Merge git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6

* git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6:
  [DNS RESOLVER] Minor typo correction
  DNS: Fixes for the DNS query module
  cifs: Include linux/err.h for IS_ERR and PTR_ERR
  DNS: Make AFS go to the DNS for AFSDB records for unknown cells
  DNS: Separate out CIFS DNS Resolver code
  cifs: account for new creduid=0x%x parameter in spnego upcall string
  cifs: reduce false positives with inode aliasing serverino autodisable
  CIFS: Make cifs_convert_address() take a const src pointer and a length
  cifs: show features compiled in as part of DebugData
  cifs: update README

Fix up trivial conflicts in fs/cifs/cifsfs.c due to workqueue changes

24 files changed, 833 insertions, 257 deletions

diff --git a/Documentation/networking/dns_resolver.txt b/Documentation/networking/dns_resolver.txt
new file mode 100644
index 00000000000..aefd1e68180
--- /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 negative
+     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/afs/Kconfig b/fs/afs/Kconfig
index 5c4e61d3c77..8f975f25b48 100644
--- a/fs/afs/Kconfig
+++ b/fs/afs/Kconfig
@@ -2,6 +2,7 @@ config AFS_FS
 	tristate "Andrew File System support (AFS) (EXPERIMENTAL)"
 	depends on INET && EXPERIMENTAL
 	select AF_RXRPC
+	select DNS_RESOLVER
 	help
 	  If you say Y here, you will get an experimental Andrew File System
 	  driver. It currently only supports unsecured read-only AFS access.
diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index e19c13f059e..ffea35c6387 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/key.h>
 #include <linux/ctype.h>
+#include <linux/dns_resolver.h>
 #include <linux/sched.h>
 #include <keys/rxrpc-type.h>
 #include "internal.h"
@@ -36,6 +37,8 @@ static struct afs_cell *afs_cell_alloc(const char *name, char *vllist)
 	struct key *key;
 	size_t namelen;
 	char keyname[4 + AFS_MAXCELLNAME + 1], *cp, *dp, *next;
+	char  *dvllist = NULL, *_vllist = NULL;
+	char  delimiter = ':';
 	int ret;
 
 	_enter("%s,%s", name, vllist);
@@ -43,8 +46,10 @@ static struct afs_cell *afs_cell_alloc(const char *name, char *vllist)
 	BUG_ON(!name); /* TODO: want to look up "this cell" in the cache */
 
 	namelen = strlen(name);
-	if (namelen > AFS_MAXCELLNAME)
+	if (namelen > AFS_MAXCELLNAME) {
+		_leave(" = -ENAMETOOLONG");
 		return ERR_PTR(-ENAMETOOLONG);
+	}
 
 	/* allocate and initialise a cell record */
 	cell = kzalloc(sizeof(struct afs_cell) + namelen + 1, GFP_KERNEL);
@@ -64,15 +69,31 @@ static struct afs_cell *afs_cell_alloc(const char *name, char *vllist)
 	INIT_LIST_HEAD(&cell->vl_list);
 	spin_lock_init(&cell->vl_lock);
 
+	/* if the ip address is invalid, try dns query */
+	if (!vllist || strlen(vllist) < 7) {
+		ret = dns_query("afsdb", name, namelen, "ipv4", &dvllist, NULL);
+		if (ret < 0) {
+			_leave(" = %d", ret);
+			return ERR_PTR(ret);
+		}
+		_vllist = dvllist;
+
+		/* change the delimiter for user-space reply */
+		delimiter = ',';
+
+	} else {
+		_vllist = vllist;
+	}
+
 	/* fill in the VL server list from the rest of the string */
 	do {
 		unsigned a, b, c, d;
 
-		next = strchr(vllist, ':');
+		next = strchr(_vllist, delimiter);
 		if (next)
 			*next++ = 0;
 
-		if (sscanf(vllist, "%u.%u.%u.%u", &a, &b, &c, &d) != 4)
+		if (sscanf(_vllist, "%u.%u.%u.%u", &a, &b, &c, &d) != 4)
 			goto bad_address;
 
 		if (a > 255 || b > 255 || c > 255 || d > 255)
@@ -81,7 +102,7 @@ static struct afs_cell *afs_cell_alloc(const char *name, char *vllist)
 		cell->vl_addrs[cell->vl_naddrs++].s_addr =
 			htonl((a << 24) | (b << 16) | (c << 8) | d);
 
-	} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS && (vllist = next));
+	} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS && (_vllist = next));
 
 	/* create a key to represent an anonymous user */
 	memcpy(keyname, "afs@", 4);
@@ -110,6 +131,7 @@ bad_address:
 	ret = -EINVAL;
 error:
 	key_put(cell->anonymous_key);
+	kfree(dvllist);
 	kfree(cell);
 	_leave(" = %d", ret);
 	return ERR_PTR(ret);
@@ -201,14 +223,12 @@ int afs_cell_init(char *rootcell)
 	}
 
 	cp = strchr(rootcell, ':');
-	if (!cp) {
-		printk(KERN_ERR "kAFS: no VL server IP addresses specified\n");
-		_leave(" = -EINVAL");
-		return -EINVAL;
-	}
+	if (!cp)
+		_debug("kAFS: no VL server IP addresses specified");
+	else
+		*cp++ = 0;
 
 	/* allocate a cell record for the root cell */
-	*cp++ = 0;
 	new_root = afs_cell_create(rootcell, cp);
 	if (IS_ERR(new_root)) {
 		_leave(" = %ld", PTR_ERR(new_root));
diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
index efcb3a78a32..917b7d449bb 100644
--- a/fs/cifs/Kconfig
+++ b/fs/cifs/Kconfig
@@ -70,14 +70,14 @@ 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"
@@ -121,6 +121,7 @@ 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/README b/fs/cifs/README
index a727b7cb075..a7081eeeb85 100644
--- a/fs/cifs/README
+++ b/fs/cifs/README
@@ -568,8 +568,9 @@ module can be displayed via modinfo.
 Misc /proc/fs/cifs Flags and Debug Info
 =======================================
 Informational pseudo-files:
-DebugData		Displays information about active CIFS sessions
-			and shares, as well as the cifs.ko version.
+DebugData		Displays information about active CIFS sessions and
+			shares, features enabled as well as the cifs.ko
+			version.
 Stats			Lists summary resource usage information as well as per
 			share statistics, if CONFIG_CIFS_STATS in enabled
 			in the kernel configuration.
diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index 4fce6e61b34..eb1ba493489 100644
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -119,6 +119,31 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 		    "Display Internal CIFS Data Structures for Debugging\n"
 		    "---------------------------------------------------\n");
 	seq_printf(m, "CIFS Version %s\n", CIFS_VERSION);
+	seq_printf(m, "Features: ");
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	seq_printf(m, "dfs");
+	seq_putc(m, ' ');
+#endif
+#ifdef CONFIG_CIFS_FSCACHE
+	seq_printf(m, "fscache");
+	seq_putc(m, ' ');
+#endif
+#ifdef CONFIG_CIFS_WEAK_PW_HASH
+	seq_printf(m, "lanman");
+	seq_putc(m, ' ');
+#endif
+#ifdef CONFIG_CIFS_POSIX
+	seq_printf(m, "posix");
+	seq_putc(m, ' ');
+#endif
+#ifdef CONFIG_CIFS_UPCALL
+	seq_printf(m, "spnego");
+	seq_putc(m, ' ');
+#endif
+#ifdef CONFIG_CIFS_XATTR
+	seq_printf(m, "xattr");
+#endif
+	seq_putc(m, '\n');
 	seq_printf(m, "Active VFS Requests: %d\n", GlobalTotalActiveXid);
 	seq_printf(m, "Servers:");
 
diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c
index dc1ed50ea06..d6ced7aa23c 100644
--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -141,7 +141,7 @@ char *cifs_compose_mount_options(const char *sb_mountdata,
 	}
 
 	rc = dns_resolve_server_name_to_ip(*devname, &srvIP);
-	if (rc != 0) {
+	if (rc < 0) {
 		cERROR(1, "%s: Failed to resolve server part of %s to IP: %d",
 			  __func__, *devname, rc);
 		goto compose_mount_options_err;
@@ -150,8 +150,7 @@ char *cifs_compose_mount_options(const char *sb_mountdata,
 	 * assuming that we have 'unc=' and 'ip=' in
 	 * the original sb_mountdata
 	 */
-	md_len = strlen(sb_mountdata) + strlen(srvIP) +
-		strlen(ref->node_name) + 12;
+	md_len = strlen(sb_mountdata) + rc + strlen(ref->node_name) + 12;
 	mountdata = kzalloc(md_len+1, GFP_KERNEL);
 	if (mountdata == NULL) {
 		rc = -ENOMEM;
diff --git a/fs/cifs/cifs_spnego.c b/fs/cifs/cifs_spnego.c
index 6effccff85a..87044906cd1 100644
--- a/fs/cifs/cifs_spnego.c
+++ b/fs/cifs/cifs_spnego.c
@@ -84,6 +84,9 @@ struct key_type cifs_spnego_key_type = {
 /* strlen of ";uid=0x" */
 #define UID_KEY_LEN		7
 
+/* strlen of ";creduid=0x" */
+#define CREDUID_KEY_LEN		11
+
 /* strlen of ";user=" */
 #define USER_KEY_LEN		6
 
@@ -107,6 +110,7 @@ cifs_get_spnego_key(struct cifsSesInfo *sesInfo)
 		   IP_KEY_LEN + INET6_ADDRSTRLEN +
 		   MAX_MECH_STR_LEN +
 		   UID_KEY_LEN + (sizeof(uid_t) * 2) +
+		   CREDUID_KEY_LEN + (sizeof(uid_t) * 2) +
 		   USER_KEY_LEN + strlen(sesInfo->userName) +
 		   PID_KEY_LEN + (sizeof(pid_t) * 2) + 1;
 
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 5ac541a30c1..a5ed10c9afe 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
 
 	return 0;
 
-#ifdef CONFIG_CIFS_DFS_UPCALL
- out_unregister_key_type:
-#endif
 #ifdef CONFIG_CIFS_UPCALL
-	unregister_key_type(&cifs_spnego_key_type);
  out_unregister_filesystem:
-#endif
 	unregister_filesystem(&cifs_fs_type);
+#endif
  out_destroy_request_bufs:
 	cifs_destroy_request_bufs();
  out_destroy_mids:
@@ -971,7 +961,6 @@ 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/cifsproto.h b/fs/cifs/cifsproto.h
index 2eaebbd3113..1f545081408 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -86,8 +86,8 @@ extern unsigned int smbCalcSize(struct smb_hdr *ptr);
 extern unsigned int smbCalcSize_LE(struct smb_hdr *ptr);
 extern int decode_negTokenInit(unsigned char *security_blob, int length,
 			struct TCP_Server_Info *server);
-extern int cifs_convert_address(struct sockaddr *dst, char *src);
-extern int cifs_fill_sockaddr(struct sockaddr *dst, char *src,
+extern int cifs_convert_address(struct sockaddr *dst, const char *src, int len);
+extern int cifs_fill_sockaddr(struct sockaddr *dst, const char *src, int len,
 				unsigned short int port);
 extern int map_smb_to_linux_error(struct smb_hdr *smb, int logErr);
 extern void header_assemble(struct smb_hdr *, char /* command */ ,
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 2a43a0aca96..95c2ea67edf 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1543,6 +1543,7 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
 	if (volume_info->UNCip && volume_info->UNC) {
 		rc = cifs_fill_sockaddr((struct sockaddr *)&addr,
 					volume_info->UNCip,
+					strlen(volume_info->UNCip),
 					volume_info->port);
 		if (!rc) {
 			/* we failed translating address */
diff --git a/fs/cifs/dns_resolve.c b/fs/cifs/dns_resolve.c
index 3ad7f4300c4..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.
@@ -24,214 +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(char *name)
-{
-	struct sockaddr_storage ss;
-
-	return cifs_convert_address((struct sockaddr *)&ss, name);
-}
-
-static int
-dns_resolver_instantiate(struct key *key, const void *data,
-		size_t datalen)
-{
-	int rc = 0;
-	char *ip;
-
-	ip = kmalloc(datalen + 1, GFP_KERNEL);
-	if (!ip)
-		return -ENOMEM;
-
-	memcpy(ip, data, datalen);
-	ip[datalen] = '\0';
-
-	/* make sure this looks like an address */
-	if (!is_ip(ip)) {
-		kfree(ip);
-		return -EINVAL;
-	}
-
-	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 0 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)) {
-		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 = 0;
-		} 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/fs/cifs/inode.c b/fs/cifs/inode.c
index a15b3a9bbff..dc4c47ab958 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -732,15 +732,9 @@ cifs_find_inode(struct inode *inode, void *opaque)
 	if ((inode->i_mode & S_IFMT) != (fattr->cf_mode & S_IFMT))
 		return 0;
 
-	/*
-	 * uh oh -- it's a directory. We can't use it since hardlinked dirs are
-	 * verboten. Disable serverino and return it as if it were found, the
-	 * caller can discard it, generate a uniqueid and retry the find
-	 */
-	if (S_ISDIR(inode->i_mode) && !list_empty(&inode->i_dentry)) {
+	/* if it's not a directory or has no dentries, then flag it */
+	if (S_ISDIR(inode->i_mode) && !list_empty(&inode->i_dentry))
 		fattr->cf_flags |= CIFS_FATTR_INO_COLLISION;
-		cifs_autodisable_serverino(CIFS_SB(inode->i_sb));
-	}
 
 	return 1;
 }
@@ -754,6 +748,27 @@ cifs_init_inode(struct inode *inode, void *opaque)
 	return 0;
 }
 
+/*
+ * walk dentry list for an inode and report whether it has aliases that
+ * are hashed. We use this to determine if a directory inode can actually
+ * be used.
+ */
+static bool
+inode_has_hashed_dentries(struct inode *inode)
+{
+	struct dentry *dentry;
+
+	spin_lock(&dcache_lock);
+	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
+		if (!d_unhashed(dentry) || IS_ROOT(dentry)) {
+			spin_unlock(&dcache_lock);
+			return true;
+		}
+	}
+	spin_unlock(&dcache_lock);
+	return false;
+}
+
 /* Given fattrs, get a corresponding inode */
 struct inode *
 cifs_iget(struct super_block *sb, struct cifs_fattr *fattr)
@@ -769,12 +784,16 @@ retry_iget5_locked:
 
 	inode = iget5_locked(sb, hash, cifs_find_inode, cifs_init_inode, fattr);
 	if (inode) {
-		/* was there a problematic inode number collision? */
+		/* was there a potentially problematic inode collision? */
 		if (fattr->cf_flags & CIFS_FATTR_INO_COLLISION) {
-			iput(inode);
-			fattr->cf_uniqueid = iunique(sb, ROOT_I);
 			fattr->cf_flags &= ~CIFS_FATTR_INO_COLLISION;
-			goto retry_iget5_locked;
+
+			if (inode_has_hashed_dentries(inode)) {
+				cifs_autodisable_serverino(CIFS_SB(sb));
+				iput(inode);
+				fattr->cf_uniqueid = iunique(sb, ROOT_I);
+				goto retry_iget5_locked;
+			}
 		}
 
 		cifs_fattr_to_inode(inode, fattr);
diff --git a/fs/cifs/netmisc.c b/fs/cifs/netmisc.c
index c6721ee26db..f97851119e6 100644
--- a/fs/cifs/netmisc.c
+++ b/fs/cifs/netmisc.c
@@ -140,17 +140,18 @@ static const struct smb_to_posix_error mapping_table_ERRHRD[] = {
  * Returns 0 on failure.
  */
 static int
-cifs_inet_pton(const int address_family, const char *cp, void *dst)
+cifs_inet_pton(const int address_family, const char *cp, int len, void *dst)
 {
 	int ret = 0;
 
 	/* calculate length by finding first slash or NULL */
 	if (address_family == AF_INET)
-		ret = in4_pton(cp, -1 /* len */, dst, '\\', NULL);
+		ret = in4_pton(cp, len, dst, '\\', NULL);
 	else if (address_family == AF_INET6)
-		ret = in6_pton(cp, -1 /* len */, dst , '\\', NULL);
+		ret = in6_pton(cp, len, dst , '\\', NULL);
 
-	cFYI(DBG2, "address conversion returned %d for %s", ret, cp);
+	cFYI(DBG2, "address conversion returned %d for %*.*s",
+	     ret, len, len, cp);
 	if (ret > 0)
 		ret = 1;
 	return ret;
@@ -165,37 +166,39 @@ cifs_inet_pton(const int address_family, const char *cp, void *dst)
  * Returns 0 on failure.
  */
 int
-cifs_convert_address(struct sockaddr *dst, char *src)
+cifs_convert_address(struct sockaddr *dst, const char *src, int len)
 {
-	int rc;
-	char *pct, *endp;
+	int rc, alen, slen;
+	const char *pct;
+	char *endp, scope_id[13];
 	struct sockaddr_in *s4 = (struct sockaddr_in *) dst;
 	struct sockaddr_in6 *s6 = (struct sockaddr_in6 *) dst;
 
 	/* IPv4 address */
-	if (cifs_inet_pton(AF_INET, src, &s4->sin_addr.s_addr)) {
+	if (cifs_inet_pton(AF_INET, src, len, &s4->sin_addr.s_addr)) {
 		s4->sin_family = AF_INET;
 		return 1;
 	}
 
-	/* temporarily terminate string */
-	pct = strchr(src, '%');
-	if (pct)
-		*pct = '\0';
-
-	rc = cifs_inet_pton(AF_INET6, src, &s6->sin6_addr.s6_addr);
-
-	/* repair temp termination (if any) and make pct point to scopeid */
-	if (pct)
-		*pct++ = '%';
+	/* attempt to exclude the scope ID from the address part */
+	pct = memchr(src, '%', len);
+	alen = pct ? pct - src : len;
 
+	rc = cifs_inet_pton(AF_INET6, src, alen, &s6->sin6_addr.s6_addr);
 	if (!rc)
 		return rc;
 
 	s6->sin6_family = AF_INET6;
 	if (pct) {
+		/* grab the scope ID */
+		slen = len - (alen + 1);
+		if (slen <= 0 || slen > 12)
+			return 0;
+		memcpy(scope_id, pct + 1, slen);
+		scope_id[slen] = '\0';
+
 		s6->sin6_scope_id = (u32) simple_strtoul(pct, &endp, 0);
-		if (!*pct || *endp)
+		if (endp != scope_id + slen)
 			return 0;
 	}
 
@@ -203,10 +206,10 @@ cifs_convert_address(struct sockaddr *dst, char *src)
 }
 
 int
-cifs_fill_sockaddr(struct sockaddr *dst, char *src,
+cifs_fill_sockaddr(struct sockaddr *dst, const char *src, int len,
 		   const unsigned short int port)
 {
-	if (!cifs_convert_address(dst, src))
+	if (!cifs_convert_address(dst, src, len))
 		return 0;
 
 	switch (dst->sa_family) {
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..50d49f7e047
--- /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
+	  SMB2 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..400a04d5c9a
--- /dev/null
+++ b/net/dns_resolver/dns_key.c
@@ -0,0 +1,211 @@
+/* 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 <linux/err.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..03d5255f5cf
--- /dev/null
+++ b/net/dns_resolver/dns_query.c
@@ -0,0 +1,160 @@
+/* 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;
+
+	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__)