// SPDX-License-Identifier: GPL-2.0-or-later
/* Kerberos-based RxRPC security
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <crypto/skcipher.h>
#include <linux/module.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/udp.h>
#include <linux/scatterlist.h>
#include <linux/ctype.h>
#include <linux/slab.h>
#include <linux/key-type.h>
#include <net/sock.h>
#include <net/af_rxrpc.h>
#include <keys/rxrpc-type.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 */
#define RXKAD_ALIGN                     8

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 */
};

static int rxkad_prime_packet_security(struct rxrpc_connection *conn,
                                       struct crypto_sync_skcipher *ci);

/*
 * 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_sync_skcipher *rxkad_ci;
static struct skcipher_request *rxkad_ci_req;
static DEFINE_MUTEX(rxkad_ci_mutex);

/*
 * Parse the information from a server key
 *
 * The data should be the 8-byte secret key.
 */
static int rxkad_preparse_server_key(struct key_preparsed_payload *prep)
{
        struct crypto_skcipher *ci;

        if (prep->datalen != 8)
                return -EINVAL;

        memcpy(&prep->payload.data[2], prep->data, 8);

        ci = crypto_alloc_skcipher("pcbc(des)", 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(ci)) {
                _leave(" = %ld", PTR_ERR(ci));
                return PTR_ERR(ci);
        }

        if (crypto_skcipher_setkey(ci, prep->data, 8) < 0)
                BUG();

        prep->payload.data[0] = ci;
        _leave(" = 0");
        return 0;
}

static void rxkad_free_preparse_server_key(struct key_preparsed_payload *prep)
{

        if (prep->payload.data[0])
                crypto_free_skcipher(prep->payload.data[0]);
}

static void rxkad_destroy_server_key(struct key *key)
{
        if (key->payload.data[0]) {
                crypto_free_skcipher(key->payload.data[0]);
                key->payload.data[0] = NULL;
        }
}

/*
 * initialise connection security
 */
static int rxkad_init_connection_security(struct rxrpc_connection *conn,
                                          struct rxrpc_key_token *token)
{
        struct crypto_sync_skcipher *ci;
        int ret;

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

        conn->security_ix = token->security_index;

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

        if (crypto_sync_skcipher_setkey(ci, token->kad->session_key,
                                   sizeof(token->kad->session_key)) < 0)
                BUG();

        switch (conn->security_level) {
        case RXRPC_SECURITY_PLAIN:
        case RXRPC_SECURITY_AUTH:
        case RXRPC_SECURITY_ENCRYPT:
                break;
        default:
                ret = -EKEYREJECTED;
                goto error;
        }

        ret = rxkad_prime_packet_security(conn, ci);
        if (ret < 0)
                goto error_ci;

        conn->rxkad.cipher = ci;
        return 0;

error_ci:
        crypto_free_sync_skcipher(ci);
error:
        _leave(" = %d", ret);
        return ret;
}

/*
 * Work out how much data we can put in a packet.
 */
static struct rxrpc_txbuf *rxkad_alloc_txbuf(struct rxrpc_call *call, size_t remain, gfp_t gfp)
{
        struct rxrpc_txbuf *txb;
        size_t shdr, alloc, limit, part;

        remain = umin(remain, 65535 - sizeof(struct rxrpc_wire_header));

        switch (call->conn->security_level) {
        default:
                alloc = umin(remain, RXRPC_JUMBO_DATALEN);
                return rxrpc_alloc_data_txbuf(call, alloc, 1, gfp);
        case RXRPC_SECURITY_AUTH:
                shdr = sizeof(struct rxkad_level1_hdr);
                break;
        case RXRPC_SECURITY_ENCRYPT:
                shdr = sizeof(struct rxkad_level2_hdr);
                break;
        }

        limit = round_down(RXRPC_JUMBO_DATALEN, RXKAD_ALIGN) - shdr;
        if (remain < limit) {
                part = remain;
                alloc = round_up(shdr + part, RXKAD_ALIGN);
        } else {
                part = limit;
                alloc = RXRPC_JUMBO_DATALEN;
        }

        txb = rxrpc_alloc_data_txbuf(call, alloc, RXKAD_ALIGN, gfp);
        if (!txb)
                return NULL;

        txb->crypto_header      = 0;
        txb->sec_header         = shdr;
        txb->offset             += shdr;
        txb->space              = part;
        return txb;
}

/*
 * prime the encryption state with the invariant parts of a connection's
 * description
 */
static int rxkad_prime_packet_security(struct rxrpc_connection *conn,
                                       struct crypto_sync_skcipher *ci)
{
        struct skcipher_request *req;
        struct rxrpc_key_token *token;
        struct scatterlist sg;
        struct rxrpc_crypt iv;
        __be32 *tmpbuf;
        size_t tmpsize = 4 * sizeof(__be32);

        _enter("");

        if (!conn->key)
                return 0;

        tmpbuf = kmalloc(tmpsize, GFP_KERNEL);
        if (!tmpbuf)
                return -ENOMEM;

        req = skcipher_request_alloc(&ci->base, GFP_NOFS);
        if (!req) {
                kfree(tmpbuf);
                return -ENOMEM;
        }

        token = conn->key->payload.data[0];
        memcpy(&iv, token->kad->session_key, sizeof(iv));

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

        sg_init_one(&sg, tmpbuf, tmpsize);
        skcipher_request_set_sync_tfm(req, ci);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, &sg, &sg, tmpsize, iv.x);
        crypto_skcipher_encrypt(req);
        skcipher_request_free(req);

        memcpy(&conn->rxkad.csum_iv, tmpbuf + 2, sizeof(conn->rxkad.csum_iv));
        kfree(tmpbuf);
        _leave(" = 0");
        return 0;
}

/*
 * Allocate and prepare the crypto request on a call.  For any particular call,
 * this is called serially for the packets, so no lock should be necessary.
 */
static struct skcipher_request *rxkad_get_call_crypto(struct rxrpc_call *call)
{
        struct crypto_skcipher *tfm = &call->conn->rxkad.cipher->base;

        return skcipher_request_alloc(tfm, GFP_NOFS);
}

/*
 * Clean up the crypto on a call.
 */
static void rxkad_free_call_crypto(struct rxrpc_call *call)
{
}

/*
 * partially encrypt a packet (level 1 security)
 */
static int rxkad_secure_packet_auth(const struct rxrpc_call *call,
                                    struct rxrpc_txbuf *txb,
                                    struct skcipher_request *req)
{
        struct rxkad_level1_hdr *hdr = txb->data;
        struct rxrpc_crypt iv;
        struct scatterlist sg;
        size_t pad;
        u16 check;

        _enter("");

        check = txb->seq ^ call->call_id;
        hdr->data_size = htonl((u32)check << 16 | txb->len);

        txb->pkt_len = sizeof(struct rxkad_level1_hdr) + txb->len;
        pad = txb->pkt_len;
        pad = RXKAD_ALIGN - pad;
        pad &= RXKAD_ALIGN - 1;
        if (pad) {
                memset(txb->data + txb->offset, 0, pad);
                txb->pkt_len += pad;
        }

        /* start the encryption afresh */
        memset(&iv, 0, sizeof(iv));

        sg_init_one(&sg, hdr, 8);
        skcipher_request_set_sync_tfm(req, call->conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, &sg, &sg, 8, iv.x);
        crypto_skcipher_encrypt(req);
        skcipher_request_zero(req);

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

/*
 * wholly encrypt a packet (level 2 security)
 */
static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call,
                                       struct rxrpc_txbuf *txb,
                                       struct skcipher_request *req)
{
        const struct rxrpc_key_token *token;
        struct rxkad_level2_hdr *rxkhdr = txb->data;
        struct rxrpc_crypt iv;
        struct scatterlist sg;
        size_t content, pad;
        u16 check;
        int ret;

        _enter("");

        check = txb->seq ^ call->call_id;

        rxkhdr->data_size = htonl(txb->len | (u32)check << 16);
        rxkhdr->checksum = 0;

        content = sizeof(struct rxkad_level2_hdr) + txb->len;
        txb->pkt_len = round_up(content, RXKAD_ALIGN);
        pad = txb->pkt_len - content;
        if (pad)
                memset(txb->data + txb->offset, 0, pad);

        /* encrypt from the session key */
        token = call->conn->key->payload.data[0];
        memcpy(&iv, token->kad->session_key, sizeof(iv));

        sg_init_one(&sg, rxkhdr, txb->pkt_len);
        skcipher_request_set_sync_tfm(req, call->conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, &sg, &sg, txb->pkt_len, iv.x);
        ret = crypto_skcipher_encrypt(req);
        skcipher_request_zero(req);
        return ret;
}

/*
 * checksum an RxRPC packet header
 */
static int rxkad_secure_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
{
        struct skcipher_request *req;
        struct rxrpc_crypt iv;
        struct scatterlist sg;
        union {
                __be32 buf[2];
        } crypto __aligned(8);
        u32 x, y;
        int ret;

        _enter("{%d{%x}},{#%u},%u,",
               call->debug_id, key_serial(call->conn->key),
               txb->seq, txb->len);

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

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

        req = rxkad_get_call_crypto(call);
        if (!req)
                return -ENOMEM;

        /* continue encrypting from where we left off */
        memcpy(&iv, call->conn->rxkad.csum_iv.x, sizeof(iv));

        /* calculate the security checksum */
        x = (call->cid & RXRPC_CHANNELMASK) << (32 - RXRPC_CIDSHIFT);
        x |= txb->seq & 0x3fffffff;
        crypto.buf[0] = htonl(call->call_id);
        crypto.buf[1] = htonl(x);

        sg_init_one(&sg, crypto.buf, 8);
        skcipher_request_set_sync_tfm(req, call->conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, &sg, &sg, 8, iv.x);
        crypto_skcipher_encrypt(req);
        skcipher_request_zero(req);

        y = ntohl(crypto.buf[1]);
        y = (y >> 16) & 0xffff;
        if (y == 0)
                y = 1; /* zero checksums are not permitted */
        txb->cksum = htons(y);

        switch (call->conn->security_level) {
        case RXRPC_SECURITY_PLAIN:
                txb->pkt_len = txb->len;
                ret = 0;
                break;
        case RXRPC_SECURITY_AUTH:
                ret = rxkad_secure_packet_auth(call, txb, req);
                if (txb->alloc_size == RXRPC_JUMBO_DATALEN)
                        txb->jumboable = true;
                break;
        case RXRPC_SECURITY_ENCRYPT:
                ret = rxkad_secure_packet_encrypt(call, txb, req);
                if (txb->alloc_size == RXRPC_JUMBO_DATALEN)
                        txb->jumboable = true;
                break;
        default:
                ret = -EPERM;
                break;
        }

        /* Clear excess space in the packet */
        if (txb->pkt_len < txb->alloc_size) {
                size_t gap = txb->alloc_size - txb->pkt_len;
                void *p = txb->data;

                memset(p + txb->pkt_len, 0, gap);
        }

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

/*
 * decrypt partial encryption on a packet (level 1 security)
 */
static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
                                 rxrpc_seq_t seq,
                                 struct skcipher_request *req)
{
        struct rxkad_level1_hdr sechdr;
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        struct rxrpc_crypt iv;
        struct scatterlist sg[16];
        u32 data_size, buf;
        u16 check;
        int ret;

        _enter("");

        if (sp->len < 8)
                return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
                                          rxkad_abort_1_short_header);

        /* Decrypt the skbuff in-place.  TODO: We really want to decrypt
         * directly into the target buffer.
         */
        sg_init_table(sg, ARRAY_SIZE(sg));
        ret = skb_to_sgvec(skb, sg, sp->offset, 8);
        if (unlikely(ret < 0))
                return ret;

        /* start the decryption afresh */
        memset(&iv, 0, sizeof(iv));

        skcipher_request_set_sync_tfm(req, call->conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, sg, sg, 8, iv.x);
        crypto_skcipher_decrypt(req);
        skcipher_request_zero(req);

        /* Extract the decrypted packet length */
        if (skb_copy_bits(skb, sp->offset, &sechdr, sizeof(sechdr)) < 0)
                return rxrpc_abort_eproto(call, skb, RXKADDATALEN,
                                          rxkad_abort_1_short_encdata);
        sp->offset += sizeof(sechdr);
        sp->len    -= sizeof(sechdr);

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

        check = buf >> 16;
        check ^= seq ^ call->call_id;
        check &= 0xffff;
        if (check != 0)
                return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
                                          rxkad_abort_1_short_check);
        if (data_size > sp->len)
                return rxrpc_abort_eproto(call, skb, RXKADDATALEN,
                                          rxkad_abort_1_short_data);
        sp->len = data_size;

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

/*
 * wholly decrypt a packet (level 2 security)
 */
static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
                                 rxrpc_seq_t seq,
                                 struct skcipher_request *req)
{
        const struct rxrpc_key_token *token;
        struct rxkad_level2_hdr sechdr;
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        struct rxrpc_crypt iv;
        struct scatterlist _sg[4], *sg;
        u32 data_size, buf;
        u16 check;
        int nsg, ret;

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

        if (sp->len < 8)
                return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
                                          rxkad_abort_2_short_header);

        /* Decrypt the skbuff in-place.  TODO: We really want to decrypt
         * directly into the target buffer.
         */
        sg = _sg;
        nsg = skb_shinfo(skb)->nr_frags + 1;
        if (nsg <= 4) {
                nsg = 4;
        } else {
                sg = kmalloc_objs(*sg, nsg, GFP_NOIO);
                if (!sg)
                        return -ENOMEM;
        }

        sg_init_table(sg, nsg);
        ret = skb_to_sgvec(skb, sg, sp->offset, sp->len);
        if (unlikely(ret < 0)) {
                if (sg != _sg)
                        kfree(sg);
                return ret;
        }

        /* decrypt from the session key */
        token = call->conn->key->payload.data[0];
        memcpy(&iv, token->kad->session_key, sizeof(iv));

        skcipher_request_set_sync_tfm(req, call->conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, sg, sg, sp->len, iv.x);
        crypto_skcipher_decrypt(req);
        skcipher_request_zero(req);
        if (sg != _sg)
                kfree(sg);

        /* Extract the decrypted packet length */
        if (skb_copy_bits(skb, sp->offset, &sechdr, sizeof(sechdr)) < 0)
                return rxrpc_abort_eproto(call, skb, RXKADDATALEN,
                                          rxkad_abort_2_short_len);
        sp->offset += sizeof(sechdr);
        sp->len    -= sizeof(sechdr);

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

        check = buf >> 16;
        check ^= seq ^ call->call_id;
        check &= 0xffff;
        if (check != 0)
                return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
                                          rxkad_abort_2_short_check);

        if (data_size > sp->len)
                return rxrpc_abort_eproto(call, skb, RXKADDATALEN,
                                          rxkad_abort_2_short_data);

        sp->len = data_size;
        _leave(" = 0 [dlen=%x]", data_size);
        return 0;
}

/*
 * Verify the security on a received packet and the subpackets therein.
 */
static int rxkad_verify_packet(struct rxrpc_call *call, struct sk_buff *skb)
{
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        struct skcipher_request *req;
        struct rxrpc_crypt iv;
        struct scatterlist sg;
        union {
                __be32 buf[2];
        } crypto __aligned(8);
        rxrpc_seq_t seq = sp->hdr.seq;
        int ret;
        u16 cksum;
        u32 x, y;

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

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

        req = rxkad_get_call_crypto(call);
        if (!req)
                return -ENOMEM;

        /* continue encrypting from where we left off */
        memcpy(&iv, call->conn->rxkad.csum_iv.x, sizeof(iv));

        /* validate the security checksum */
        x = (call->cid & RXRPC_CHANNELMASK) << (32 - RXRPC_CIDSHIFT);
        x |= seq & 0x3fffffff;
        crypto.buf[0] = htonl(call->call_id);
        crypto.buf[1] = htonl(x);

        sg_init_one(&sg, crypto.buf, 8);
        skcipher_request_set_sync_tfm(req, call->conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, &sg, &sg, 8, iv.x);
        crypto_skcipher_encrypt(req);
        skcipher_request_zero(req);

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

        if (cksum != sp->hdr.cksum) {
                ret = rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
                                         rxkad_abort_bad_checksum);
                goto out;
        }

        switch (call->conn->security_level) {
        case RXRPC_SECURITY_PLAIN:
                ret = 0;
                break;
        case RXRPC_SECURITY_AUTH:
                ret = rxkad_verify_packet_1(call, skb, seq, req);
                break;
        case RXRPC_SECURITY_ENCRYPT:
                ret = rxkad_verify_packet_2(call, skb, seq, req);
                break;
        default:
                ret = -ENOANO;
                break;
        }

out:
        skcipher_request_free(req);
        return ret;
}

/*
 * issue a challenge
 */
static int rxkad_issue_challenge(struct rxrpc_connection *conn)
{
        struct rxkad_challenge challenge;
        struct rxrpc_wire_header whdr;
        struct msghdr msg;
        struct kvec iov[2];
        size_t len;
        u32 serial;
        int ret;

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

        get_random_bytes(&conn->rxkad.nonce, sizeof(conn->rxkad.nonce));

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

        msg.msg_name    = &conn->peer->srx.transport;
        msg.msg_namelen = conn->peer->srx.transport_len;
        msg.msg_control = NULL;
        msg.msg_controllen = 0;
        msg.msg_flags   = 0;

        whdr.epoch      = htonl(conn->proto.epoch);
        whdr.cid        = htonl(conn->proto.cid);
        whdr.callNumber = 0;
        whdr.seq        = 0;
        whdr.type       = RXRPC_PACKET_TYPE_CHALLENGE;
        whdr.flags      = conn->out_clientflag;
        whdr.userStatus = 0;
        whdr.securityIndex = conn->security_ix;
        whdr._rsvd      = 0;
        whdr.serviceId  = htons(conn->service_id);

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

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

        serial = rxrpc_get_next_serial(conn);
        whdr.serial = htonl(serial);

        trace_rxrpc_tx_challenge(conn, serial, 0, conn->rxkad.nonce);

        ret = kernel_sendmsg(conn->local->socket, &msg, iov, 2, len);
        if (ret < 0) {
                trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
                                    rxrpc_tx_point_rxkad_challenge);
                return -EAGAIN;
        }

        rxrpc_peer_mark_tx(conn->peer);
        trace_rxrpc_tx_packet(conn->debug_id, &whdr,
                              rxrpc_tx_point_rxkad_challenge);
        _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);
}

/*
 * encrypt the response packet
 */
static int rxkad_encrypt_response(struct rxrpc_connection *conn,
                                  struct sk_buff *response,
                                  const struct rxkad_key *s2)
{
        struct skcipher_request *req;
        struct rxrpc_crypt iv;
        struct scatterlist sg[1];
        size_t encsize = sizeof(((struct rxkad_response *)0)->encrypted);
        int ret;

        sg_init_table(sg, ARRAY_SIZE(sg));
        ret = skb_to_sgvec(response, sg,
                           sizeof(struct rxrpc_wire_header) +
                           offsetof(struct rxkad_response, encrypted), encsize);
        if (ret < 0)
                return ret;

        req = skcipher_request_alloc(&conn->rxkad.cipher->base, GFP_NOFS);
        if (!req)
                return -ENOMEM;

        /* continue encrypting from where we left off */
        memcpy(&iv, s2->session_key, sizeof(iv));

        skcipher_request_set_sync_tfm(req, conn->rxkad.cipher);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, sg, sg, encsize, iv.x);
        ret = crypto_skcipher_encrypt(req);
        skcipher_request_free(req);
        return ret;
}

/*
 * Validate a challenge packet.
 */
static bool rxkad_validate_challenge(struct rxrpc_connection *conn,
                                     struct sk_buff *skb)
{
        struct rxkad_challenge challenge;
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        u32 version, min_level;
        int ret;

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

        if (!conn->key) {
                rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
                                 rxkad_abort_chall_no_key);
                return false;
        }

        ret = key_validate(conn->key);
        if (ret < 0) {
                rxrpc_abort_conn(conn, skb, RXKADEXPIRED, ret,
                                 rxkad_abort_chall_key_expired);
                return false;
        }

        if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
                          &challenge, sizeof(challenge)) < 0) {
                rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
                                 rxkad_abort_chall_short);
                return false;
        }

        version = ntohl(challenge.version);
        sp->chall.rxkad_nonce = ntohl(challenge.nonce);
        min_level = ntohl(challenge.min_level);

        trace_rxrpc_rx_challenge(conn, sp->hdr.serial, version,
                                 sp->chall.rxkad_nonce, min_level);

        if (version != RXKAD_VERSION) {
                rxrpc_abort_conn(conn, skb, RXKADINCONSISTENCY, -EPROTO,
                                 rxkad_abort_chall_version);
                return false;
        }

        if (conn->security_level < min_level) {
                rxrpc_abort_conn(conn, skb, RXKADLEVELFAIL, -EACCES,
                                 rxkad_abort_chall_level);
                return false;
        }
        return true;
}

/*
 * Insert the header into the response.
 */
static noinline
int rxkad_insert_response_header(struct rxrpc_connection *conn,
                                 const struct rxrpc_key_token *token,
                                 struct sk_buff *challenge,
                                 struct sk_buff *response,
                                 size_t *offset)
{
        struct rxrpc_skb_priv *csp = rxrpc_skb(challenge);
        struct {
                struct rxrpc_wire_header whdr;
                struct rxkad_response   resp;
        } h;
        int ret;

        h.whdr.epoch                    = htonl(conn->proto.epoch);
        h.whdr.cid                      = htonl(conn->proto.cid);
        h.whdr.callNumber               = 0;
        h.whdr.serial                   = 0;
        h.whdr.seq                      = 0;
        h.whdr.type                     = RXRPC_PACKET_TYPE_RESPONSE;
        h.whdr.flags                    = conn->out_clientflag;
        h.whdr.userStatus               = 0;
        h.whdr.securityIndex            = conn->security_ix;
        h.whdr.cksum                    = 0;
        h.whdr.serviceId                = htons(conn->service_id);
        h.resp.version                  = htonl(RXKAD_VERSION);
        h.resp.__pad                    = 0;
        h.resp.encrypted.epoch          = htonl(conn->proto.epoch);
        h.resp.encrypted.cid            = htonl(conn->proto.cid);
        h.resp.encrypted.checksum       = 0;
        h.resp.encrypted.securityIndex  = htonl(conn->security_ix);
        h.resp.encrypted.call_id[0]     = htonl(conn->channels[0].call_counter);
        h.resp.encrypted.call_id[1]     = htonl(conn->channels[1].call_counter);
        h.resp.encrypted.call_id[2]     = htonl(conn->channels[2].call_counter);
        h.resp.encrypted.call_id[3]     = htonl(conn->channels[3].call_counter);
        h.resp.encrypted.inc_nonce      = htonl(csp->chall.rxkad_nonce + 1);
        h.resp.encrypted.level          = htonl(conn->security_level);
        h.resp.kvno                     = htonl(token->kad->kvno);
        h.resp.ticket_len               = htonl(token->kad->ticket_len);

        rxkad_calc_response_checksum(&h.resp);

        ret = skb_store_bits(response, *offset, &h, sizeof(h));
        *offset += sizeof(h);
        return ret;
}

/*
 * respond to a challenge packet
 */
static int rxkad_respond_to_challenge(struct rxrpc_connection *conn,
                                      struct sk_buff *challenge)
{
        const struct rxrpc_key_token *token;
        struct rxrpc_skb_priv *csp, *rsp;
        struct sk_buff *response;
        size_t len, offset = 0;
        int ret = -EPROTO;

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

        ret = key_validate(conn->key);
        if (ret < 0)
                return rxrpc_abort_conn(conn, challenge, RXKADEXPIRED, ret,
                                        rxkad_abort_chall_key_expired);

        token = conn->key->payload.data[0];

        /* build the response packet */
        len = sizeof(struct rxrpc_wire_header) +
                sizeof(struct rxkad_response) +
                token->kad->ticket_len;

        response = alloc_skb_with_frags(0, len, 0, &ret, GFP_NOFS);
        if (!response)
                goto error;
        rxrpc_new_skb(response, rxrpc_skb_new_response_rxkad);
        response->len = len;
        response->data_len = len;

        offset = 0;
        ret = rxkad_insert_response_header(conn, token, challenge, response,
                                           &offset);
        if (ret < 0)
                goto error;

        ret = rxkad_encrypt_response(conn, response, token->kad);
        if (ret < 0)
                goto error;

        ret = skb_store_bits(response, offset, token->kad->ticket,
                             token->kad->ticket_len);
        if (ret < 0)
                goto error;

        csp = rxrpc_skb(challenge);
        rsp = rxrpc_skb(response);
        rsp->resp.len = len;
        rsp->resp.challenge_serial = csp->hdr.serial;
        rxrpc_post_response(conn, response);
        response = NULL;
        ret = 0;

error:
        rxrpc_free_skb(response, rxrpc_skb_put_response);
        return ret;
}

/*
 * RxKAD does automatic response only as there's nothing to manage that isn't
 * already in the key.
 */
static int rxkad_sendmsg_respond_to_challenge(struct sk_buff *challenge,
                                              struct msghdr *msg)
{
        return -EINVAL;
}

/**
 * rxkad_kernel_respond_to_challenge - Respond to a challenge with appdata
 * @challenge: The challenge to respond to
 *
 * Allow a kernel application to respond to a CHALLENGE.
 *
 * Return: %0 if successful and a negative error code otherwise.
 */
int rxkad_kernel_respond_to_challenge(struct sk_buff *challenge)
{
        struct rxrpc_skb_priv *csp = rxrpc_skb(challenge);

        return rxkad_respond_to_challenge(csp->chall.conn, challenge);
}
EXPORT_SYMBOL(rxkad_kernel_respond_to_challenge);

/*
 * decrypt the kerberos IV ticket in the response
 */
static int rxkad_decrypt_ticket(struct rxrpc_connection *conn,
                                struct key *server_key,
                                struct sk_buff *skb,
                                void *ticket, size_t ticket_len,
                                struct rxrpc_crypt *_session_key,
                                time64_t *_expiry)
{
        struct skcipher_request *req;
        struct rxrpc_crypt iv, key;
        struct scatterlist sg[1];
        struct in_addr addr;
        unsigned int life;
        time64_t issue, now;
        bool little_endian;
        u8 *p, *q, *name, *end;

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

        *_expiry = 0;

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

        memcpy(&iv, &server_key->payload.data[2], sizeof(iv));

        req = skcipher_request_alloc(server_key->payload.data[0], GFP_NOFS);
        if (!req)
                return -ENOMEM;

        sg_init_one(&sg[0], ticket, ticket_len);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, sg, sg, ticket_len, iv.x);
        crypto_skcipher_decrypt(req);
        skcipher_request_free(req);

        p = ticket;
        end = p + ticket_len;

#define Z(field, fieldl)                                                \
        ({                                                              \
                u8 *__str = p;                                          \
                q = memchr(p, 0, end - p);                              \
                if (!q || q - p > field##_SZ)                           \
                        return rxrpc_abort_conn(                        \
                                conn, skb, RXKADBADTICKET, -EPROTO,     \
                                rxkad_abort_resp_tkt_##fieldl);         \
                for (; p < q; p++)                                      \
                        if (!isprint(*p))                               \
                                return rxrpc_abort_conn(                \
                                        conn, skb, RXKADBADTICKET, -EPROTO, \
                                        rxkad_abort_resp_tkt_##fieldl); \
                p++;                                                    \
                __str;                                                  \
        })

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

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

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

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

        if (end - p < 4 + 8 + 4 + 2)
                return rxrpc_abort_conn(conn, skb, RXKADBADTICKET, -EPROTO,
                                        rxkad_abort_resp_tkt_short);

        /* get the IPv4 address of the entity that requested the ticket */
        memcpy(&addr, p, sizeof(addr));
        p += 4;
        _debug("KIV ADDR : %pI4", &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 = rxrpc_u32_to_time64(le32_to_cpu(stamp));
        } else {
                __be32 stamp;
                memcpy(&stamp, p, 4);
                issue = rxrpc_u32_to_time64(be32_to_cpu(stamp));
        }
        p += 4;
        now = ktime_get_real_seconds();
        _debug("KIV ISSUE: %llx [%llx]", issue, now);

        /* check the ticket is in date */
        if (issue > now)
                return rxrpc_abort_conn(conn, skb, RXKADNOAUTH, -EKEYREJECTED,
                                        rxkad_abort_resp_tkt_future);
        if (issue < now - life)
                return rxrpc_abort_conn(conn, skb, RXKADEXPIRED, -EKEYEXPIRED,
                                        rxkad_abort_resp_tkt_expired);

        *_expiry = issue + life;

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

        /* get the service instance name */
        name = Z(INST, sinst);
        _debug("KIV SINST: %s", name);
        return 0;
}

/*
 * decrypt the response packet
 */
static void rxkad_decrypt_response(struct rxrpc_connection *conn,
                                   struct rxkad_response *resp,
                                   const struct rxrpc_crypt *session_key)
{
        struct skcipher_request *req = rxkad_ci_req;
        struct scatterlist sg[1];
        struct rxrpc_crypt iv;

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

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

        memcpy(&iv, session_key, sizeof(iv));

        sg_init_table(sg, 1);
        sg_set_buf(sg, &resp->encrypted, sizeof(resp->encrypted));
        skcipher_request_set_sync_tfm(req, rxkad_ci);
        skcipher_request_set_callback(req, 0, NULL, NULL);
        skcipher_request_set_crypt(req, sg, sg, sizeof(resp->encrypted), iv.x);
        crypto_skcipher_decrypt(req);
        skcipher_request_zero(req);

        mutex_unlock(&rxkad_ci_mutex);

        _leave("");
}

/*
 * verify a response
 */
static int rxkad_verify_response(struct rxrpc_connection *conn,
                                 struct sk_buff *skb)
{
        struct rxkad_response *response;
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        struct rxrpc_crypt session_key;
        struct key *server_key;
        time64_t expiry;
        void *ticket;
        u32 version, kvno, ticket_len, level;
        __be32 csum;
        int ret, i;

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

        server_key = rxrpc_look_up_server_security(conn, skb, 0, 0);
        if (IS_ERR(server_key)) {
                ret = PTR_ERR(server_key);
                switch (ret) {
                case -ENOKEY:
                        return rxrpc_abort_conn(conn, skb, RXKADUNKNOWNKEY, ret,
                                                rxkad_abort_resp_nokey);
                case -EKEYEXPIRED:
                        return rxrpc_abort_conn(conn, skb, RXKADEXPIRED, ret,
                                                rxkad_abort_resp_key_expired);
                default:
                        return rxrpc_abort_conn(conn, skb, RXKADNOAUTH, ret,
                                                rxkad_abort_resp_key_rejected);
                }
        }

        ret = -ENOMEM;
        response = kzalloc_obj(struct rxkad_response, GFP_NOFS);
        if (!response)
                goto temporary_error;

        if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
                          response, sizeof(*response)) < 0) {
                rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
                                 rxkad_abort_resp_short);
                goto protocol_error;
        }

        version = ntohl(response->version);
        ticket_len = ntohl(response->ticket_len);
        kvno = ntohl(response->kvno);

        trace_rxrpc_rx_response(conn, sp->hdr.serial, version, kvno, ticket_len);

        if (version != RXKAD_VERSION) {
                rxrpc_abort_conn(conn, skb, RXKADINCONSISTENCY, -EPROTO,
                                 rxkad_abort_resp_version);
                goto protocol_error;
        }

        if (ticket_len < 4 || ticket_len > MAXKRB5TICKETLEN) {
                rxrpc_abort_conn(conn, skb, RXKADTICKETLEN, -EPROTO,
                                 rxkad_abort_resp_tkt_len);
                goto protocol_error;
        }

        if (kvno >= RXKAD_TKT_TYPE_KERBEROS_V5) {
                rxrpc_abort_conn(conn, skb, RXKADUNKNOWNKEY, -EPROTO,
                                 rxkad_abort_resp_unknown_tkt);
                goto protocol_error;
        }

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

        if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header) + sizeof(*response),
                          ticket, ticket_len) < 0) {
                rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
                                 rxkad_abort_resp_short_tkt);
                goto protocol_error;
        }

        ret = rxkad_decrypt_ticket(conn, server_key, skb, ticket, ticket_len,
                                   &session_key, &expiry);
        if (ret < 0)
                goto temporary_error_free_ticket;

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

        if (ntohl(response->encrypted.epoch) != conn->proto.epoch ||
            ntohl(response->encrypted.cid) != conn->proto.cid ||
            ntohl(response->encrypted.securityIndex) != conn->security_ix) {
                rxrpc_abort_conn(conn, skb, RXKADSEALEDINCON, -EPROTO,
                                 rxkad_abort_resp_bad_param);
                goto protocol_error_free;
        }

        csum = response->encrypted.checksum;
        response->encrypted.checksum = 0;
        rxkad_calc_response_checksum(response);
        if (response->encrypted.checksum != csum) {
                rxrpc_abort_conn(conn, skb, RXKADSEALEDINCON, -EPROTO,
                                 rxkad_abort_resp_bad_checksum);
                goto protocol_error_free;
        }

        for (i = 0; i < RXRPC_MAXCALLS; i++) {
                u32 call_id = ntohl(response->encrypted.call_id[i]);
                u32 counter = READ_ONCE(conn->channels[i].call_counter);

                if (call_id > INT_MAX) {
                        rxrpc_abort_conn(conn, skb, RXKADSEALEDINCON, -EPROTO,
                                         rxkad_abort_resp_bad_callid);
                        goto protocol_error_free;
                }

                if (call_id < counter) {
                        rxrpc_abort_conn(conn, skb, RXKADSEALEDINCON, -EPROTO,
                                         rxkad_abort_resp_call_ctr);
                        goto protocol_error_free;
                }

                if (call_id > counter) {
                        if (conn->channels[i].call) {
                                rxrpc_abort_conn(conn, skb, RXKADSEALEDINCON, -EPROTO,
                                                 rxkad_abort_resp_call_state);
                                goto protocol_error_free;
                        }
                        conn->channels[i].call_counter = call_id;
                }
        }

        if (ntohl(response->encrypted.inc_nonce) != conn->rxkad.nonce + 1) {
                rxrpc_abort_conn(conn, skb, RXKADOUTOFSEQUENCE, -EPROTO,
                                 rxkad_abort_resp_ooseq);
                goto protocol_error_free;
        }

        level = ntohl(response->encrypted.level);
        if (level > RXRPC_SECURITY_ENCRYPT) {
                rxrpc_abort_conn(conn, skb, RXKADLEVELFAIL, -EPROTO,
                                 rxkad_abort_resp_level);
                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)
                goto temporary_error_free_ticket;

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

protocol_error_free:
        kfree(ticket);
protocol_error:
        kfree(response);
        key_put(server_key);
        return -EPROTO;

temporary_error_free_ticket:
        kfree(ticket);
temporary_error_free_resp:
        kfree(response);
temporary_error:
        /* Ignore the response packet if we got a temporary error such as
         * ENOMEM.  We just want to send the challenge again.  Note that we
         * also come out this way if the ticket decryption fails.
         */
        key_put(server_key);
        return ret;
}

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

        if (conn->rxkad.cipher)
                crypto_free_sync_skcipher(conn->rxkad.cipher);
}

/*
 * Initialise the rxkad security service.
 */
static int rxkad_init(void)
{
        struct crypto_sync_skcipher *tfm;
        struct skcipher_request *req;

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

        req = skcipher_request_alloc(&tfm->base, GFP_KERNEL);
        if (!req)
                goto nomem_tfm;

        rxkad_ci_req = req;
        rxkad_ci = tfm;
        return 0;

nomem_tfm:
        crypto_free_sync_skcipher(tfm);
        return -ENOMEM;
}

/*
 * Clean up the rxkad security service.
 */
static void rxkad_exit(void)
{
        crypto_free_sync_skcipher(rxkad_ci);
        skcipher_request_free(rxkad_ci_req);
}

/*
 * RxRPC Kerberos-based security
 */
const struct rxrpc_security rxkad = {
        .name                           = "rxkad",
        .security_index                 = RXRPC_SECURITY_RXKAD,
        .no_key_abort                   = RXKADUNKNOWNKEY,
        .init                           = rxkad_init,
        .exit                           = rxkad_exit,
        .preparse_server_key            = rxkad_preparse_server_key,
        .free_preparse_server_key       = rxkad_free_preparse_server_key,
        .destroy_server_key             = rxkad_destroy_server_key,
        .init_connection_security       = rxkad_init_connection_security,
        .alloc_txbuf                    = rxkad_alloc_txbuf,
        .secure_packet                  = rxkad_secure_packet,
        .verify_packet                  = rxkad_verify_packet,
        .free_call_crypto               = rxkad_free_call_crypto,
        .issue_challenge                = rxkad_issue_challenge,
        .validate_challenge             = rxkad_validate_challenge,
        .sendmsg_respond_to_challenge   = rxkad_sendmsg_respond_to_challenge,
        .respond_to_challenge           = rxkad_respond_to_challenge,
        .verify_response                = rxkad_verify_response,
        .clear                          = rxkad_clear,
};