/* 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(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;
        u32 y;
        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));

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

        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, y);
        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;
        u32 y;
        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));

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

        cksum = htons(y);
        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, level;
        __be32 csum;
        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);