SUNRPC: Enable rpcsec_gss_krb5.ko to be built without CRYPTO_DES

Because the DES block cipher has been deprecated by Internet
standard, highly secure configurations might require that DES
support be blacklisted or not installed. NFS Kerberos should still
be able to work correctly with only the AES-based enctypes in that
situation.

Also note that MIT Kerberos has begun a deprecation process for DES
encryption types. Their README for 1.19.3 states:

> Beginning with the krb5-1.19 release, a warning will be issued
> if initial credentials are acquired using the des3-cbc-sha1
> encryption type.  In future releases, this encryption type will
> be disabled by default and eventually removed.
>
> Beginning with the krb5-1.18 release, single-DES encryption
> types have been removed.

Aside from the CONFIG option name change, there are two important
policy changes:

1. The 'insecure enctype' group is now disabled by default.
   Distributors have to take action to enable support for deprecated
   enctypes. Implementation of these enctypes will be removed in a
   future kernel release.

2. des3-cbc-sha1 is now considered part of the 'insecure enctype'
   group, having been deprecated by RFC 8429, and is thus disabled
   by default

After this patch is applied, SunRPC support can be built with
Kerberos 5 support but without CRYPTO_DES enabled in the kernel.
And, when these enctypes are disabled, the Linux kernel's SunRPC
RPCSEC GSS implementation fully complies with BCP 179 / RFC 6649
and BCP 218 / RFC 8429.

Tested-by: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 44 insertions, 14 deletions

diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig
index bbbb5af0af13..82ecb534795a 100644
--- a/net/sunrpc/Kconfig
+++ b/net/sunrpc/Kconfig
@@ -19,10 +19,10 @@ config SUNRPC_SWAP
 config RPCSEC_GSS_KRB5
 	tristate "Secure RPC: Kerberos V mechanism"
 	depends on SUNRPC && CRYPTO
-	depends on CRYPTO_MD5 && CRYPTO_DES && CRYPTO_CBC && CRYPTO_CTS
-	depends on CRYPTO_ECB && CRYPTO_HMAC && CRYPTO_SHA1 && CRYPTO_AES
 	default y
 	select SUNRPC_GSS
+	select CRYPTO_SKCIPHER
+	select CRYPTO_HASH
 	help
 	  Choose Y here to enable Secure RPC using the Kerberos version 5
 	  GSS-API mechanism (RFC 1964).
@@ -34,21 +34,51 @@ config RPCSEC_GSS_KRB5
 
 	  If unsure, say Y.
 
-config SUNRPC_DISABLE_INSECURE_ENCTYPES
-	bool "Secure RPC: Disable insecure Kerberos encryption types"
+config RPCSEC_GSS_KRB5_SIMPLIFIED
+	bool
+	depends on RPCSEC_GSS_KRB5
+
+config RPCSEC_GSS_KRB5_CRYPTOSYSTEM
+	bool
+	depends on RPCSEC_GSS_KRB5
+
+config RPCSEC_GSS_KRB5_ENCTYPES_DES
+	bool "Enable Kerberos enctypes based on DES (deprecated)"
 	depends on RPCSEC_GSS_KRB5
+	depends on CRYPTO_CBC && CRYPTO_CTS && CRYPTO_ECB
+	depends on CRYPTO_HMAC && CRYPTO_MD5 && CRYPTO_SHA1
+	depends on CRYPTO_DES
 	default n
+	select RPCSEC_GSS_KRB5_SIMPLIFIED
+	help
+	  Choose Y to enable the use of deprecated Kerberos 5
+	  encryption types that utilize Data Encryption Standard
+	  (DES) based ciphers. These include des-cbc-md5,
+	  des-cbc-crc, and des-cbc-md4, which were deprecated by
+	  RFC 6649, and des3-cbc-sha1, which was deprecated by RFC
+	  8429.
+
+	  These encryption types are known to be insecure, therefore
+	  the default setting of this option is N. Support for these
+	  encryption types is available only for compatibility with
+	  legacy NFS client and server implementations.
+
+	  Removal of support is planned for a subsequent kernel
+	  release.
+
+config RPCSEC_GSS_KRB5_ENCTYPES_AES_SHA1
+	bool "Enable Kerberos enctypes based on AES and SHA-1"
+	depends on RPCSEC_GSS_KRB5
+	depends on CRYPTO_CBC && CRYPTO_CTS
+	depends on CRYPTO_HMAC && CRYPTO_SHA1
+	depends on CRYPTO_AES
+	default y
+	select RPCSEC_GSS_KRB5_CRYPTOSYSTEM
 	help
-	  Choose Y here to disable the use of deprecated encryption types
-	  with the Kerberos version 5 GSS-API mechanism (RFC 1964). The
-	  deprecated encryption types include DES-CBC-MD5, DES-CBC-CRC,
-	  and DES-CBC-MD4. These types were deprecated by RFC 6649 because
-	  they were found to be insecure.
-
-	  N is the default because many sites have deployed KDCs and
-	  keytabs that contain only these deprecated encryption types.
-	  Choosing Y prevents the use of known-insecure encryption types
-	  but might result in compatibility problems.
+	  Choose Y to enable the use of Kerberos 5 encryption types
+	  that utilize Advanced Encryption Standard (AES) ciphers and
+	  SHA-1 digests. These include aes128-cts-hmac-sha1-96 and
+	  aes256-cts-hmac-sha1-96.
 
 config SUNRPC_DEBUG
 	bool "RPC: Enable dprintk debugging"