4 files changed, 56 insertions, 205 deletions

diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
index 5739fd7f88b4..57f0aa9f141f 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 8a2cf129e535..2a0c892959f4 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 aa967e7917f8..0eb87026cad3 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 5d7f291df162..d3f5d27f4d06 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 */