[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both

Provide AF_RXRPC sockets that can be used to talk to AFS servers, or serve
answers to AFS clients.  KerberosIV security is fully supported.  The patches
and some example test programs can be found in:

	http://people.redhat.com/~dhowells/rxrpc/

This will eventually replace the old implementation of kernel-only RxRPC
currently resident in net/rxrpc/.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1153 insertions, 0 deletions

diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
new file mode 100644
index 00000000000..1eaf529efac
--- /dev/null
+++ b/net/rxrpc/rxkad.c
@@ -0,0 +1,1153 @@
+/* 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>
+#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);
+
+	memset(sg, 0, sizeof(sg));
+	sg_set_buf(&sg[0], &tmpbuf, sizeof(tmpbuf));
+	sg_set_buf(&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;
+
+	memset(sg, 0, sizeof(sg));
+	sg_set_buf(&sg[0], &tmpbuf, sizeof(tmpbuf));
+	sg_set_buf(&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;
+
+	memset(sg, 0, sizeof(sg[0]) * 2);
+	sg_set_buf(&sg[0], sechdr, sizeof(rxkhdr));
+	sg_set_buf(&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);
+
+	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 & __constant_cpu_to_be32(0x3fffffff);
+	tmpbuf.x[0] = sp->hdr.callNumber;
+	tmpbuf.x[1] = x;
+
+	memset(&sg, 0, sizeof(sg));
+	sg_set_buf(&sg[0], &tmpbuf, sizeof(tmpbuf));
+	sg_set_buf(&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[2];
+	struct sk_buff *trailer;
+	u32 data_size, buf;
+	u16 check;
+
+	_enter("");
+
+	sp = rxrpc_skb(skb);
+
+	/* we want to decrypt the skbuff in-place */
+	if (skb_cow_data(skb, 0, &trailer) < 0)
+		goto nomem;
+
+	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;
+	}
+
+	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 & __constant_cpu_to_be32(0x3fffffff);
+	tmpbuf.x[0] = call->call_id;
+	tmpbuf.x[1] = x;
+
+	memset(&sg, 0, sizeof(sg));
+	sg_set_buf(&sg[0], &tmpbuf, sizeof(tmpbuf));
+	sg_set_buf(&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)
+{
+
+	memset(sg, 0, sizeof(sg));
+
+	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);
+	}
+
+	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 ssg[2], dsg[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(ssg, &resp->encrypted, sizeof(resp->encrypted));
+	memcpy(dsg, ssg, sizeof(dsg));
+	crypto_blkcipher_encrypt_iv(&desc, dsg, ssg, 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 ssg[1], dsg[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(&ssg[0], ticket, ticket_len);
+	memcpy(dsg, ssg, sizeof(dsg));
+	crypto_blkcipher_decrypt_iv(&desc, dsg, ssg, 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 = xtime.tv_sec;
+	_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 ssg[2], dsg[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(ssg, &resp->encrypted, sizeof(resp->encrypted));
+	memcpy(dsg, ssg, sizeof(dsg));
+	crypto_blkcipher_decrypt_iv(&desc, dsg, ssg, 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)
+
+	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);