signing.c

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/* 
   Unix SMB/CIFS implementation.

   SMB2 Signing Code

   Copyright (C) Andrew Tridgell <[e-mail]> 2008

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "libcli/raw/libcliraw.h"
#include "libcli/smb2/smb2.h"
#include "libcli/smb2/smb2_calls.h"
#include "heimdal/lib/hcrypto/sha.h"

/*
  NOTE: this code does not yet interoperate with the windows SMB2
  implementation. We are waiting on feedback on the docs to find out
  why
 */


/*
  setup signing on a transport
 */
NTSTATUS smb2_start_signing(struct smb2_transport *transport)
{
	if (transport->signing.session_key.length != 16) {
		DEBUG(2,("Wrong session key length %u for SMB2 signing\n",
			 (unsigned)transport->signing.session_key.length));
		return NT_STATUS_ACCESS_DENIED;
	}

	transport->signing.signing_started = true;
	return NT_STATUS_OK;
}

/*
  sign an outgoing message
 */
NTSTATUS smb2_sign_message(struct smb2_request *req)
{
	struct smb2_request_buffer *buf = &req->out;
	uint64_t session_id;
	SHA256_CTX m;
	uint8_t res[32];

	if (!req->transport->signing.doing_signing ||
	    !req->transport->signing.signing_started) {
		return NT_STATUS_OK;
	}

	if (buf->size < NBT_HDR_SIZE + SMB2_HDR_SIGNATURE + 16) {
		/* can't sign non-SMB2 messages */
		return NT_STATUS_OK;
	}

	session_id = BVAL(buf->hdr, SMB2_HDR_SESSION_ID);
	if (session_id == 0) {
		/* we don't sign messages with a zero session_id. See
		   MS-SMB2 3.2.4.1.1 */
		return NT_STATUS_OK;		
	}

	if (req->transport->signing.session_key.length != 16) {
		DEBUG(2,("Wrong session key length %u for SMB2 signing\n",
			 (unsigned)req->transport->signing.session_key.length));
		return NT_STATUS_ACCESS_DENIED;
	}

	memset(buf->hdr + SMB2_HDR_SIGNATURE, 0, 16);

	SIVAL(buf->hdr, SMB2_HDR_FLAGS, IVAL(buf->hdr, SMB2_HDR_FLAGS) | SMB2_HDR_FLAG_SIGNED);

	ZERO_STRUCT(m);
	SHA256_Init(&m);
	SHA256_Update(&m, req->transport->signing.session_key.data, 
		      req->transport->signing.session_key.length);
	SHA256_Update(&m, buf->buffer+NBT_HDR_SIZE, buf->size-NBT_HDR_SIZE);
	SHA256_Final(res, &m);

	DEBUG(5,("signed SMB2 message of size %u\n", (unsigned)buf->size - NBT_HDR_SIZE));

	memcpy(buf->hdr + SMB2_HDR_SIGNATURE, res, 16);

	if (DEBUGLVL(5)) {
		/* check our own signature */
		smb2_check_signature(req->transport, buf->buffer, buf->size);
	}

	return NT_STATUS_OK;	
}

/*
  check an incoming signature
 */
NTSTATUS smb2_check_signature(struct smb2_transport *transport,
			      uint8_t *buffer, uint_t length)
{
	uint64_t session_id;
	SHA256_CTX m;
	uint8_t res[SHA256_DIGEST_LENGTH];
	uint8_t sig[16];

	if (!transport->signing.signing_started ||
	    !transport->signing.doing_signing) {
		return NT_STATUS_OK;
	}

	if (length < NBT_HDR_SIZE + SMB2_HDR_SIGNATURE + 16) {
		/* can't check non-SMB2 messages */
		return NT_STATUS_OK;
	}

	session_id = BVAL(buffer+NBT_HDR_SIZE, SMB2_HDR_SESSION_ID);
	if (session_id == 0) {
		/* don't sign messages with a zero session_id. See
		   MS-SMB2 3.2.4.1.1 */
		return NT_STATUS_OK;		
	}

	if (transport->signing.session_key.length == 0) {
		/* we don't have the session key yet */
		return NT_STATUS_OK;
	}

	if (transport->signing.session_key.length != 16) {
		DEBUG(2,("Wrong session key length %u for SMB2 signing\n",
			 (unsigned)transport->signing.session_key.length));
		return NT_STATUS_ACCESS_DENIED;
	}

	memcpy(sig, buffer+NBT_HDR_SIZE+SMB2_HDR_SIGNATURE, 16);

	memset(buffer + NBT_HDR_SIZE + SMB2_HDR_SIGNATURE, 0, 16);

	ZERO_STRUCT(m);
	SHA256_Init(&m);
	SHA256_Update(&m, transport->signing.session_key.data,    16);
	SHA256_Update(&m, buffer+NBT_HDR_SIZE, length-NBT_HDR_SIZE);
	SHA256_Final(res, &m);

	memcpy(buffer+NBT_HDR_SIZE+SMB2_HDR_SIGNATURE, sig, 16);

	if (memcmp(res, sig, 16) != 0) {
		DEBUG(0,("Bad SMB2 signature for message of size %u\n", length));
		dump_data(0, sig, 16);
		dump_data(0, res, 16);
		return NT_STATUS_ACCESS_DENIED;
	}

	return NT_STATUS_OK;	
}