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![Ard Biesheuvel](/assets/img/avatar_default.png)
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by RFC 8429 [1] in 2018, stating that 'none of the encryption types it specifies should be used' Note that other outdated algorithms are left in place (some of which are guarded by CONFIG_SUNRPC_DISABLE_INSECURE_ENCTYPES), so this should only adversely affect interoperability with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>
226 lines
6.7 KiB
C
226 lines
6.7 KiB
C
/*
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* linux/net/sunrpc/gss_krb5_unseal.c
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*
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* Adapted from MIT Kerberos 5-1.2.1 lib/gssapi/krb5/k5unseal.c
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*
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* Copyright (c) 2000-2008 The Regents of the University of Michigan.
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* All rights reserved.
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*
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* Andy Adamson <andros@umich.edu>
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*/
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/*
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* Copyright 1993 by OpenVision Technologies, Inc.
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*
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* Permission to use, copy, modify, distribute, and sell this software
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* and its documentation for any purpose is hereby granted without fee,
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* provided that the above copyright notice appears in all copies and
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* that both that copyright notice and this permission notice appear in
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* supporting documentation, and that the name of OpenVision not be used
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* in advertising or publicity pertaining to distribution of the software
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* without specific, written prior permission. OpenVision makes no
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* representations about the suitability of this software for any
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* purpose. It is provided "as is" without express or implied warranty.
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*
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* OPENVISION DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
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* EVENT SHALL OPENVISION BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
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* USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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* OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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* PERFORMANCE OF THIS SOFTWARE.
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*/
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/*
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* Copyright (C) 1998 by the FundsXpress, INC.
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*
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* All rights reserved.
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*
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* Export of this software from the United States of America may require
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* a specific license from the United States Government. It is the
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* responsibility of any person or organization contemplating export to
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* obtain such a license before exporting.
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*
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* WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
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* distribute this software and its documentation for any purpose and
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* without fee is hereby granted, provided that the above copyright
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* notice appear in all copies and that both that copyright notice and
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* this permission notice appear in supporting documentation, and that
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* the name of FundsXpress. not be used in advertising or publicity pertaining
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* to distribution of the software without specific, written prior
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* permission. FundsXpress makes no representations about the suitability of
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* this software for any purpose. It is provided "as is" without express
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* or implied warranty.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*/
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#include <linux/types.h>
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#include <linux/jiffies.h>
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#include <linux/sunrpc/gss_krb5.h>
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#include <linux/crypto.h>
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#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
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# define RPCDBG_FACILITY RPCDBG_AUTH
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#endif
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/* read_token is a mic token, and message_buffer is the data that the mic was
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* supposedly taken over. */
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static u32
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gss_verify_mic_v1(struct krb5_ctx *ctx,
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struct xdr_buf *message_buffer, struct xdr_netobj *read_token)
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{
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int signalg;
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int sealalg;
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char cksumdata[GSS_KRB5_MAX_CKSUM_LEN];
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struct xdr_netobj md5cksum = {.len = sizeof(cksumdata),
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.data = cksumdata};
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s32 now;
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int direction;
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u32 seqnum;
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unsigned char *ptr = (unsigned char *)read_token->data;
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int bodysize;
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u8 *cksumkey;
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dprintk("RPC: krb5_read_token\n");
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if (g_verify_token_header(&ctx->mech_used, &bodysize, &ptr,
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read_token->len))
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return GSS_S_DEFECTIVE_TOKEN;
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if ((ptr[0] != ((KG_TOK_MIC_MSG >> 8) & 0xff)) ||
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(ptr[1] != (KG_TOK_MIC_MSG & 0xff)))
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return GSS_S_DEFECTIVE_TOKEN;
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/* XXX sanity-check bodysize?? */
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signalg = ptr[2] + (ptr[3] << 8);
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if (signalg != ctx->gk5e->signalg)
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return GSS_S_DEFECTIVE_TOKEN;
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sealalg = ptr[4] + (ptr[5] << 8);
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if (sealalg != SEAL_ALG_NONE)
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return GSS_S_DEFECTIVE_TOKEN;
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if ((ptr[6] != 0xff) || (ptr[7] != 0xff))
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return GSS_S_DEFECTIVE_TOKEN;
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if (ctx->gk5e->keyed_cksum)
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cksumkey = ctx->cksum;
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else
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cksumkey = NULL;
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if (make_checksum(ctx, ptr, 8, message_buffer, 0,
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cksumkey, KG_USAGE_SIGN, &md5cksum))
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return GSS_S_FAILURE;
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if (memcmp(md5cksum.data, ptr + GSS_KRB5_TOK_HDR_LEN,
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ctx->gk5e->cksumlength))
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return GSS_S_BAD_SIG;
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/* it got through unscathed. Make sure the context is unexpired */
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now = ktime_get_real_seconds();
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if (now > ctx->endtime)
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return GSS_S_CONTEXT_EXPIRED;
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/* do sequencing checks */
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if (krb5_get_seq_num(ctx, ptr + GSS_KRB5_TOK_HDR_LEN, ptr + 8,
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&direction, &seqnum))
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return GSS_S_FAILURE;
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if ((ctx->initiate && direction != 0xff) ||
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(!ctx->initiate && direction != 0))
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return GSS_S_BAD_SIG;
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return GSS_S_COMPLETE;
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}
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static u32
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gss_verify_mic_v2(struct krb5_ctx *ctx,
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struct xdr_buf *message_buffer, struct xdr_netobj *read_token)
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{
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char cksumdata[GSS_KRB5_MAX_CKSUM_LEN];
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struct xdr_netobj cksumobj = {.len = sizeof(cksumdata),
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.data = cksumdata};
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time64_t now;
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u8 *ptr = read_token->data;
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u8 *cksumkey;
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u8 flags;
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int i;
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unsigned int cksum_usage;
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__be16 be16_ptr;
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dprintk("RPC: %s\n", __func__);
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memcpy(&be16_ptr, (char *) ptr, 2);
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if (be16_to_cpu(be16_ptr) != KG2_TOK_MIC)
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return GSS_S_DEFECTIVE_TOKEN;
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flags = ptr[2];
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if ((!ctx->initiate && (flags & KG2_TOKEN_FLAG_SENTBYACCEPTOR)) ||
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(ctx->initiate && !(flags & KG2_TOKEN_FLAG_SENTBYACCEPTOR)))
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return GSS_S_BAD_SIG;
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if (flags & KG2_TOKEN_FLAG_SEALED) {
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dprintk("%s: token has unexpected sealed flag\n", __func__);
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return GSS_S_FAILURE;
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}
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for (i = 3; i < 8; i++)
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if (ptr[i] != 0xff)
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return GSS_S_DEFECTIVE_TOKEN;
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if (ctx->initiate) {
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cksumkey = ctx->acceptor_sign;
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cksum_usage = KG_USAGE_ACCEPTOR_SIGN;
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} else {
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cksumkey = ctx->initiator_sign;
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cksum_usage = KG_USAGE_INITIATOR_SIGN;
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}
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if (make_checksum_v2(ctx, ptr, GSS_KRB5_TOK_HDR_LEN, message_buffer, 0,
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cksumkey, cksum_usage, &cksumobj))
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return GSS_S_FAILURE;
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if (memcmp(cksumobj.data, ptr + GSS_KRB5_TOK_HDR_LEN,
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ctx->gk5e->cksumlength))
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return GSS_S_BAD_SIG;
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/* it got through unscathed. Make sure the context is unexpired */
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now = ktime_get_real_seconds();
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if (now > ctx->endtime)
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return GSS_S_CONTEXT_EXPIRED;
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/*
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* NOTE: the sequence number at ptr + 8 is skipped, rpcsec_gss
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* doesn't want it checked; see page 6 of rfc 2203.
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*/
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return GSS_S_COMPLETE;
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}
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u32
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gss_verify_mic_kerberos(struct gss_ctx *gss_ctx,
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struct xdr_buf *message_buffer,
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struct xdr_netobj *read_token)
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{
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struct krb5_ctx *ctx = gss_ctx->internal_ctx_id;
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switch (ctx->enctype) {
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default:
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BUG();
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case ENCTYPE_DES_CBC_RAW:
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case ENCTYPE_DES3_CBC_RAW:
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return gss_verify_mic_v1(ctx, message_buffer, read_token);
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case ENCTYPE_AES128_CTS_HMAC_SHA1_96:
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case ENCTYPE_AES256_CTS_HMAC_SHA1_96:
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return gss_verify_mic_v2(ctx, message_buffer, read_token);
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}
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}
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