+ *
+ *   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/moduleparam.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/kernel.h>
+#include <linux/keyctl.h>
+#include <keys/dns_resolver-type.h>
+#include <keys/user-type.h>
+#include "internal.h"
+
+MODULE_DESCRIPTION("DNS Resolver");
+MODULE_AUTHOR("Wang Lei");
+MODULE_LICENSE("GPL");
+
+unsigned dns_resolver_debug;
+module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
+MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
+
+const struct cred *dns_resolver_cache;
+
+/*
+ * Instantiate a user defined key for dns_resolver.
+ *
+ * The data must be a NUL-terminated string, with the NUL char accounted in
+ * datalen.
+ *
+ * If the data contains a '#' characters, then we take the clause after each
+ * one to be an option of the form 'key=value'.  The actual data of interest is
+ * the string leading up to the first '#'.  For instance:
+ *
+ *        "ip1,ip2,...#foo=bar"
+ */
+static int
+dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
+{
+        struct user_key_payload *upayload;
+        int ret;
+        size_t result_len = 0;
+        const char *data = _data, *opt;
+
+        kenter("%%%d,%s,'%s',%zu",
+               key->serial, key->description, data, datalen);
+
+        if (datalen <= 1 || !data || data[datalen - 1] != '\0')
+                return -EINVAL;
+        datalen--;
+
+        /* deal with any options embedded in the data */
+        opt = memchr(data, '#', datalen);
+        if (!opt) {
+                kdebug("no options currently supported");
+                return -EINVAL;
+        }
+
+        result_len = datalen;
+        ret = key_payload_reserve(key, result_len);
+        if (ret < 0)
+                return -EINVAL;
+
+        upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
+        if (!upayload) {
+                kleave(" = -ENOMEM");
+                return -ENOMEM;
+        }
+
+        upayload->datalen = result_len;
+        memcpy(upayload->data, data, result_len);
+        upayload->data[result_len] = '\0';
+        rcu_assign_pointer(key->payload.data, upayload);
+
+        kleave(" = 0");
+        return 0;
+}
+
+/*
+ * The description is of the form "[<type>:]<domain_name>"
+ *
+ * The domain name may be a simple name or an absolute domain name (which
+ * should end with a period).  The domain name is case-independent.
+ */
+static int
+dns_resolver_match(const struct key *key, const void *description)
+{
+        int slen, dlen, ret = 0;
+        const char *src = key->description, *dsp = description;
+
+        kenter("%s,%s", src, dsp);
+
+        if (!src || !dsp)
+                goto no_match;
+
+        if (strcasecmp(src, dsp) == 0)
+                goto matched;
+
+        slen = strlen(src);
+        dlen = strlen(dsp);
+        if (slen <= 0 || dlen <= 0)
+                goto no_match;
+        if (src[slen - 1] == '.')
+                slen--;
+        if (dsp[dlen - 1] == '.')
+                dlen--;
+        if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
+                goto no_match;
+
+matched:
+        ret = 1;
+no_match:
+        kleave(" = %d", ret);
+        return ret;
+}
+
+struct key_type key_type_dns_resolver = {
+        .name           = "dns_resolver",
+        .instantiate    = dns_resolver_instantiate,
+        .match          = dns_resolver_match,
+        .revoke         = user_revoke,
+        .destroy        = user_destroy,
+        .describe       = user_describe,
+        .read           = user_read,
+};
+
+static int __init init_dns_resolver(void)
+{
+        struct cred *cred;
+        struct key *keyring;
+        int ret;
+
+        printk(KERN_NOTICE "Registering the %s key type\n",
+               key_type_dns_resolver.name);
+
+        /* create an override credential set with a special thread keyring in
+         * which DNS requests are cached
+         *
+         * this is used to prevent malicious redirections from being installed
+         * with add_key().
+         */
+        cred = prepare_kernel_cred(NULL);
+        if (!cred)
+                return -ENOMEM;
+
+        keyring = key_alloc(&key_type_keyring, ".dns_resolver", 0, 0, cred,
+                            (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+                            KEY_USR_VIEW | KEY_USR_READ,
+                            KEY_ALLOC_NOT_IN_QUOTA);
+        if (IS_ERR(keyring)) {
+                ret = PTR_ERR(keyring);
+                goto failed_put_cred;
+        }
+
+        ret = key_instantiate_and_link(keyring, NULL, 0, NULL, NULL);
+        if (ret < 0)
+                goto failed_put_key;
+
+        ret = register_key_type(&key_type_dns_resolver);
+        if (ret < 0)
+                goto failed_put_key;
+
+        /* instruct request_key() to use this special keyring as a cache for
+         * the results it looks up */
+        cred->thread_keyring = keyring;
+        cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
+        dns_resolver_cache = cred;
+
+        kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
+        return 0;
+
+failed_put_key:
+        key_put(keyring);
+failed_put_cred:
+        put_cred(cred);
+        return ret;
+}
+
+static void __exit exit_dns_resolver(void)
+{
+        key_revoke(dns_resolver_cache->thread_keyring);
+        unregister_key_type(&key_type_dns_resolver);
+        put_cred(dns_resolver_cache);
+        printk(KERN_NOTICE "Unregistered %s key type\n",
+               key_type_dns_resolver.name);
+}
+
+module_init(init_dns_resolver)
+module_exit(exit_dns_resolver)
+MODULE_LICENSE("GPL");
diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
new file mode 100644
index 00000000000..6c0cf31ea00
--- /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);
diff --git a/net/dns_resolver/internal.h b/net/dns_resolver/internal.h
new file mode 100644
index 00000000000..189ca9e9b78
--- /dev/null
+++ b/net/dns_resolver/internal.h
@@ -0,0 +1,44 @@
+/*
+ *   Copyright (c) 2010 Wang Lei
+ *   Author(s): Wang Lei (wang840925@gmail.com). All Rights Reserved.
+ *
+ *   Internal DNS Rsolver stuff
+ *
+ *   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/compiler.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+
+/*
+ * dns_key.c
+ */
+extern const struct cred *dns_resolver_cache;
+
+/*
+ * debug tracing
+ */
+extern unsigned dns_resolver_debug;
+
+#define kdebug(FMT, ...)                                \
+do {                                                    \
+        if (unlikely(dns_resolver_debug))               \
+                printk(KERN_DEBUG "[%-6.6s] "FMT"\n",   \
+                       current->comm, ##__VA_ARGS__);   \
+} while (0)
+
+#define kenter(FMT, ...) kdebug("==> %s("FMT")", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) kdebug("<== %s()"FMT"", __func__, ##__VA_ARGS__)