SUNRPC: remove RC4-HMAC-MD5 support from KerberosV

The RC4-HMAC-MD5 KerberosV algorithm is based on RFC 4757 [0], which
was specifically issued for interoperability with Windows 2000, but was
never intended to receive the same level of support. The RFC says

  The IETF Kerberos community supports publishing this specification as
  an informational document in order to describe this widely
  implemented technology.  However, while these encryption types
  provide the operations necessary to implement the base Kerberos
  specification [RFC4120], they do not provide all the required
  operations in the Kerberos cryptography framework [RFC3961].  As a
  result, it is not generally possible to implement potential
  extensions to Kerberos using these encryption types.  The Kerberos
  encryption type negotiation mechanism [RFC4537] provides one approach
  for using such extensions even when a Kerberos infrastructure uses
  long-term RC4 keys.  Because this specification does not implement
  operations required by RFC 3961 and because of security concerns with
  the use of RC4 and MD4 discussed in Section 8, this specification is
  not appropriate for publication on the standards track.

  The RC4-HMAC encryption types are used to ease upgrade of existing
  Windows NT environments, provide strong cryptography (128-bit key
  lengths), and provide exportable (meet United States government
  export restriction requirements) encryption.  This document describes
  the implementation of those encryption types.

Furthermore, this RFC was re-classified as 'historic' by RFC 8429 [1] in
2018, stating that 'none of the encryption types it specifies should be
used'

Note that other outdated algorithms are left in place (some of which are
guarded by CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES), so this should only
adversely affect interoperability with Windows NT/2000 systems that have
not received any updates since 2008 (but are connected to a network
nonetheless)

[0] https://tools.ietf.org/html/rfc4757
[1] https://tools.ietf.org/html/rfc8429

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 0 insertions, 87 deletions

diff --git a/net/sunrpc/auth_gss/gss_krb5_seqnum.c b/net/sunrpc/auth_gss/gss_krb5_seqnum.c
index 507105127095..fb117817ff5d 100644
--- a/net/sunrpc/auth_gss/gss_krb5_seqnum.c
+++ b/net/sunrpc/auth_gss/gss_krb5_seqnum.c
@@ -39,42 +39,6 @@
 # define RPCDBG_FACILITY        RPCDBG_AUTH
 #endif
 
-static s32
-krb5_make_rc4_seq_num(struct krb5_ctx *kctx, int direction, s32 seqnum,
-		      unsigned char *cksum, unsigned char *buf)
-{
-	struct crypto_sync_skcipher *cipher;
-	unsigned char *plain;
-	s32 code;
-
-	dprintk("RPC:       %s:\n", __func__);
-	cipher = crypto_alloc_sync_skcipher(kctx->gk5e->encrypt_name, 0, 0);
-	if (IS_ERR(cipher))
-		return PTR_ERR(cipher);
-
-	plain = kmalloc(8, GFP_NOFS);
-	if (!plain)
-		return -ENOMEM;
-
-	plain[0] = (unsigned char) ((seqnum >> 24) & 0xff);
-	plain[1] = (unsigned char) ((seqnum >> 16) & 0xff);
-	plain[2] = (unsigned char) ((seqnum >> 8) & 0xff);
-	plain[3] = (unsigned char) ((seqnum >> 0) & 0xff);
-	plain[4] = direction;
-	plain[5] = direction;
-	plain[6] = direction;
-	plain[7] = direction;
-
-	code = krb5_rc4_setup_seq_key(kctx, cipher, cksum);
-	if (code)
-		goto out;
-
-	code = krb5_encrypt(cipher, cksum, plain, buf, 8);
-out:
-	kfree(plain);
-	crypto_free_sync_skcipher(cipher);
-	return code;
-}
 s32
 krb5_make_seq_num(struct krb5_ctx *kctx,
 		struct crypto_sync_skcipher *key,
@@ -85,10 +49,6 @@ krb5_make_seq_num(struct krb5_ctx *kctx,
 	unsigned char *plain;
 	s32 code;
 
-	if (kctx->enctype == ENCTYPE_ARCFOUR_HMAC)
-		return krb5_make_rc4_seq_num(kctx, direction, seqnum,
-					     cksum, buf);
-
 	plain = kmalloc(8, GFP_NOFS);
 	if (!plain)
 		return -ENOMEM;
@@ -108,50 +68,6 @@ krb5_make_seq_num(struct krb5_ctx *kctx,
 	return code;
 }
 
-static s32
-krb5_get_rc4_seq_num(struct krb5_ctx *kctx, unsigned char *cksum,
-		     unsigned char *buf, int *direction, s32 *seqnum)
-{
-	struct crypto_sync_skcipher *cipher;
-	unsigned char *plain;
-	s32 code;
-
-	dprintk("RPC:       %s:\n", __func__);
-	cipher = crypto_alloc_sync_skcipher(kctx->gk5e->encrypt_name, 0, 0);
-	if (IS_ERR(cipher))
-		return PTR_ERR(cipher);
-
-	code = krb5_rc4_setup_seq_key(kctx, cipher, cksum);
-	if (code)
-		goto out;
-
-	plain = kmalloc(8, GFP_NOFS);
-	if (!plain) {
-		code = -ENOMEM;
-		goto out;
-	}
-
-	code = krb5_decrypt(cipher, cksum, buf, plain, 8);
-	if (code)
-		goto out_plain;
-
-	if ((plain[4] != plain[5]) || (plain[4] != plain[6])
-				   || (plain[4] != plain[7])) {
-		code = (s32)KG_BAD_SEQ;
-		goto out_plain;
-	}
-
-	*direction = plain[4];
-
-	*seqnum = ((plain[0] << 24) | (plain[1] << 16) |
-					(plain[2] << 8) | (plain[3]));
-out_plain:
-	kfree(plain);
-out:
-	crypto_free_sync_skcipher(cipher);
-	return code;
-}
-
 s32
 krb5_get_seq_num(struct krb5_ctx *kctx,
 	       unsigned char *cksum,
@@ -164,9 +80,6 @@ krb5_get_seq_num(struct krb5_ctx *kctx,
 
 	dprintk("RPC:       krb5_get_seq_num:\n");
 
-	if (kctx->enctype == ENCTYPE_ARCFOUR_HMAC)
-		return krb5_get_rc4_seq_num(kctx, cksum, buf,
-					    direction, seqnum);
 	plain = kmalloc(8, GFP_NOFS);
 	if (!plain)
 		return -ENOMEM;