[CIFS] DNS name resolution helper upcall for cifs

	Adds additional option CIFS_DFS_UPCALL to fs/Kconfig for enabling
        DFS support.  Resolved IP address is saved as a string in the
	key payload.

	Igor has a series of related patches that will follow which finish up
	CIFS DFS support

Acked-by: Igor Mammedov <niallain@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

3 files changed, 42 insertions, 14 deletions

diff --git a/fs/Kconfig b/fs/Kconfig
index 487236c65837..18cd22149466 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -1905,13 +1905,15 @@ config CIFS
           file servers such as Windows 2000 (including Windows 2003, NT 4  
           and Windows XP) as well by Samba (which provides excellent CIFS
           server support for Linux and many other operating systems). Limited
-          support for OS/2 and Windows ME and similar servers is provided as well.
-
-          The intent of the cifs module is to provide an advanced
-          network file system client for mounting to CIFS compliant servers,
-          including support for dfs (hierarchical name space), secure per-user
-          session establishment, safe distributed caching (oplock), optional
-          packet signing, Unicode and other internationalization improvements. 
+          support for OS/2 and Windows ME and similar servers is provided as
+          well.
+
+          The cifs module provides an advanced network file system
+          client for mounting to CIFS compliant servers.  It includes
+          support for DFS (hierarchical name space), secure per-user
+          session establishment via Kerberos or NTLM or NTLMv2,
+          safe distributed caching (oplock), optional packet
+          signing, Unicode and other internationalization improvements.
           If you need to mount to Samba or Windows from this machine, say Y.
 
 config CIFS_STATS
@@ -1943,7 +1945,8 @@ config CIFS_WEAK_PW_HASH
           (since 1997) support stronger NTLM (and even NTLMv2 and Kerberos)
           security mechanisms. These hash the password more securely
           than the mechanisms used in the older LANMAN version of the
-          SMB protocol needed to establish sessions with old SMB servers.
+          SMB protocol but LANMAN based authentication is needed to
+          establish sessions with some old SMB servers.
 
           Enabling this option allows the cifs module to mount to older
           LANMAN based servers such as OS/2 and Windows 95, but such
@@ -1951,8 +1954,8 @@ config CIFS_WEAK_PW_HASH
           security mechanisms if you are on a public network.  Unless you
           have a need to access old SMB servers (and are on a private 
           network) you probably want to say N.  Even if this support
-          is enabled in the kernel build, they will not be used
-          automatically. At runtime LANMAN mounts are disabled but
+          is enabled in the kernel build, LANMAN authentication will not be
+          used automatically. At runtime LANMAN mounts are disabled but
           can be set to required (or optional) either in
           /proc/fs/cifs (see fs/cifs/README for more detail) or via an
           option on the mount command. This support is disabled by 
@@ -2018,12 +2021,22 @@ config CIFS_UPCALL
           depends on CIFS_EXPERIMENTAL
           depends on KEYS
           help
-            Enables an upcall mechanism for CIFS which will be used to contact
-            userspace helper utilities to provide SPNEGO packaged Kerberos
-            tickets which are needed to mount to certain secure servers
+            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_DFS_UPCALL
+          bool "DFS feature support (EXPERIMENTAL)"
+          depends on CIFS_EXPERIMENTAL
+          depends on KEYS
+          help
+            Enables an upcall mechanism for CIFS which contacts userspace
+            helper utilities to provide server name resolution (host names to
+            IP addresses) which is needed for implicit mounts of DFS junction
+            points. If unsure, say N.
+
 config NCP_FS
         tristate "NCP file system support (to mount NetWare volumes)"
         depends on IPX!=n || INET
diff --git a/fs/cifs/Makefile b/fs/cifs/Makefile
index 45e42fb97c19..09898b8dc69b 100644
--- a/fs/cifs/Makefile
+++ b/fs/cifs/Makefile
@@ -9,3 +9,5 @@ cifs-y := cifsfs.o cifssmb.o cifs_debug.o connect.o dir.o file.o inode.o \
           readdir.o ioctl.o sess.o export.o cifsacl.o
 
 cifs-$(CONFIG_CIFS_UPCALL) += cifs_spnego.o
+
+cifs-$(CONFIG_CIFS_DFS_UPCALL) += dns_resolve.o
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 093beaa3900d..000b4a5d3219 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -44,6 +44,7 @@
 #include "cifs_fs_sb.h"
 #include <linux/mm.h>
 #include <linux/key-type.h>
+#include "dns_resolve.h"
 #include "cifs_spnego.h"
 #define CIFS_MAGIC_NUMBER 0xFF534D42    /* the first four bytes of SMB PDUs */
 
@@ -1015,11 +1016,16 @@ init_cifs(void)
         if (rc)
                 goto out_unregister_filesystem;
 #endif
+#ifdef CONFIG_CIFS_DFS_UPCALL
+        rc = register_key_type(&key_type_dns_resolver);
+        if (rc)
+                goto out_unregister_key_type;
+#endif
         oplockThread = kthread_run(cifs_oplock_thread, NULL, "cifsoplockd");
         if (IS_ERR(oplockThread)) {
                 rc = PTR_ERR(oplockThread);
                 cERROR(1, ("error %d create oplock thread", rc));
-                goto out_unregister_key_type;
+                goto out_unregister_dfs_key_type;
         }
 
         dnotifyThread = kthread_run(cifs_dnotify_thread, NULL, "cifsdnotifyd");
@@ -1033,7 +1039,11 @@ init_cifs(void)
 
  out_stop_oplock_thread:
         kthread_stop(oplockThread);
+ out_unregister_dfs_key_type:
+#ifdef CONFIG_CIFS_DFS_UPCALL
+        unregister_key_type(&key_type_dns_resolver);
  out_unregister_key_type:
+#endif
 #ifdef CONFIG_CIFS_UPCALL
         unregister_key_type(&cifs_spnego_key_type);
  out_unregister_filesystem:
@@ -1059,6 +1069,9 @@ exit_cifs(void)
 #ifdef CONFIG_PROC_FS
         cifs_proc_clean();
 #endif
+#ifdef CONFIG_CIFS_DFS_UPCALL
+        unregister_key_type(&key_type_dns_resolver);
+#endif
 #ifdef CONFIG_CIFS_UPCALL
         unregister_key_type(&cifs_spnego_key_type);
 #endif