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Note that other outdated algorithms are left in place (some of which are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, 95 deletions

diff --git a/net/sunrpc/auth_gss/gss_krb5_mech.c b/net/sunrpc/auth_gss/gss_krb5_mech.c
index a84a5b28948442..ae9acf3a73898d 100644
--- a/net/sunrpc/auth_gss/gss_krb5_mech.c
+++ b/net/sunrpc/auth_gss/gss_krb5_mech.c
@@ -52,27 +52,6 @@ static const struct gss_krb5_enctype supported_gss_krb5_enctypes[] = {
 	},
 #endif	/* CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES */
 	/*
-	 * RC4-HMAC
-	 */
-	{
-	  .etype = ENCTYPE_ARCFOUR_HMAC,
-	  .ctype = CKSUMTYPE_HMAC_MD5_ARCFOUR,
-	  .name = "rc4-hmac",
-	  .encrypt_name = "ecb(arc4)",
-	  .cksum_name = "hmac(md5)",
-	  .encrypt = krb5_encrypt,
-	  .decrypt = krb5_decrypt,
-	  .mk_key = NULL,
-	  .signalg = SGN_ALG_HMAC_MD5,
-	  .sealalg = SEAL_ALG_MICROSOFT_RC4,
-	  .keybytes = 16,
-	  .keylength = 16,
-	  .blocksize = 1,
-	  .conflen = 8,
-	  .cksumlength = 8,
-	  .keyed_cksum = 1,
-	},
-	/*
 	 * 3DES
 	 */
 	{
@@ -401,78 +380,6 @@ out_err:
 	return -EINVAL;
 }
 
-/*
- * Note that RC4 depends on deriving keys using the sequence
- * number or the checksum of a token.  Therefore, the final keys
- * cannot be calculated until the token is being constructed!
- */
-static int
-context_derive_keys_rc4(struct krb5_ctx *ctx)
-{
-	struct crypto_shash *hmac;
-	char sigkeyconstant[] = "signaturekey";
-	int slen = strlen(sigkeyconstant) + 1;	/* include null terminator */
-	struct shash_desc *desc;
-	int err;
-
-	dprintk("RPC:       %s: entered\n", __func__);
-	/*
-	 * derive cksum (aka Ksign) key
-	 */
-	hmac = crypto_alloc_shash(ctx->gk5e->cksum_name, 0, 0);
-	if (IS_ERR(hmac)) {
-		dprintk("%s: error %ld allocating hash '%s'\n",
-			__func__, PTR_ERR(hmac), ctx->gk5e->cksum_name);
-		err = PTR_ERR(hmac);
-		goto out_err;
-	}
-
-	err = crypto_shash_setkey(hmac, ctx->Ksess, ctx->gk5e->keylength);
-	if (err)
-		goto out_err_free_hmac;
-
-
-	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac), GFP_NOFS);
-	if (!desc) {
-		dprintk("%s: failed to allocate hash descriptor for '%s'\n",
-			__func__, ctx->gk5e->cksum_name);
-		err = -ENOMEM;
-		goto out_err_free_hmac;
-	}
-
-	desc->tfm = hmac;
-
-	err = crypto_shash_digest(desc, sigkeyconstant, slen, ctx->cksum);
-	kfree_sensitive(desc);
-	if (err)
-		goto out_err_free_hmac;
-	/*
-	 * allocate hash, and skciphers for data and seqnum encryption
-	 */
-	ctx->enc = crypto_alloc_sync_skcipher(ctx->gk5e->encrypt_name, 0, 0);
-	if (IS_ERR(ctx->enc)) {
-		err = PTR_ERR(ctx->enc);
-		goto out_err_free_hmac;
-	}
-
-	ctx->seq = crypto_alloc_sync_skcipher(ctx->gk5e->encrypt_name, 0, 0);
-	if (IS_ERR(ctx->seq)) {
-		crypto_free_sync_skcipher(ctx->enc);
-		err = PTR_ERR(ctx->seq);
-		goto out_err_free_hmac;
-	}
-
-	dprintk("RPC:       %s: returning success\n", __func__);
-
-	err = 0;
-
-out_err_free_hmac:
-	crypto_free_shash(hmac);
-out_err:
-	dprintk("RPC:       %s: returning %d\n", __func__, err);
-	return err;
-}
-
 static int
 context_derive_keys_new(struct krb5_ctx *ctx, gfp_t gfp_mask)
 {
@@ -649,8 +556,6 @@ gss_import_v2_context(const void *p, const void *end, struct krb5_ctx *ctx,
 	switch (ctx->enctype) {
 	case ENCTYPE_DES3_CBC_RAW:
 		return context_derive_keys_des3(ctx, gfp_mask);
-	case ENCTYPE_ARCFOUR_HMAC:
-		return context_derive_keys_rc4(ctx);
 	case ENCTYPE_AES128_CTS_HMAC_SHA1_96:
 	case ENCTYPE_AES256_CTS_HMAC_SHA1_96:
 		return context_derive_keys_new(ctx, gfp_mask);