linux/net/rxrpc/rxkad.c

/* Kerberos-based RxRPC security
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/udp.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <linux/ctype.h>
#include <net/sock.h>
#include <net/af_rxrpc.h>
#define rxrpc_debug rxkad_debug
#include "ar-internal.h"

#define RXKAD_VERSION			2
#define MAXKRB5TICKETLEN		1024
#define RXKAD_TKT_TYPE_KERBEROS_V5	256
#define ANAME_SZ			40	/* size of authentication name */
#define INST_SZ				40	/* size of principal's instance */
#define REALM_SZ			40	/* size of principal's auth domain */
#define SNAME_SZ			40	/* size of service name */

unsigned rxrpc_debug;
module_param_named(debug, rxrpc_debug, uint, S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(rxrpc_debug, "rxkad debugging mask");

struct rxkad_level1_hdr {
	__be32	data_size;	/* true data size (excluding padding) */
};

struct rxkad_level2_hdr {
	__be32	data_size;	/* true data size (excluding padding) */
	__be32	checksum;	/* decrypted data checksum */
};

MODULE_DESCRIPTION("RxRPC network protocol type-2 security (Kerberos)");
MODULE_AUTHOR("Red Hat, Inc.");
MODULE_LICENSE("GPL");

/*
 * this holds a pinned cipher so that keventd doesn't get called by the cipher
 * alloc routine, but since we have it to hand, we use it to decrypt RESPONSE
 * packets
 */
static struct crypto_blkcipher *rxkad_ci;
static DEFINE_MUTEX(rxkad_ci_mutex);

/*
 * initialise connection security
 */
static int rxkad_init_connection_security(struct rxrpc_connection *conn)
{
	struct rxrpc_key_payload *payload;
	struct crypto_blkcipher *ci;
	int ret;

	_enter("{%d},{%x}", conn->debug_id, key_serial(conn->key));

	payload = conn->key->payload.data;
	conn->security_ix = payload->k.security_index;

	ci = crypto_alloc_blkcipher("pcbc(fcrypt)", 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(ci)) {
		_debug("no cipher");
		ret = PTR_ERR(ci);
		goto error;
	}

	if (crypto_blkcipher_setkey(ci, payload->k.session_key,
				    sizeof(payload->k.session_key)) < 0)
		BUG();

	switch (conn->security_level) {
	case RXRPC_SECURITY_PLAIN:
		break;
	case RXRPC_SECURITY_AUTH:
		conn->size_align = 8;
		conn->security_size = sizeof(struct rxkad_level1_hdr);
		conn->header_size += sizeof(struct rxkad_level1_hdr);
		break;
	case RXRPC_SECURITY_ENCRYPT:
		conn->size_align = 8;
		conn->security_size = sizeof(struct rxkad_level2_hdr);
		conn->header_size += sizeof(struct rxkad_level2_hdr);
		break;
	default:
		ret = -EKEYREJECTED;
		goto error;
	}

	conn->cipher = ci;
	ret = 0;
error:
	_leave(" = %d", ret);
	return ret;
}

/*
 * prime the encryption state with the invariant parts of a connection's
 * description
 */
static void rxkad_prime_packet_security(struct rxrpc_connection *conn)
{
	struct rxrpc_key_payload *payload;
	struct blkcipher_desc desc;
	struct scatterlist sg[2];
	struct rxrpc_crypt iv;
	struct {
		__be32 x[4];
	} tmpbuf __attribute__((aligned(16))); /* must all be in same page */

	_enter("");

	if (!conn->key)
		return;

	payload = conn->key->payload.data;
	memcpy(&iv, payload->k.session_key, sizeof(iv));

	desc.tfm = conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	tmpbuf.x[0] = conn->epoch;
	tmpbuf.x[1] = conn->cid;
	tmpbuf.x[2] = 0;
	tmpbuf.x[3] = htonl(conn->security_ix);

	sg_init_one(&sg[0], &tmpbuf, sizeof(tmpbuf));
	sg_init_one(&sg[1], &tmpbuf, sizeof(tmpbuf));
	crypto_blkcipher_encrypt_iv(&desc, &sg[0], &sg[1], sizeof(tmpbuf));

	memcpy(&conn->csum_iv, &tmpbuf.x[2], sizeof(conn->csum_iv));
	ASSERTCMP(conn->csum_iv.n[0], ==, tmpbuf.x[2]);

	_leave("");
}

/*
 * partially encrypt a packet (level 1 security)
 */
static int rxkad_secure_packet_auth(const struct rxrpc_call *call,
				    struct sk_buff *skb,
				    u32 data_size,
				    void *sechdr)
{
	struct rxrpc_skb_priv *sp;
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv;
	struct scatterlist sg[2];
	struct {
		struct rxkad_level1_hdr hdr;
		__be32	first;	/* first four bytes of data and padding */
	} tmpbuf __attribute__((aligned(8))); /* must all be in same page */
	u16 check;

	sp = rxrpc_skb(skb);

	_enter("");

	check = ntohl(sp->hdr.seq ^ sp->hdr.callNumber);
	data_size |= (u32) check << 16;

	tmpbuf.hdr.data_size = htonl(data_size);
	memcpy(&tmpbuf.first, sechdr + 4, sizeof(tmpbuf.first));

	/* start the encryption afresh */
	memset(&iv, 0, sizeof(iv));
	desc.tfm = call->conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	sg_init_one(&sg[0], &tmpbuf, sizeof(tmpbuf));
	sg_init_one(&sg[1], &tmpbuf, sizeof(tmpbuf));
	crypto_blkcipher_encrypt_iv(&desc, &sg[0], &sg[1], sizeof(tmpbuf));

	memcpy(sechdr, &tmpbuf, sizeof(tmpbuf));

	_leave(" = 0");
	return 0;
}

/*
 * wholly encrypt a packet (level 2 security)
 */
static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call,
					struct sk_buff *skb,
					u32 data_size,
					void *sechdr)
{
	const struct rxrpc_key_payload *payload;
	struct rxkad_level2_hdr rxkhdr
		__attribute__((aligned(8))); /* must be all on one page */
	struct rxrpc_skb_priv *sp;
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv;
	struct scatterlist sg[16];
	struct sk_buff *trailer;
	unsigned len;
	u16 check;
	int nsg;

	sp = rxrpc_skb(skb);

	_enter("");

	check = ntohl(sp->hdr.seq ^ sp->hdr.callNumber);

	rxkhdr.data_size = htonl(data_size | (u32) check << 16);
	rxkhdr.checksum = 0;

	/* encrypt from the session key */
	payload = call->conn->key->payload.data;
	memcpy(&iv, payload->k.session_key, sizeof(iv));
	desc.tfm = call->conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	sg_init_one(&sg[0], sechdr, sizeof(rxkhdr));
	sg_init_one(&sg[1], &rxkhdr, sizeof(rxkhdr));
	crypto_blkcipher_encrypt_iv(&desc, &sg[0], &sg[1], sizeof(rxkhdr));

	/* we want to encrypt the skbuff in-place */
	nsg = skb_cow_data(skb, 0, &trailer);
	if (nsg < 0 || nsg > 16)
		return -ENOMEM;

	len = data_size + call->conn->size_align - 1;
	len &= ~(call->conn->size_align - 1);

	sg_init_table(sg, nsg);
	skb_to_sgvec(skb, sg, 0, len);
	crypto_blkcipher_encrypt_iv(&desc, sg, sg, len);

	_leave(" = 0");
	return 0;
}

/*
 * checksum an RxRPC packet header
 */
static int rxkad_secure_packet(const struct rxrpc_call *call,
				struct sk_buff *skb,
				size_t data_size,
				void *sechdr)
{
	struct rxrpc_skb_priv *sp;
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv;
	struct scatterlist sg[2];
	struct {
		__be32 x[2];
	} tmpbuf __attribute__((aligned(8))); /* must all be in same page */
	__be32 x;
	int ret;

	sp = rxrpc_skb(skb);

	_enter("{%d{%x}},{#%u},%zu,",
	       call->debug_id, key_serial(call->conn->key), ntohl(sp->hdr.seq),
	       data_size);

	if (!call->conn->cipher)
		return 0;

	ret = key_validate(call->conn->key);
	if (ret < 0)
		return ret;

	/* continue encrypting from where we left off */
	memcpy(&iv, call->conn->csum_iv.x, sizeof(iv));
	desc.tfm = call->conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	/* calculate the security checksum */
	x = htonl(call->channel << (32 - RXRPC_CIDSHIFT));
	x |= sp->hdr.seq & cpu_to_be32(0x3fffffff);
	tmpbuf.x[0] = sp->hdr.callNumber;
	tmpbuf.x[1] = x;

	sg_init_one(&sg[0], &tmpbuf, sizeof(tmpbuf));
	sg_init_one(&sg[1], &tmpbuf, sizeof(tmpbuf));
	crypto_blkcipher_encrypt_iv(&desc, &sg[0], &sg[1], sizeof(tmpbuf));

	x = ntohl(tmpbuf.x[1]);
	x = (x >> 16) & 0xffff;
	if (x == 0)
		x = 1; /* zero checksums are not permitted */
	sp->hdr.cksum = htons(x);

	switch (call->conn->security_level) {
	case RXRPC_SECURITY_PLAIN:
		ret = 0;
		break;
	case RXRPC_SECURITY_AUTH:
		ret = rxkad_secure_packet_auth(call, skb, data_size, sechdr);
		break;
	case RXRPC_SECURITY_ENCRYPT:
		ret = rxkad_secure_packet_encrypt(call, skb, data_size,
						  sechdr);
		break;
	default:
		ret = -EPERM;
		break;
	}

	_leave(" = %d [set %hx]", ret, x);
	return ret;
}

/*
 * decrypt partial encryption on a packet (level 1 security)
 */
static int rxkad_verify_packet_auth(const struct rxrpc_call *call,
				    struct sk_buff *skb,
				    u32 *_abort_code)
{
	struct rxkad_level1_hdr sechdr;
	struct rxrpc_skb_priv *sp;
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv;
	struct scatterlist sg[16];
	struct sk_buff *trailer;
	u32 data_size, buf;
	u16 check;
	int nsg;

	_enter("");

	sp = rxrpc_skb(skb);

	/* we want to decrypt the skbuff in-place */
	nsg = skb_cow_data(skb, 0, &trailer);
	if (nsg < 0 || nsg > 16)
		goto nomem;

	sg_init_table(sg, nsg);
	skb_to_sgvec(skb, sg, 0, 8);

	/* start the decryption afresh */
	memset(&iv, 0, sizeof(iv));
	desc.tfm = call->conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	crypto_blkcipher_decrypt_iv(&desc, sg, sg, 8);

	/* remove the decrypted packet length */
	if (skb_copy_bits(skb, 0, &sechdr, sizeof(sechdr)) < 0)
		goto datalen_error;
	if (!skb_pull(skb, sizeof(sechdr)))
		BUG();

	buf = ntohl(sechdr.data_size);
	data_size = buf & 0xffff;

	check = buf >> 16;
	check ^= ntohl(sp->hdr.seq ^ sp->hdr.callNumber);
	check &= 0xffff;
	if (check != 0) {
		*_abort_code = RXKADSEALEDINCON;
		goto protocol_error;
	}

	/* shorten the packet to remove the padding */
	if (data_size > skb->len)
		goto datalen_error;
	else if (data_size < skb->len)
		skb->len = data_size;

	_leave(" = 0 [dlen=%x]", data_size);
	return 0;

datalen_error:
	*_abort_code = RXKADDATALEN;
protocol_error:
	_leave(" = -EPROTO");
	return -EPROTO;

nomem:
	_leave(" = -ENOMEM");
	return -ENOMEM;
}

/*
 * wholly decrypt a packet (level 2 security)
 */
static int rxkad_verify_packet_encrypt(const struct rxrpc_call *call,
				       struct sk_buff *skb,
				       u32 *_abort_code)
{
	const struct rxrpc_key_payload *payload;
	struct rxkad_level2_hdr sechdr;
	struct rxrpc_skb_priv *sp;
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv;
	struct scatterlist _sg[4], *sg;
	struct sk_buff *trailer;
	u32 data_size, buf;
	u16 check;
	int nsg;

	_enter(",{%d}", skb->len);

	sp = rxrpc_skb(skb);

	/* we want to decrypt the skbuff in-place */
	nsg = skb_cow_data(skb, 0, &trailer);
	if (nsg < 0)
		goto nomem;

	sg = _sg;
	if (unlikely(nsg > 4)) {
		sg = kmalloc(sizeof(*sg) * nsg, GFP_NOIO);
		if (!sg)
			goto nomem;
	}

	sg_init_table(sg, nsg);
	skb_to_sgvec(skb, sg, 0, skb->len);

	/* decrypt from the session key */
	payload = call->conn->key->payload.data;
	memcpy(&iv, payload->k.session_key, sizeof(iv));
	desc.tfm = call->conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	crypto_blkcipher_decrypt_iv(&desc, sg, sg, skb->len);
	if (sg != _sg)
		kfree(sg);

	/* remove the decrypted packet length */
	if (skb_copy_bits(skb, 0, &sechdr, sizeof(sechdr)) < 0)
		goto datalen_error;
	if (!skb_pull(skb, sizeof(sechdr)))
		BUG();

	buf = ntohl(sechdr.data_size);
	data_size = buf & 0xffff;

	check = buf >> 16;
	check ^= ntohl(sp->hdr.seq ^ sp->hdr.callNumber);
	check &= 0xffff;
	if (check != 0) {
		*_abort_code = RXKADSEALEDINCON;
		goto protocol_error;
	}

	/* shorten the packet to remove the padding */
	if (data_size > skb->len)
		goto datalen_error;
	else if (data_size < skb->len)
		skb->len = data_size;

	_leave(" = 0 [dlen=%x]", data_size);
	return 0;

datalen_error:
	*_abort_code = RXKADDATALEN;
protocol_error:
	_leave(" = -EPROTO");
	return -EPROTO;

nomem:
	_leave(" = -ENOMEM");
	return -ENOMEM;
}

/*
 * verify the security on a received packet
 */
static int rxkad_verify_packet(const struct rxrpc_call *call,
			       struct sk_buff *skb,
			       u32 *_abort_code)
{
	struct blkcipher_desc desc;
	struct rxrpc_skb_priv *sp;
	struct rxrpc_crypt iv;
	struct scatterlist sg[2];
	struct {
		__be32 x[2];
	} tmpbuf __attribute__((aligned(8))); /* must all be in same page */
	__be32 x;
	__be16 cksum;
	int ret;

	sp = rxrpc_skb(skb);

	_enter("{%d{%x}},{#%u}",
	       call->debug_id, key_serial(call->conn->key),
	       ntohl(sp->hdr.seq));

	if (!call->conn->cipher)
		return 0;

	if (sp->hdr.securityIndex != 2) {
		*_abort_code = RXKADINCONSISTENCY;
		_leave(" = -EPROTO [not rxkad]");
		return -EPROTO;
	}

	/* continue encrypting from where we left off */
	memcpy(&iv, call->conn->csum_iv.x, sizeof(iv));
	desc.tfm = call->conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	/* validate the security checksum */
	x = htonl(call->channel << (32 - RXRPC_CIDSHIFT));
	x |= sp->hdr.seq & cpu_to_be32(0x3fffffff);
	tmpbuf.x[0] = call->call_id;
	tmpbuf.x[1] = x;

	sg_init_one(&sg[0], &tmpbuf, sizeof(tmpbuf));
	sg_init_one(&sg[1], &tmpbuf, sizeof(tmpbuf));
	crypto_blkcipher_encrypt_iv(&desc, &sg[0], &sg[1], sizeof(tmpbuf));

	x = ntohl(tmpbuf.x[1]);
	x = (x >> 16) & 0xffff;
	if (x == 0)
		x = 1; /* zero checksums are not permitted */

	cksum = htons(x);
	if (sp->hdr.cksum != cksum) {
		*_abort_code = RXKADSEALEDINCON;
		_leave(" = -EPROTO [csum failed]");
		return -EPROTO;
	}

	switch (call->conn->security_level) {
	case RXRPC_SECURITY_PLAIN:
		ret = 0;
		break;
	case RXRPC_SECURITY_AUTH:
		ret = rxkad_verify_packet_auth(call, skb, _abort_code);
		break;
	case RXRPC_SECURITY_ENCRYPT:
		ret = rxkad_verify_packet_encrypt(call, skb, _abort_code);
		break;
	default:
		ret = -ENOANO;
		break;
	}

	_leave(" = %d", ret);
	return ret;
}

/*
 * issue a challenge
 */
static int rxkad_issue_challenge(struct rxrpc_connection *conn)
{
	struct rxkad_challenge challenge;
	struct rxrpc_header hdr;
	struct msghdr msg;
	struct kvec iov[2];
	size_t len;
	int ret;

	_enter("{%d,%x}", conn->debug_id, key_serial(conn->key));

	ret = key_validate(conn->key);
	if (ret < 0)
		return ret;

	get_random_bytes(&conn->security_nonce, sizeof(conn->security_nonce));

	challenge.version	= htonl(2);
	challenge.nonce		= htonl(conn->security_nonce);
	challenge.min_level	= htonl(0);
	challenge.__padding	= 0;

	msg.msg_name	= &conn->trans->peer->srx.transport.sin;
	msg.msg_namelen	= sizeof(conn->trans->peer->srx.transport.sin);
	msg.msg_control	= NULL;
	msg.msg_controllen = 0;
	msg.msg_flags	= 0;

	hdr.epoch	= conn->epoch;
	hdr.cid		= conn->cid;
	hdr.callNumber	= 0;
	hdr.seq		= 0;
	hdr.type	= RXRPC_PACKET_TYPE_CHALLENGE;
	hdr.flags	= conn->out_clientflag;
	hdr.userStatus	= 0;
	hdr.securityIndex = conn->security_ix;
	hdr._rsvd	= 0;
	hdr.serviceId	= conn->service_id;

	iov[0].iov_base	= &hdr;
	iov[0].iov_len	= sizeof(hdr);
	iov[1].iov_base	= &challenge;
	iov[1].iov_len	= sizeof(challenge);

	len = iov[0].iov_len + iov[1].iov_len;

	hdr.serial = htonl(atomic_inc_return(&conn->serial));
	_proto("Tx CHALLENGE %%%u", ntohl(hdr.serial));

	ret = kernel_sendmsg(conn->trans->local->socket, &msg, iov, 2, len);
	if (ret < 0) {
		_debug("sendmsg failed: %d", ret);
		return -EAGAIN;
	}

	_leave(" = 0");
	return 0;
}

/*
 * send a Kerberos security response
 */
static int rxkad_send_response(struct rxrpc_connection *conn,
			       struct rxrpc_header *hdr,
			       struct rxkad_response *resp,
			       const struct rxkad_key *s2)
{
	struct msghdr msg;
	struct kvec iov[3];
	size_t len;
	int ret;

	_enter("");

	msg.msg_name	= &conn->trans->peer->srx.transport.sin;
	msg.msg_namelen	= sizeof(conn->trans->peer->srx.transport.sin);
	msg.msg_control	= NULL;
	msg.msg_controllen = 0;
	msg.msg_flags	= 0;

	hdr->epoch	= conn->epoch;
	hdr->seq	= 0;
	hdr->type	= RXRPC_PACKET_TYPE_RESPONSE;
	hdr->flags	= conn->out_clientflag;
	hdr->userStatus	= 0;
	hdr->_rsvd	= 0;

	iov[0].iov_base	= hdr;
	iov[0].iov_len	= sizeof(*hdr);
	iov[1].iov_base	= resp;
	iov[1].iov_len	= sizeof(*resp);
	iov[2].iov_base	= (void *) s2->ticket;
	iov[2].iov_len	= s2->ticket_len;

	len = iov[0].iov_len + iov[1].iov_len + iov[2].iov_len;

	hdr->serial = htonl(atomic_inc_return(&conn->serial));
	_proto("Tx RESPONSE %%%u", ntohl(hdr->serial));

	ret = kernel_sendmsg(conn->trans->local->socket, &msg, iov, 3, len);
	if (ret < 0) {
		_debug("sendmsg failed: %d", ret);
		return -EAGAIN;
	}

	_leave(" = 0");
	return 0;
}

/*
 * calculate the response checksum
 */
static void rxkad_calc_response_checksum(struct rxkad_response *response)
{
	u32 csum = 1000003;
	int loop;
	u8 *p = (u8 *) response;

	for (loop = sizeof(*response); loop > 0; loop--)
		csum = csum * 0x10204081 + *p++;

	response->encrypted.checksum = htonl(csum);
}

/*
 * load a scatterlist with a potentially split-page buffer
 */
static void rxkad_sg_set_buf2(struct scatterlist sg[2],
			      void *buf, size_t buflen)
{
	int nsg = 1;

	sg_init_table(sg, 2);

	sg_set_buf(&sg[0], buf, buflen);
	if (sg[0].offset + buflen > PAGE_SIZE) {
		/* the buffer was split over two pages */
		sg[0].length = PAGE_SIZE - sg[0].offset;
		sg_set_buf(&sg[1], buf + sg[0].length, buflen - sg[0].length);
		nsg++;
	}

	sg_mark_end(&sg[nsg - 1]);

	ASSERTCMP(sg[0].length + sg[1].length, ==, buflen);
}

/*
 * encrypt the response packet
 */
static void rxkad_encrypt_response(struct rxrpc_connection *conn,
				   struct rxkad_response *resp,
				   const struct rxkad_key *s2)
{
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv;
	struct scatterlist sg[2];

	/* continue encrypting from where we left off */
	memcpy(&iv, s2->session_key, sizeof(iv));
	desc.tfm = conn->cipher;
	desc.info = iv.x;
	desc.flags = 0;

	rxkad_sg_set_buf2(sg, &resp->encrypted, sizeof(resp->encrypted));
	crypto_blkcipher_encrypt_iv(&desc, sg, sg, sizeof(resp->encrypted));
}

/*
 * respond to a challenge packet
 */
static int rxkad_respond_to_challenge(struct rxrpc_connection *conn,
				      struct sk_buff *skb,
				      u32 *_abort_code)
{
	const struct rxrpc_key_payload *payload;
	struct rxkad_challenge challenge;
	struct rxkad_response resp
		__attribute__((aligned(8))); /* must be aligned for crypto */
	struct rxrpc_skb_priv *sp;
	u32 version, nonce, min_level, abort_code;
	int ret;

	_enter("{%d,%x}", conn->debug_id, key_serial(conn->key));

	if (!conn->key) {
		_leave(" = -EPROTO [no key]");
		return -EPROTO;
	}

	ret = key_validate(conn->key);
	if (ret < 0) {
		*_abort_code = RXKADEXPIRED;
		return ret;
	}

	abort_code = RXKADPACKETSHORT;
	sp = rxrpc_skb(skb);
	if (skb_copy_bits(skb, 0, &challenge, sizeof(challenge)) < 0)
		goto protocol_error;

	version = ntohl(challenge.version);
	nonce = ntohl(challenge.nonce);
	min_level = ntohl(challenge.min_level);

	_proto("Rx CHALLENGE %%%u { v=%u n=%u ml=%u }",
	       ntohl(sp->hdr.serial), version, nonce, min_level);

	abort_code = RXKADINCONSISTENCY;
	if (version != RXKAD_VERSION)
		goto protocol_error;

	abort_code = RXKADLEVELFAIL;
	if (conn->security_level < min_level)
		goto protocol_error;

	payload = conn->key->payload.data;

	/* build the response packet */
	memset(&resp, 0, sizeof(resp));

	resp.version = RXKAD_VERSION;
	resp.encrypted.epoch = conn->epoch;
	resp.encrypted.cid = conn->cid;
	resp.encrypted.securityIndex = htonl(conn->security_ix);
	resp.encrypted.call_id[0] =
		(conn->channels[0] ? conn->channels[0]->call_id : 0);
	resp.encrypted.call_id[1] =
		(conn->channels[1] ? conn->channels[1]->call_id : 0);
	resp.encrypted.call_id[2] =
		(conn->channels[2] ? conn->channels[2]->call_id : 0);
	resp.encrypted.call_id[3] =
		(conn->channels[3] ? conn->channels[3]->call_id : 0);
	resp.encrypted.inc_nonce = htonl(nonce + 1);
	resp.encrypted.level = htonl(conn->security_level);
	resp.kvno = htonl(payload->k.kvno);
	resp.ticket_len = htonl(payload->k.ticket_len);

	/* calculate the response checksum and then do the encryption */
	rxkad_calc_response_checksum(&resp);
	rxkad_encrypt_response(conn, &resp, &payload->k);
	return rxkad_send_response(conn, &sp->hdr, &resp, &payload->k);

protocol_error:
	*_abort_code = abort_code;
	_leave(" = -EPROTO [%d]", abort_code);
	return -EPROTO;
}

/*
 * decrypt the kerberos IV ticket in the response
 */
static int rxkad_decrypt_ticket(struct rxrpc_connection *conn,
				void *ticket, size_t ticket_len,
				struct rxrpc_crypt *_session_key,
				time_t *_expiry,
				u32 *_abort_code)
{
	struct blkcipher_desc desc;
	struct rxrpc_crypt iv, key;
	struct scatterlist sg[1];
	struct in_addr addr;
	unsigned life;
	time_t issue, now;
	bool little_endian;
	int ret;
	u8 *p, *q, *name, *end;

	_enter("{%d},{%x}", conn->debug_id, key_serial(conn->server_key));

	*_expiry = 0;

	ret = key_validate(conn->server_key);
	if (ret < 0) {
		switch (ret) {
		case -EKEYEXPIRED:
			*_abort_code = RXKADEXPIRED;
			goto error;
		default:
			*_abort_code = RXKADNOAUTH;
			goto error;
		}
	}

	ASSERT(conn->server_key->payload.data != NULL);
	ASSERTCMP((unsigned long) ticket & 7UL, ==, 0);

	memcpy(&iv, &conn->server_key->type_data, sizeof(iv));

	desc.tfm = conn->server_key->payload.data;
	desc.info = iv.x;
	desc.flags = 0;

	sg_init_one(&sg[0], ticket, ticket_len);
	crypto_blkcipher_decrypt_iv(&desc, sg, sg, ticket_len);

	p = ticket;
	end = p + ticket_len;

#define Z(size)						\
	({						\
		u8 *__str = p;				\
		q = memchr(p, 0, end - p);		\
		if (!q || q - p > (size))		\
			goto bad_ticket;		\
		for (; p < q; p++)			\
			if (!isprint(*p))		\
				goto bad_ticket;	\
		p++;					\
		__str;					\
	})

	/* extract the ticket flags */
	_debug("KIV FLAGS: %x", *p);
	little_endian = *p & 1;
	p++;

	/* extract the authentication name */
	name = Z(ANAME_SZ);
	_debug("KIV ANAME: %s", name);

	/* extract the principal's instance */
	name = Z(INST_SZ);
	_debug("KIV INST : %s", name);

	/* extract the principal's authentication domain */
	name = Z(REALM_SZ);
	_debug("KIV REALM: %s", name);

	if (end - p < 4 + 8 + 4 + 2)
		goto bad_ticket;

	/* get the IPv4 address of the entity that requested the ticket */
	memcpy(&addr, p, sizeof(addr));
	p += 4;
	_debug("KIV ADDR : "NIPQUAD_FMT, NIPQUAD(addr));

	/* get the session key from the ticket */
	memcpy(&key, p, sizeof(key));
	p += 8;
	_debug("KIV KEY  : %08x %08x", ntohl(key.n[0]), ntohl(key.n[1]));
	memcpy(_session_key, &key, sizeof(key));

	/* get the ticket's lifetime */
	life = *p++ * 5 * 60;
	_debug("KIV LIFE : %u", life);

	/* get the issue time of the ticket */
	if (little_endian) {
		__le32 stamp;
		memcpy(&stamp, p, 4);
		issue = le32_to_cpu(stamp);
	} else {
		__be32 stamp;
		memcpy(&stamp, p, 4);
		issue = be32_to_cpu(stamp);
	}
	p += 4;
	now = get_seconds();
	_debug("KIV ISSUE: %lx [%lx]", issue, now);

	/* check the ticket is in date */
	if (issue > now) {
		*_abort_code = RXKADNOAUTH;
		ret = -EKEYREJECTED;
		goto error;
	}

	if (issue < now - life) {
		*_abort_code = RXKADEXPIRED;
		ret = -EKEYEXPIRED;
		goto error;
	}

	*_expiry = issue + life;

	/* get the service name */
	name = Z(SNAME_SZ);
	_debug("KIV SNAME: %s", name);

	/* get the service instance name */
	name = Z(INST_SZ);
	_debug("KIV SINST: %s", name);

	ret = 0;
error:
	_leave(" = %d", ret);
	return ret;

bad_ticket:
	*_abort_code = RXKADBADTICKET;
	ret = -EBADMSG;
	goto error;
}

/*
 * decrypt the response packet
 */
static void rxkad_decrypt_response(struct rxrpc_connection *conn,
				   struct rxkad_response *resp,
				   const struct rxrpc_crypt *session_key)
{
	struct blkcipher_desc desc;
	struct scatterlist sg[2];
	struct rxrpc_crypt iv;

	_enter(",,%08x%08x",
	       ntohl(session_key->n[0]), ntohl(session_key->n[1]));

	ASSERT(rxkad_ci != NULL);

	mutex_lock(&rxkad_ci_mutex);
	if (crypto_blkcipher_setkey(rxkad_ci, session_key->x,
				    sizeof(*session_key)) < 0)
		BUG();

	memcpy(&iv, session_key, sizeof(iv));
	desc.tfm = rxkad_ci;
	desc.info = iv.x;
	desc.flags = 0;

	rxkad_sg_set_buf2(sg, &resp->encrypted, sizeof(resp->encrypted));
	crypto_blkcipher_decrypt_iv(&desc, sg, sg, sizeof(resp->encrypted));
	mutex_unlock(&rxkad_ci_mutex);

	_leave("");
}

/*
 * verify a response
 */
static int rxkad_verify_response(struct rxrpc_connection *conn,
				 struct sk_buff *skb,
				 u32 *_abort_code)
{
	struct rxkad_response response
		__attribute__((aligned(8))); /* must be aligned for crypto */
	struct rxrpc_skb_priv *sp;
	struct rxrpc_crypt session_key;
	time_t expiry;
	void *ticket;
	u32 abort_code, version, kvno, ticket_len, csum, level;
	int ret;

	_enter("{%d,%x}", conn->debug_id, key_serial(conn->server_key));

	abort_code = RXKADPACKETSHORT;
	if (skb_copy_bits(skb, 0, &response, sizeof(response)) < 0)
		goto protocol_error;
	if (!pskb_pull(skb, sizeof(response)))
		BUG();

	version = ntohl(response.version);
	ticket_len = ntohl(response.ticket_len);
	kvno = ntohl(response.kvno);
	sp = rxrpc_skb(skb);
	_proto("Rx RESPONSE %%%u { v=%u kv=%u tl=%u }",
	       ntohl(sp->hdr.serial), version, kvno, ticket_len);

	abort_code = RXKADINCONSISTENCY;
	if (version != RXKAD_VERSION)
		goto protocol_error;

	abort_code = RXKADTICKETLEN;
	if (ticket_len < 4 || ticket_len > MAXKRB5TICKETLEN)
		goto protocol_error;

	abort_code = RXKADUNKNOWNKEY;
	if (kvno >= RXKAD_TKT_TYPE_KERBEROS_V5)
		goto protocol_error;

	/* extract the kerberos ticket and decrypt and decode it */
	ticket = kmalloc(ticket_len, GFP_NOFS);
	if (!ticket)
		return -ENOMEM;

	abort_code = RXKADPACKETSHORT;
	if (skb_copy_bits(skb, 0, ticket, ticket_len) < 0)
		goto protocol_error_free;

	ret = rxkad_decrypt_ticket(conn, ticket, ticket_len, &session_key,
				   &expiry, &abort_code);
	if (ret < 0) {
		*_abort_code = abort_code;
		kfree(ticket);
		return ret;
	}

	/* use the session key from inside the ticket to decrypt the
	 * response */
	rxkad_decrypt_response(conn, &response, &session_key);

	abort_code = RXKADSEALEDINCON;
	if (response.encrypted.epoch != conn->epoch)
		goto protocol_error_free;
	if (response.encrypted.cid != conn->cid)
		goto protocol_error_free;
	if (ntohl(response.encrypted.securityIndex) != conn->security_ix)
		goto protocol_error_free;
	csum = response.encrypted.checksum;
	response.encrypted.checksum = 0;
	rxkad_calc_response_checksum(&response);
	if (response.encrypted.checksum != csum)
		goto protocol_error_free;

	if (ntohl(response.encrypted.call_id[0]) > INT_MAX ||
	    ntohl(response.encrypted.call_id[1]) > INT_MAX ||
	    ntohl(response.encrypted.call_id[2]) > INT_MAX ||
	    ntohl(response.encrypted.call_id[3]) > INT_MAX)
		goto protocol_error_free;

	abort_code = RXKADOUTOFSEQUENCE;
	if (response.encrypted.inc_nonce != htonl(conn->security_nonce + 1))
		goto protocol_error_free;

	abort_code = RXKADLEVELFAIL;
	level = ntohl(response.encrypted.level);
	if (level > RXRPC_SECURITY_ENCRYPT)
		goto protocol_error_free;
	conn->security_level = level;

	/* create a key to hold the security data and expiration time - after
	 * this the connection security can be handled in exactly the same way
	 * as for a client connection */
	ret = rxrpc_get_server_data_key(conn, &session_key, expiry, kvno);
	if (ret < 0) {
		kfree(ticket);
		return ret;
	}

	kfree(ticket);
	_leave(" = 0");
	return 0;

protocol_error_free:
	kfree(ticket);
protocol_error:
	*_abort_code = abort_code;
	_leave(" = -EPROTO [%d]", abort_code);
	return -EPROTO;
}

/*
 * clear the connection security
 */
static void rxkad_clear(struct rxrpc_connection *conn)
{
	_enter("");

	if (conn->cipher)
		crypto_free_blkcipher(conn->cipher);
}

/*
 * RxRPC Kerberos-based security
 */
static struct rxrpc_security rxkad = {
	.owner				= THIS_MODULE,
	.name				= "rxkad",
	.security_index			= RXKAD_VERSION,
	.init_connection_security	= rxkad_init_connection_security,
	.prime_packet_security		= rxkad_prime_packet_security,
	.secure_packet			= rxkad_secure_packet,
	.verify_packet			= rxkad_verify_packet,
	.issue_challenge		= rxkad_issue_challenge,
	.respond_to_challenge		= rxkad_respond_to_challenge,
	.verify_response		= rxkad_verify_response,
	.clear				= rxkad_clear,
};

static __init int rxkad_init(void)
{
	_enter("");

	/* pin the cipher we need so that the crypto layer doesn't invoke
	 * keventd to go get it */
	rxkad_ci = crypto_alloc_blkcipher("pcbc(fcrypt)", 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(rxkad_ci))
		return PTR_ERR(rxkad_ci);

	return rxrpc_register_security(&rxkad);
}

module_init(rxkad_init);

static __exit void rxkad_exit(void)
{
	_enter("");

	rxrpc_unregister_security(&rxkad);
	crypto_free_blkcipher(rxkad_ci);
}

module_exit(rxkad_exit);