[PATCH net-next v2 05/13] rxrpc: Add YFS RxGK (GSSAPI) security class

[PATCH net-next v2 05/13] rxrpc: Add YFS RxGK (GSSAPI) security class

[David Howells]

Add support for the YFS-variant RxGK security class to support
GSSAPI-derived authentication.  This also allows the use of better crypto
over the rxkad security class.

The key payload is XDR encoded of the form:

    typedef int64_t opr_time;

    const AFSTOKEN_RK_TIX_MAX = 12000; 	/* Matches entry in rxkad.h */

    struct token_rxkad {
	afs_int32 viceid;
	afs_int32 kvno;
	afs_int64 key;
	afs_int32 begintime;
	afs_int32 endtime;
	afs_int32 primary_flag;
	opaque ticket<AFSTOKEN_RK_TIX_MAX>;
    };

    struct token_rxgk {
	opr_time begintime;
	opr_time endtime;
	afs_int64 level;
	afs_int64 lifetime;
	afs_int64 bytelife;
	afs_int64 enctype;
	opaque key<>;
	opaque ticket<>;
    };

    const AFSTOKEN_UNION_NOAUTH = 0;
    const AFSTOKEN_UNION_KAD = 2;
    const AFSTOKEN_UNION_YFSGK = 6;

    union ktc_tokenUnion switch (afs_int32 type) {
	case AFSTOKEN_UNION_KAD:
	    token_rxkad kad;
	case AFSTOKEN_UNION_YFSGK:
	    token_rxgk  gk;
    };

    const AFSTOKEN_LENGTH_MAX = 16384;
    typedef opaque token_opaque<AFSTOKEN_LENGTH_MAX>;

    const AFSTOKEN_MAX = 8;
    const AFSTOKEN_CELL_MAX = 64;

    struct ktc_setTokenData {
	afs_int32 flags;
	string cell<AFSTOKEN_CELL_MAX>;
	token_opaque tokens<AFSTOKEN_MAX>;
    };

The parser for the basic token struct is already present, as is the rxkad
token type.  This adds a parser for the rxgk token type.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
 include/keys/rxrpc-type.h |  17 ++++
 net/rxrpc/key.c           | 185 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 202 insertions(+)

diff --git a/include/keys/rxrpc-type.h b/include/keys/rxrpc-type.h
index 333c0f49a9cd..0ddbe197a261 100644
--- a/include/keys/rxrpc-type.h
+++ b/include/keys/rxrpc-type.h
@@ -9,6 +9,7 @@
 #define _KEYS_RXRPC_TYPE_H
 
 #include <linux/key.h>
+#include <crypto/krb5.h>
 
 /*
  * key type for AF_RXRPC keys
@@ -31,6 +32,21 @@ struct rxkad_key {
 	u8	ticket[];		/* the encrypted ticket */
 };
 
+/*
+ * RxRPC key for YFS-RxGK (type-6 security)
+ */
+struct rxgk_key {
+	s64		begintime;	/* Time at which the ticket starts */
+	s64		endtime;	/* Time at which the ticket ends */
+	u64		lifetime;	/* Maximum lifespan of a connection (seconds) */
+	u64		bytelife;	/* Maximum number of bytes on a connection */
+	unsigned int	enctype;	/* Encoding type */
+	s8		level;		/* Negotiated security RXRPC_SECURITY_PLAIN/AUTH/ENCRYPT */
+	struct krb5_buffer key;		/* Master key, K0 */
+	struct krb5_buffer ticket;	/* Ticket to be passed to server */
+	u8		_key[];		/* Key storage */
+};
+
 /*
  * list of tokens attached to an rxrpc key
  */
@@ -40,6 +56,7 @@ struct rxrpc_key_token {
 	struct rxrpc_key_token *next;	/* the next token in the list */
 	union {
 		struct rxkad_key *kad;
+		struct rxgk_key *rxgk;
 	};
 };
 
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 8c99cf19b19d..9fdc1f031c9d 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -129,6 +129,160 @@ static int rxrpc_preparse_xdr_rxkad(struct key_preparsed_payload *prep,
 	return 0;
 }
 
+static u64 xdr_dec64(const __be32 *xdr)
+{
+	return (u64)ntohl(xdr[0]) << 32 | (u64)ntohl(xdr[1]);
+}
+
+static time64_t rxrpc_s64_to_time64(s64 time_in_100ns)
+{
+	bool neg = false;
+	u64 tmp = time_in_100ns;
+
+	if (time_in_100ns < 0) {
+		tmp = -time_in_100ns;
+		neg = true;
+	}
+	do_div(tmp, 10000000);
+	return neg ? -tmp : tmp;
+}
+
+/*
+ * Parse a YFS-RxGK type XDR format token
+ * - the caller guarantees we have at least 4 words
+ *
+ * struct token_rxgk {
+ *	opr_time begintime;
+ *	opr_time endtime;
+ *	afs_int64 level;
+ *	afs_int64 lifetime;
+ *	afs_int64 bytelife;
+ *	afs_int64 enctype;
+ *	opaque key<>;
+ *	opaque ticket<>;
+ * };
+ */
+static int rxrpc_preparse_xdr_yfs_rxgk(struct key_preparsed_payload *prep,
+				       size_t datalen,
+				       const __be32 *xdr, unsigned int toklen)
+{
+	struct rxrpc_key_token *token, **pptoken;
+	time64_t expiry;
+	size_t plen;
+	const __be32 *ticket, *key;
+	s64 tmp;
+	u32 tktlen, keylen;
+
+	_enter(",{%x,%x,%x,%x},%x",
+	       ntohl(xdr[0]), ntohl(xdr[1]), ntohl(xdr[2]), ntohl(xdr[3]),
+	       toklen);
+
+	if (6 * 2 + 2 > toklen / 4)
+		goto reject;
+
+	key = xdr + (6 * 2 + 1);
+	keylen = ntohl(key[-1]);
+	_debug("keylen: %x", keylen);
+	keylen = round_up(keylen, 4);
+	if ((6 * 2 + 2) * 4 + keylen > toklen)
+		goto reject;
+
+	ticket = xdr + (6 * 2 + 1 + (keylen / 4) + 1);
+	tktlen = ntohl(ticket[-1]);
+	_debug("tktlen: %x", tktlen);
+	tktlen = round_up(tktlen, 4);
+	if ((6 * 2 + 2) * 4 + keylen + tktlen != toklen) {
+		kleave(" = -EKEYREJECTED [%x!=%x, %x,%x]",
+		       (6 * 2 + 2) * 4 + keylen + tktlen, toklen,
+		       keylen, tktlen);
+		goto reject;
+	}
+
+	plen = sizeof(*token) + sizeof(*token->rxgk) + tktlen + keylen;
+	prep->quotalen = datalen + plen;
+
+	plen -= sizeof(*token);
+	token = kzalloc(sizeof(*token), GFP_KERNEL);
+	if (!token)
+		goto nomem;
+
+	token->rxgk = kzalloc(sizeof(*token->rxgk) + keylen, GFP_KERNEL);
+	if (!token->rxgk)
+		goto nomem_token;
+
+	token->security_index	= RXRPC_SECURITY_YFS_RXGK;
+	token->rxgk->begintime	= xdr_dec64(xdr + 0 * 2);
+	token->rxgk->endtime	= xdr_dec64(xdr + 1 * 2);
+	token->rxgk->level	= tmp = xdr_dec64(xdr + 2 * 2);
+	if (tmp < -1LL || tmp > RXRPC_SECURITY_ENCRYPT)
+		goto reject_token;
+	token->rxgk->lifetime	= xdr_dec64(xdr + 3 * 2);
+	token->rxgk->bytelife	= xdr_dec64(xdr + 4 * 2);
+	token->rxgk->enctype	= tmp = xdr_dec64(xdr + 5 * 2);
+	if (tmp < 0 || tmp > UINT_MAX)
+		goto reject_token;
+	token->rxgk->key.len	= ntohl(key[-1]);
+	token->rxgk->key.data	= token->rxgk->_key;
+	token->rxgk->ticket.len = ntohl(ticket[-1]);
+
+	if (token->rxgk->endtime != 0) {
+		expiry = rxrpc_s64_to_time64(token->rxgk->endtime);
+		if (expiry < 0)
+			goto expired;
+		if (expiry < prep->expiry)
+			prep->expiry = expiry;
+	}
+
+	memcpy(token->rxgk->key.data, key, token->rxgk->key.len);
+
+	/* Pad the ticket so that we can use it directly in XDR */
+	token->rxgk->ticket.data = kzalloc(round_up(token->rxgk->ticket.len, 4),
+					   GFP_KERNEL);
+	if (!token->rxgk->ticket.data)
+		goto nomem_yrxgk;
+	memcpy(token->rxgk->ticket.data, ticket, token->rxgk->ticket.len);
+
+	_debug("SCIX: %u",	token->security_index);
+	_debug("EXPY: %llx",	token->rxgk->endtime);
+	_debug("LIFE: %llx",	token->rxgk->lifetime);
+	_debug("BYTE: %llx",	token->rxgk->bytelife);
+	_debug("ENC : %u",	token->rxgk->enctype);
+	_debug("LEVL: %u",	token->rxgk->level);
+	_debug("KLEN: %u",	token->rxgk->key.len);
+	_debug("TLEN: %u",	token->rxgk->ticket.len);
+	_debug("KEY0: %*phN",	token->rxgk->key.len, token->rxgk->key.data);
+	_debug("TICK: %*phN",
+	       min_t(u32, token->rxgk->ticket.len, 32), token->rxgk->ticket.data);
+
+	/* count the number of tokens attached */
+	prep->payload.data[1] = (void *)((unsigned long)prep->payload.data[1] + 1);
+
+	/* attach the data */
+	for (pptoken = (struct rxrpc_key_token **)&prep->payload.data[0];
+	     *pptoken;
+	     pptoken = &(*pptoken)->next)
+		continue;
+	*pptoken = token;
+
+	_leave(" = 0");
+	return 0;
+
+nomem_yrxgk:
+	kfree(token->rxgk);
+nomem_token:
+	kfree(token);
+nomem:
+	return -ENOMEM;
+reject_token:
+	kfree(token);
+reject:
+	return -EKEYREJECTED;
+expired:
+	kfree(token->rxgk);
+	kfree(token);
+	return -EKEYEXPIRED;
+}
+
 /*
  * attempt to parse the data as the XDR format
  * - the caller guarantees we have more than 7 words
@@ -228,6 +382,9 @@ static int rxrpc_preparse_xdr(struct key_preparsed_payload *prep)
 		case RXRPC_SECURITY_RXKAD:
 			ret2 = rxrpc_preparse_xdr_rxkad(prep, datalen, token, toklen);
 			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			ret2 = rxrpc_preparse_xdr_yfs_rxgk(prep, datalen, token, toklen);
+			break;
 		default:
 			ret2 = -EPROTONOSUPPORT;
 			break;
@@ -390,6 +547,10 @@ static void rxrpc_free_token_list(struct rxrpc_key_token *token)
 		case RXRPC_SECURITY_RXKAD:
 			kfree(token->kad);
 			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			kfree(token->rxgk->ticket.data);
+			kfree(token->rxgk);
+			break;
 		default:
 			pr_err("Unknown token type %x on rxrpc key\n",
 			       token->security_index);
@@ -433,6 +594,9 @@ static void rxrpc_describe(const struct key *key, struct seq_file *m)
 		case RXRPC_SECURITY_RXKAD:
 			seq_puts(m, "ka");
 			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			seq_puts(m, "ygk");
+			break;
 		default: /* we have a ticket we can't encode */
 			seq_printf(m, "%u", token->security_index);
 			break;
@@ -597,6 +761,13 @@ static long rxrpc_read(const struct key *key,
 				toksize += RND(token->kad->ticket_len);
 			break;
 
+		case RXRPC_SECURITY_YFS_RXGK:
+			toksize += 6 * 8 + 2 * 4;
+			if (!token->no_leak_key)
+				toksize += RND(token->rxgk->key.len);
+			toksize += RND(token->rxgk->ticket.len);
+			break;
+
 		default: /* we have a ticket we can't encode */
 			pr_err("Unsupported key token type (%u)\n",
 			       token->security_index);
@@ -676,6 +847,20 @@ static long rxrpc_read(const struct key *key,
 				ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
 			break;
 
+		case RXRPC_SECURITY_YFS_RXGK:
+			ENCODE64(token->rxgk->begintime);
+			ENCODE64(token->rxgk->endtime);
+			ENCODE64(token->rxgk->level);
+			ENCODE64(token->rxgk->lifetime);
+			ENCODE64(token->rxgk->bytelife);
+			ENCODE64(token->rxgk->enctype);
+			if (token->no_leak_key)
+				ENCODE(0);
+			else
+				ENCODE_DATA(token->rxgk->key.len, token->rxgk->key.data);
+			ENCODE_DATA(token->rxgk->ticket.len, token->rxgk->ticket.data);
+			break;
+
 		default:
 			pr_err("Unsupported key token type (%u)\n",
 			       token->security_index);

[PATCH net-next v2 06/13] rxrpc: rxgk: Provide infrastructure and key derivation

[David Howells]

Provide some infrastructure for implementing the RxGK transport security
class:

 (1) A definition of an encoding type, including:

	- Relevant crypto-layer names
	- Lengths of the crypto keys and checksums involved
	- Crypto functions specific to the encoding type
	- Crypto scheme used for that type

 (2) A definition of a crypto scheme, including:

	- Underlying crypto handlers
	- The pseudo-random function, PRF, used in base key derivation
	- Functions for deriving usage keys Kc, Ke and Ki
	- Functions for en/decrypting parts of an sk_buff

 (3) A key context, with the usage keys required for a derivative of a
     transport key for a specific key number.  This includes keys for
     securing packets for transmission, extracting received packets and
     dealing with response packets.

 (3) A function to look up an encoding type by number.

 (4) A function to set up a key context and derive the keys.

 (5) A function to set up the keys required to extract the ticket obtained
     from the GSS negotiation in the server.

 (6) Miscellaneous functions for context handling.

The keys and key derivation functions are described in:

	tools.ietf.org/html/draft-wilkinson-afs3-rxgk-11

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
 net/rxrpc/Kconfig       |  23 ++++
 net/rxrpc/Makefile      |   3 +-
 net/rxrpc/ar-internal.h |   3 +
 net/rxrpc/rxgk_common.h |  48 +++++++
 net/rxrpc/rxgk_kdf.c    | 287 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 363 insertions(+), 1 deletion(-)
 create mode 100644 net/rxrpc/rxgk_common.h
 create mode 100644 net/rxrpc/rxgk_kdf.c

diff --git a/net/rxrpc/Kconfig b/net/rxrpc/Kconfig
index a20986806fea..f60b81c66078 100644
--- a/net/rxrpc/Kconfig
+++ b/net/rxrpc/Kconfig
@@ -67,6 +67,29 @@ config RXKAD
 
 	  See Documentation/networking/rxrpc.rst.
 
+config RXGK
+	bool "RxRPC GSSAPI security"
+	select CRYPTO_KRB5
+	select CRYPTO_MANAGER
+	select CRYPTO_KRB5ENC
+	select CRYPTO_AUTHENC
+	select CRYPTO_SKCIPHER
+	select CRYPTO_HASH_INFO
+	select CRYPTO_HMAC
+	select CRYPTO_CMAC
+	select CRYPTO_SHA1
+	select CRYPTO_SHA256
+	select CRYPTO_SHA512
+	select CRYPTO_CBC
+	select CRYPTO_CTS
+	select CRYPTO_AES
+	select CRYPTO_CAMELLIA
+	help
+	  Provide the GSSAPI-based RxGK security class for AFS.  Keys are added
+	  with add_key().
+
+	  See Documentation/networking/rxrpc.rst.
+
 config RXPERF
 	tristate "RxRPC test service"
 	help
diff --git a/net/rxrpc/Makefile b/net/rxrpc/Makefile
index 0981941dea73..3eda77a0266b 100644
--- a/net/rxrpc/Makefile
+++ b/net/rxrpc/Makefile
@@ -40,6 +40,7 @@ rxrpc-y := \
 rxrpc-$(CONFIG_PROC_FS) += proc.o
 rxrpc-$(CONFIG_RXKAD) += rxkad.o
 rxrpc-$(CONFIG_SYSCTL) += sysctl.o
-
+rxrpc-$(CONFIG_RXGK) += \
+	rxgk_kdf.o
 
 obj-$(CONFIG_RXPERF) += rxperf.o
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 6b27295495f5..81bacac94430 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -558,6 +558,9 @@ struct rxrpc_connection {
 			struct rxrpc_crypt csum_iv;	/* packet checksum base */
 			u32	nonce;		/* response re-use preventer */
 		} rxkad;
+		struct {
+			u64	start_time;	/* The start time for TK derivation */
+		} rxgk;
 	};
 	struct sk_buff		*tx_response;	/* Response packet to be transmitted */
 	unsigned long		flags;
diff --git a/net/rxrpc/rxgk_common.h b/net/rxrpc/rxgk_common.h
new file mode 100644
index 000000000000..da1464e65766
--- /dev/null
+++ b/net/rxrpc/rxgk_common.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Common bits for GSSAPI-based RxRPC security.
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <crypto/krb5.h>
+#include <crypto/skcipher.h>
+#include <crypto/hash.h>
+
+/*
+ * Per-key number context.  This is replaced when the connection is rekeyed.
+ */
+struct rxgk_context {
+	refcount_t		usage;
+	unsigned int		key_number;	/* Rekeying number (goes in the rx header) */
+	unsigned long		flags;
+#define RXGK_TK_NEEDS_REKEY	0		/* Set if this needs rekeying */
+	unsigned long		expiry;		/* Expiration time of this key */
+	long long		bytes_remaining; /* Remaining Tx lifetime of this key */
+	const struct krb5_enctype *krb5;	/* RxGK encryption type */
+	const struct rxgk_key	*key;
+
+	/* We need up to 7 keys derived from the transport key, but we don't
+	 * actually need the transport key.  Each key is derived by
+	 * DK(TK,constant).
+	 */
+	struct crypto_aead	*tx_enc;	/* Transmission key */
+	struct crypto_aead	*rx_enc;	/* Reception key */
+	struct crypto_shash	*tx_Kc;		/* Transmission checksum key */
+	struct crypto_shash	*rx_Kc;		/* Reception checksum key */
+	struct crypto_aead	*resp_enc;	/* Response packet enc key */
+};
+
+/*
+ * rxgk_kdf.c
+ */
+void rxgk_put(struct rxgk_context *gk);
+struct rxgk_context *rxgk_generate_transport_key(struct rxrpc_connection *conn,
+						 const struct rxgk_key *key,
+						 unsigned int key_number,
+						 gfp_t gfp);
+int rxgk_set_up_token_cipher(const struct krb5_buffer *server_key,
+			     struct crypto_aead **token_key,
+			     unsigned int enctype,
+			     const struct krb5_enctype **_krb5,
+			     gfp_t gfp);
diff --git a/net/rxrpc/rxgk_kdf.c b/net/rxrpc/rxgk_kdf.c
new file mode 100644
index 000000000000..b18a9f16247f
--- /dev/null
+++ b/net/rxrpc/rxgk_kdf.c
@@ -0,0 +1,287 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* RxGK transport key derivation.
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/key-type.h>
+#include <linux/slab.h>
+#include <keys/rxrpc-type.h>
+#include "ar-internal.h"
+#include "rxgk_common.h"
+
+#define round16(x) (((x) + 15) & ~15)
+
+/*
+ * Constants used to derive the keys and hmacs actually used for doing stuff.
+ */
+#define RXGK_CLIENT_ENC_PACKET		1026U // 0x402
+#define RXGK_CLIENT_MIC_PACKET          1027U // 0x403
+#define RXGK_SERVER_ENC_PACKET          1028U // 0x404
+#define RXGK_SERVER_MIC_PACKET          1029U // 0x405
+#define RXGK_CLIENT_ENC_RESPONSE        1030U // 0x406
+#define RXGK_SERVER_ENC_TOKEN           1036U // 0x40c
+
+static void rxgk_free(struct rxgk_context *gk)
+{
+	if (gk->tx_Kc)
+		crypto_free_shash(gk->tx_Kc);
+	if (gk->rx_Kc)
+		crypto_free_shash(gk->rx_Kc);
+	if (gk->tx_enc)
+		crypto_free_aead(gk->tx_enc);
+	if (gk->rx_enc)
+		crypto_free_aead(gk->rx_enc);
+	if (gk->resp_enc)
+		crypto_free_aead(gk->resp_enc);
+	kfree(gk);
+}
+
+void rxgk_put(struct rxgk_context *gk)
+{
+	if (gk && refcount_dec_and_test(&gk->usage))
+		rxgk_free(gk);
+}
+
+/*
+ * Transport key derivation function.
+ *
+ *      TK = random-to-key(PRF+(K0, L,
+ *                         epoch || cid || start_time || key_number))
+ *      [tools.ietf.org/html/draft-wilkinson-afs3-rxgk-11 sec 8.3]
+ */
+static int rxgk_derive_transport_key(struct rxrpc_connection *conn,
+				     struct rxgk_context *gk,
+				     const struct rxgk_key *rxgk,
+				     struct krb5_buffer *TK,
+				     gfp_t gfp)
+{
+	const struct krb5_enctype *krb5 = gk->krb5;
+	struct krb5_buffer conn_info;
+	unsigned int L = krb5->key_bytes;
+	__be32 *info;
+	u8 *buffer;
+	int ret;
+
+	_enter("");
+
+	conn_info.len = sizeof(__be32) * 5;
+
+	buffer = kzalloc(round16(conn_info.len), gfp);
+	if (!buffer)
+		return -ENOMEM;
+
+	conn_info.data = buffer;
+
+	info = (__be32 *)conn_info.data;
+	info[0] = htonl(conn->proto.epoch);
+	info[1] = htonl(conn->proto.cid);
+	info[2] = htonl(conn->rxgk.start_time >> 32);
+	info[3] = htonl(conn->rxgk.start_time >>  0);
+	info[4] = htonl(gk->key_number);
+
+	ret = crypto_krb5_calc_PRFplus(krb5, &rxgk->key, L, &conn_info, TK, gfp);
+	kfree_sensitive(buffer);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Set up the ciphers for the usage keys.
+ */
+static int rxgk_set_up_ciphers(struct rxrpc_connection *conn,
+			       struct rxgk_context *gk,
+			       const struct rxgk_key *rxgk,
+			       gfp_t gfp)
+{
+	const struct krb5_enctype *krb5 = gk->krb5;
+	struct crypto_shash *shash;
+	struct crypto_aead *aead;
+	struct krb5_buffer TK;
+	bool service = rxrpc_conn_is_service(conn);
+	int ret;
+	u8 *buffer;
+
+	buffer = kzalloc(krb5->key_bytes, gfp);
+	if (!buffer)
+		return -ENOMEM;
+
+	TK.len = krb5->key_bytes;
+	TK.data = buffer;
+
+	ret = rxgk_derive_transport_key(conn, gk, rxgk, &TK, gfp);
+	if (ret < 0)
+		goto out;
+
+	aead = crypto_krb5_prepare_encryption(krb5, &TK, RXGK_CLIENT_ENC_RESPONSE, gfp);
+	if (IS_ERR(aead))
+		goto aead_error;
+	gk->resp_enc = aead;
+
+	if (crypto_aead_blocksize(gk->resp_enc) != krb5->block_len ||
+	    crypto_aead_authsize(gk->resp_enc) != krb5->cksum_len) {
+		pr_notice("algo inconsistent with krb5 table %u!=%u or %u!=%u\n",
+			  crypto_aead_blocksize(gk->resp_enc), krb5->block_len,
+			  crypto_aead_authsize(gk->resp_enc), krb5->cksum_len);
+		return -EINVAL;
+	}
+
+	if (service) {
+		switch (conn->security_level) {
+		case RXRPC_SECURITY_AUTH:
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_SERVER_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->tx_Kc = shash;
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_CLIENT_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->rx_Kc = shash;
+			break;
+		case RXRPC_SECURITY_ENCRYPT:
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_SERVER_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->tx_enc = aead;
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_CLIENT_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->rx_enc = aead;
+			break;
+		}
+	} else {
+		switch (conn->security_level) {
+		case RXRPC_SECURITY_AUTH:
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_CLIENT_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->tx_Kc = shash;
+			shash = crypto_krb5_prepare_checksum(
+				krb5, &TK, RXGK_SERVER_MIC_PACKET, gfp);
+			if (IS_ERR(shash))
+				goto hash_error;
+			gk->rx_Kc = shash;
+			break;
+		case RXRPC_SECURITY_ENCRYPT:
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_CLIENT_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->tx_enc = aead;
+			aead = crypto_krb5_prepare_encryption(
+				krb5, &TK, RXGK_SERVER_ENC_PACKET, gfp);
+			if (IS_ERR(aead))
+				goto aead_error;
+			gk->rx_enc = aead;
+			break;
+		}
+	}
+
+	ret = 0;
+out:
+	kfree_sensitive(buffer);
+	return ret;
+aead_error:
+	ret = PTR_ERR(aead);
+	goto out;
+hash_error:
+	ret = PTR_ERR(shash);
+	goto out;
+}
+
+/*
+ * Derive a transport key for a connection and then derive a bunch of usage
+ * keys from it and set up ciphers using them.
+ */
+struct rxgk_context *rxgk_generate_transport_key(struct rxrpc_connection *conn,
+						 const struct rxgk_key *key,
+						 unsigned int key_number,
+						 gfp_t gfp)
+{
+	struct rxgk_context *gk;
+	unsigned long lifetime;
+	int ret = -ENOPKG;
+
+	_enter("");
+
+	gk = kzalloc(sizeof(*gk), GFP_KERNEL);
+	if (!gk)
+		return ERR_PTR(-ENOMEM);
+	refcount_set(&gk->usage, 1);
+	gk->key		= key;
+	gk->key_number	= key_number;
+
+	gk->krb5 = crypto_krb5_find_enctype(key->enctype);
+	if (!gk->krb5)
+		goto err_tk;
+
+	ret = rxgk_set_up_ciphers(conn, gk, key, gfp);
+	if (ret)
+		goto err_tk;
+
+	/* Set the remaining number of bytes encrypted with this key that may
+	 * be transmitted before rekeying.  Note that the spec has been
+	 * interpreted differently on this point...
+	 */
+	switch (key->bytelife) {
+	case 0:
+	case 63:
+		gk->bytes_remaining = LLONG_MAX;
+		break;
+	case 1 ... 62:
+		gk->bytes_remaining = 1LL << key->bytelife;
+		break;
+	default:
+		gk->bytes_remaining = key->bytelife;
+		break;
+	}
+
+	/* Set the time after which rekeying must occur */
+	if (key->lifetime) {
+		lifetime = min_t(u64, key->lifetime, INT_MAX / HZ);
+		lifetime *= HZ;
+	} else {
+		lifetime = MAX_JIFFY_OFFSET;
+	}
+	gk->expiry = jiffies + lifetime;
+	return gk;
+
+err_tk:
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ERR_PTR(ret);
+}
+
+/*
+ * Use the server secret key to set up the ciphers that will be used to extract
+ * the token from a response packet.
+ */
+int rxgk_set_up_token_cipher(const struct krb5_buffer *server_key,
+			     struct crypto_aead **token_aead,
+			     unsigned int enctype,
+			     const struct krb5_enctype **_krb5,
+			     gfp_t gfp)
+{
+	const struct krb5_enctype *krb5;
+	struct crypto_aead *aead;
+
+	krb5 = crypto_krb5_find_enctype(enctype);
+	if (!krb5)
+		return -ENOPKG;
+
+	aead = crypto_krb5_prepare_encryption(krb5, server_key, RXGK_SERVER_ENC_TOKEN, gfp);
+	if (IS_ERR(aead))
+		return PTR_ERR(aead);
+
+	*_krb5 = krb5;
+	*token_aead = aead;
+	return 0;
+}

Re: [PATCH net-next v2 06/13] rxrpc: rxgk: Provide infrastructure and key derivation

[Jakub Kicinski]

On Mon,  7 Apr 2025 17:11:19 +0100 David Howells wrote:
> +	aead = crypto_krb5_prepare_encryption(krb5, &TK, RXGK_CLIENT_ENC_RESPONSE, gfp);
> +	if (IS_ERR(aead))
> +		goto aead_error;
> +	gk->resp_enc = aead;
> +
> +	if (crypto_aead_blocksize(gk->resp_enc) != krb5->block_len ||
> +	    crypto_aead_authsize(gk->resp_enc) != krb5->cksum_len) {
> +		pr_notice("algo inconsistent with krb5 table %u!=%u or %u!=%u\n",
> +			  crypto_aead_blocksize(gk->resp_enc), krb5->block_len,
> +			  crypto_aead_authsize(gk->resp_enc), krb5->cksum_len);
> +		return -EINVAL;

kfree_sensitive(buffer); missing?

> +	}
> +
> +	if (service) {
> +		switch (conn->security_level) {
> +		case RXRPC_SECURITY_AUTH:
> +			shash = crypto_krb5_prepare_checksum(
> +				krb5, &TK, RXGK_SERVER_MIC_PACKET, gfp);
> +			if (IS_ERR(shash))
> +				goto hash_error;
-- 
pw-bot: cr

Re: [PATCH net-next v2 06/13] rxrpc: rxgk: Provide infrastructure and key derivation

[David Howells]

Jakub Kicinski <kuba@kernel.org> wrote:

> On Mon,  7 Apr 2025 17:11:19 +0100 David Howells wrote:
> > +	aead = crypto_krb5_prepare_encryption(krb5, &TK, RXGK_CLIENT_ENC_RESPONSE, gfp);
> > +	if (IS_ERR(aead))
> > +		goto aead_error;
> > +	gk->resp_enc = aead;
> > +
> > +	if (crypto_aead_blocksize(gk->resp_enc) != krb5->block_len ||
> > +	    crypto_aead_authsize(gk->resp_enc) != krb5->cksum_len) {
> > +		pr_notice("algo inconsistent with krb5 table %u!=%u or %u!=%u\n",
> > +			  crypto_aead_blocksize(gk->resp_enc), krb5->block_len,
> > +			  crypto_aead_authsize(gk->resp_enc), krb5->cksum_len);
> > +		return -EINVAL;
> 
> kfree_sensitive(buffer); missing?

Good catch, thanks.  That path should never trigger, but it should really do
"ret = -EINVAL; goto out;".

Do you want me to respin the patches or follow up with a fix patch?

David

Re: [PATCH net-next v2 06/13] rxrpc: rxgk: Provide infrastructure and key derivation

[Jakub Kicinski]

On Thu, 10 Apr 2025 07:54:09 +0100 David Howells wrote:
> Good catch, thanks.  That path should never trigger, but it should really do
> "ret = -EINVAL; goto out;".
> 
> Do you want me to respin the patches or follow up with a fix patch?

Sorry for the delay. I was hoping you could respin and maybe fix/give
up on the annotation in patch 3? Right now patch 3 gets flagged as 
a build warning which terminates the CI processing before we get to
make htmldocs. And it would be nice to get that run given patch 1.

Re: [PATCH net-next v2 06/13] rxrpc: rxgk: Provide infrastructure and key derivation

[David Howells]

Jakub Kicinski <kuba@kernel.org> wrote:

> Sorry for the delay. I was hoping you could respin and maybe fix/give
> up on the annotation in patch 3? Right now patch 3 gets flagged as 
> a build warning which terminates the CI processing before we get to
> make htmldocs. And it would be nice to get that run given patch 1.

I can remove the annotation, but it may just move the warning to a different
place.

David

[PATCH net-next v2 07/13] rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)

[David Howells]

Implement the basic parts of the yfs-rxgk security class (security index 6)
to support GSSAPI-negotiated security.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
 Documentation/networking/rxrpc.rst |    1 +
 fs/afs/cm_security.c               |   12 +
 include/trace/events/rxrpc.h       |   45 +-
 net/rxrpc/Makefile                 |    2 +
 net/rxrpc/ar-internal.h            |   17 +
 net/rxrpc/output.c                 |    2 +-
 net/rxrpc/protocol.h               |   20 +
 net/rxrpc/rxgk.c                   | 1215 ++++++++++++++++++++++++++++
 net/rxrpc/rxgk_app.c               |  285 +++++++
 net/rxrpc/rxgk_common.h            |   91 +++
 net/rxrpc/rxkad.c                  |    6 +-
 net/rxrpc/security.c               |    3 +
 12 files changed, 1694 insertions(+), 5 deletions(-)
 create mode 100644 net/rxrpc/rxgk.c
 create mode 100644 net/rxrpc/rxgk_app.c

diff --git a/Documentation/networking/rxrpc.rst b/Documentation/networking/rxrpc.rst
index eb941b2577dd..a01f0c81ca4b 100644
--- a/Documentation/networking/rxrpc.rst
+++ b/Documentation/networking/rxrpc.rst
@@ -1182,6 +1182,7 @@ API Function Reference
 .. kernel-doc:: net/rxrpc/oob.c
 .. kernel-doc:: net/rxrpc/peer_object.c
 .. kernel-doc:: net/rxrpc/recvmsg.c
+.. kernel-doc:: net/rxrpc/rxgk.c
 .. kernel-doc:: net/rxrpc/rxkad.c
 .. kernel-doc:: net/rxrpc/sendmsg.c
 .. kernel-doc:: net/rxrpc/server_key.c
diff --git a/fs/afs/cm_security.c b/fs/afs/cm_security.c
index efe6a23c8477..e8eb63e4d124 100644
--- a/fs/afs/cm_security.c
+++ b/fs/afs/cm_security.c
@@ -6,6 +6,7 @@
  */
 
 #include <linux/slab.h>
+#include <crypto/krb5.h>
 #include "internal.h"
 #include "afs_fs.h"
 #include "protocol_yfs.h"
@@ -17,6 +18,9 @@
  */
 static int afs_respond_to_challenge(struct sk_buff *challenge)
 {
+#ifdef CONFIG_RXGK
+	struct krb5_buffer appdata = {};
+#endif
 	struct rxrpc_peer *peer;
 	unsigned long peer_data;
 	u16 service_id;
@@ -44,8 +48,16 @@ static int afs_respond_to_challenge(struct sk_buff *challenge)
 	}
 
 	switch (security_index) {
+#ifdef CONFIG_RXKAD
 	case RXRPC_SECURITY_RXKAD:
 		return rxkad_kernel_respond_to_challenge(challenge);
+#endif
+
+#ifdef CONFIG_RXGK
+	case RXRPC_SECURITY_RXGK:
+	case RXRPC_SECURITY_YFS_RXGK:
+		return rxgk_kernel_respond_to_challenge(challenge, &appdata);
+#endif
 
 	default:
 		return rxrpc_kernel_reject_challenge(challenge, RX_USER_ABORT, -EPROTO,
diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 08ecebd90595..aab81e8196ae 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -69,6 +69,38 @@
 	EM(rxkad_abort_resp_tkt_sname,		"rxkad-resp-tk-sname")	\
 	EM(rxkad_abort_resp_unknown_tkt,	"rxkad-resp-unknown-tkt") \
 	EM(rxkad_abort_resp_version,		"rxkad-resp-version")	\
+	/* RxGK security errors */					\
+	EM(rxgk_abort_1_verify_mic_eproto,	"rxgk1-vfy-mic-eproto")	\
+	EM(rxgk_abort_2_decrypt_eproto,		"rxgk2-dec-eproto")	\
+	EM(rxgk_abort_2_short_data,		"rxgk2-short-data")	\
+	EM(rxgk_abort_2_short_encdata,		"rxgk2-short-encdata")	\
+	EM(rxgk_abort_2_short_header,		"rxgk2-short-hdr")	\
+	EM(rxgk_abort_bad_key_number,		"rxgk-bad-key-num")	\
+	EM(rxgk_abort_chall_key_expired,	"rxgk-chall-key-exp")	\
+	EM(rxgk_abort_chall_no_key,		"rxgk-chall-nokey")	\
+	EM(rxgk_abort_chall_short,		"rxgk-chall-short")	\
+	EM(rxgk_abort_resp_auth_dec,		"rxgk-resp-auth-dec")	\
+	EM(rxgk_abort_resp_bad_callid,		"rxgk-resp-bad-callid")	\
+	EM(rxgk_abort_resp_bad_nonce,		"rxgk-resp-bad-nonce")	\
+	EM(rxgk_abort_resp_bad_param,		"rxgk-resp-bad-param")	\
+	EM(rxgk_abort_resp_call_ctr,		"rxgk-resp-call-ctr")	\
+	EM(rxgk_abort_resp_call_state,		"rxgk-resp-call-state")	\
+	EM(rxgk_abort_resp_internal_error,	"rxgk-resp-int-error")	\
+	EM(rxgk_abort_resp_nopkg,		"rxgk-resp-nopkg")	\
+	EM(rxgk_abort_resp_short_applen,	"rxgk-resp-short-applen") \
+	EM(rxgk_abort_resp_short_auth,		"rxgk-resp-short-auth") \
+	EM(rxgk_abort_resp_short_call_list,	"rxgk-resp-short-callls") \
+	EM(rxgk_abort_resp_short_packet,	"rxgk-resp-short-packet") \
+	EM(rxgk_abort_resp_short_yfs_klen,	"rxgk-resp-short-yfs-klen") \
+	EM(rxgk_abort_resp_short_yfs_key,	"rxgk-resp-short-yfs-key") \
+	EM(rxgk_abort_resp_short_yfs_tkt,	"rxgk-resp-short-yfs-tkt") \
+	EM(rxgk_abort_resp_tok_dec,		"rxgk-resp-tok-dec")	\
+	EM(rxgk_abort_resp_tok_internal_error,	"rxgk-resp-tok-int-err") \
+	EM(rxgk_abort_resp_tok_keyerr,		"rxgk-resp-tok-keyerr")	\
+	EM(rxgk_abort_resp_tok_nokey,		"rxgk-resp-tok-nokey")	\
+	EM(rxgk_abort_resp_tok_nopkg,		"rxgk-resp-tok-nopkg")	\
+	EM(rxgk_abort_resp_tok_short,		"rxgk-resp-tok-short")	\
+	EM(rxgk_abort_resp_xdr_align,		"rxgk-resp-xdr-align")	\
 	/* rxrpc errors */						\
 	EM(rxrpc_abort_call_improper_term,	"call-improper-term")	\
 	EM(rxrpc_abort_call_reset,		"call-reset")		\
@@ -471,6 +503,7 @@
 	EM(rxrpc_tx_point_call_final_resend,	"CallFinalResend") \
 	EM(rxrpc_tx_point_conn_abort,		"ConnAbort") \
 	EM(rxrpc_tx_point_reject,		"Reject") \
+	EM(rxrpc_tx_point_rxgk_challenge,	"RxGKChall") \
 	EM(rxrpc_tx_point_rxkad_challenge,	"RxkadChall") \
 	EM(rxrpc_tx_point_response,		"Response") \
 	EM(rxrpc_tx_point_version_keepalive,	"VerKeepalive") \
@@ -489,6 +522,7 @@
 
 #define rxrpc_txbuf_traces \
 	EM(rxrpc_txbuf_alloc_data,		"ALLOC DATA ")	\
+	EM(rxrpc_txbuf_alloc_response,		"ALLOC RESP ")	\
 	EM(rxrpc_txbuf_free,			"FREE       ")	\
 	EM(rxrpc_txbuf_get_buffer,		"GET BUFFER ")	\
 	EM(rxrpc_txbuf_get_trans,		"GET TRANS  ")	\
@@ -496,6 +530,7 @@
 	EM(rxrpc_txbuf_put_cleaned,		"PUT CLEANED")	\
 	EM(rxrpc_txbuf_put_nomem,		"PUT NOMEM  ")	\
 	EM(rxrpc_txbuf_put_rotated,		"PUT ROTATED")	\
+	EM(rxrpc_txbuf_put_response_tx,		"PUT RESP TX")	\
 	EM(rxrpc_txbuf_put_send_aborted,	"PUT SEND-X ")	\
 	EM(rxrpc_txbuf_put_trans,		"PUT TRANS  ")	\
 	EM(rxrpc_txbuf_see_lost,		"SEE LOST   ")	\
@@ -1178,6 +1213,7 @@ TRACE_EVENT(rxrpc_rx_challenge,
 		    __field(u32,		version)
 		    __field(u32,		nonce)
 		    __field(u32,		min_level)
+		    __field(u8,			security_ix)
 			     ),
 
 	    TP_fast_assign(
@@ -1186,11 +1222,13 @@ TRACE_EVENT(rxrpc_rx_challenge,
 		    __entry->version = version;
 		    __entry->nonce = nonce;
 		    __entry->min_level = min_level;
+		    __entry->security_ix = conn->security_ix;
 			   ),
 
-	    TP_printk("C=%08x CHALLENGE %08x v=%x n=%x ml=%x",
+	    TP_printk("C=%08x CHALLENGE r=%08x sx=%u v=%x n=%x ml=%x",
 		      __entry->conn,
 		      __entry->serial,
+		      __entry->security_ix,
 		      __entry->version,
 		      __entry->nonce,
 		      __entry->min_level)
@@ -1208,6 +1246,7 @@ TRACE_EVENT(rxrpc_rx_response,
 		    __field(u32,		version)
 		    __field(u32,		kvno)
 		    __field(u32,		ticket_len)
+		    __field(u8,			security_ix)
 			     ),
 
 	    TP_fast_assign(
@@ -1216,11 +1255,13 @@ TRACE_EVENT(rxrpc_rx_response,
 		    __entry->version = version;
 		    __entry->kvno = kvno;
 		    __entry->ticket_len = ticket_len;
+		    __entry->security_ix = conn->security_ix;
 			   ),
 
-	    TP_printk("C=%08x RESPONSE %08x v=%x kvno=%x tl=%x",
+	    TP_printk("C=%08x RESPONSE r=%08x sx=%u v=%x kvno=%x tl=%x",
 		      __entry->conn,
 		      __entry->serial,
+		      __entry->security_ix,
 		      __entry->version,
 		      __entry->kvno,
 		      __entry->ticket_len)
diff --git a/net/rxrpc/Makefile b/net/rxrpc/Makefile
index 3eda77a0266b..c0542bae719e 100644
--- a/net/rxrpc/Makefile
+++ b/net/rxrpc/Makefile
@@ -41,6 +41,8 @@ rxrpc-$(CONFIG_PROC_FS) += proc.o
 rxrpc-$(CONFIG_RXKAD) += rxkad.o
 rxrpc-$(CONFIG_SYSCTL) += sysctl.o
 rxrpc-$(CONFIG_RXGK) += \
+	rxgk.o \
+	rxgk_app.o \
 	rxgk_kdf.o
 
 obj-$(CONFIG_RXPERF) += rxperf.o
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 81bacac94430..c8d66a02c8fe 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -31,6 +31,7 @@ struct key_preparsed_payload;
 struct rxrpc_connection;
 struct rxrpc_txbuf;
 struct rxrpc_txqueue;
+struct rxgk_context;
 
 /*
  * Mark applied to socket buffers in skb->mark.  skb->priority is used
@@ -312,6 +313,11 @@ struct rxrpc_security {
 
 	/* clear connection security */
 	void (*clear)(struct rxrpc_connection *);
+
+	/* Default ticket -> key decoder */
+	int (*default_decode_ticket)(struct rxrpc_connection *conn, struct sk_buff *skb,
+				     unsigned int ticket_offset, unsigned int ticket_len,
+				     struct key **_key);
 };
 
 /*
@@ -559,7 +565,10 @@ struct rxrpc_connection {
 			u32	nonce;		/* response re-use preventer */
 		} rxkad;
 		struct {
+			struct rxgk_context *keys[1];
 			u64	start_time;	/* The start time for TK derivation */
+			u8	nonce[20];	/* Response re-use preventer */
+			u32	enctype;	/* Kerberos 5 encoding type */
 		} rxgk;
 	};
 	struct sk_buff		*tx_response;	/* Response packet to be transmitted */
@@ -903,6 +912,8 @@ struct rxrpc_txbuf {
 	unsigned short		len;		/* Amount of data in buffer */
 	unsigned short		space;		/* Remaining data space */
 	unsigned short		offset;		/* Offset of fill point */
+	unsigned short		crypto_header;	/* Size of crypto header */
+	unsigned short		sec_header;	/* Size of security header */
 	unsigned short		pkt_len;	/* Size of packet content */
 	unsigned short		alloc_size;	/* Amount of bufferage allocated */
 	unsigned int		flags;
@@ -1337,6 +1348,7 @@ int rxrpc_sendmsg_oob(struct rxrpc_sock *rx, struct msghdr *msg, size_t len);
 /*
  * output.c
  */
+ssize_t do_udp_sendmsg(struct socket *socket, struct msghdr *msg, size_t len);
 void rxrpc_send_ACK(struct rxrpc_call *call, u8 ack_reason,
 		    rxrpc_serial_t serial, enum rxrpc_propose_ack_trace why);
 void rxrpc_send_probe_for_pmtud(struct rxrpc_call *call);
@@ -1409,6 +1421,11 @@ void rxrpc_call_add_rtt(struct rxrpc_call *call, enum rxrpc_rtt_rx_trace why,
 ktime_t rxrpc_get_rto_backoff(struct rxrpc_call *call, bool retrans);
 void rxrpc_call_init_rtt(struct rxrpc_call *call);
 
+/*
+ * rxgk.c
+ */
+extern const struct rxrpc_security rxgk_yfs;
+
 /*
  * rxkad.c
  */
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 04c900990a40..8138f35d7945 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -18,7 +18,7 @@
 
 extern int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len);
 
-static ssize_t do_udp_sendmsg(struct socket *socket, struct msghdr *msg, size_t len)
+ssize_t do_udp_sendmsg(struct socket *socket, struct msghdr *msg, size_t len)
 {
 	struct sockaddr *sa = msg->msg_name;
 	struct sock *sk = socket->sk;
diff --git a/net/rxrpc/protocol.h b/net/rxrpc/protocol.h
index 42f70e4636f8..f8bfec12bc7e 100644
--- a/net/rxrpc/protocol.h
+++ b/net/rxrpc/protocol.h
@@ -181,4 +181,24 @@ struct rxkad_response {
 	__be32		ticket_len;	/* Kerberos ticket length  */
 } __packed;
 
+/*
+ * GSSAPI security type-4 and type-6 data header.
+ */
+struct rxgk_header {
+	__be32	epoch;
+	__be32	cid;
+	__be32	call_number;
+	__be32	seq;
+	__be32	sec_index;
+	__be32	data_len;
+} __packed;
+
+/*
+ * GSSAPI security type-4 and type-6 response packet header.
+ */
+struct rxgk_response {
+	__be64	start_time;
+	__be32	token_len;
+} __packed;
+
 #endif /* _LINUX_RXRPC_PACKET_H */
diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
new file mode 100644
index 000000000000..02752eeb2395
--- /dev/null
+++ b/net/rxrpc/rxgk.c
@@ -0,0 +1,1215 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* GSSAPI-based RxRPC security
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/key-type.h>
+#include "ar-internal.h"
+#include "rxgk_common.h"
+
+/*
+ * Parse the information from a server key
+ */
+static int rxgk_preparse_server_key(struct key_preparsed_payload *prep)
+{
+	const struct krb5_enctype *krb5;
+	struct krb5_buffer *server_key = (void *)&prep->payload.data[2];
+	unsigned int service, sec_class, kvno, enctype;
+	int n = 0;
+
+	_enter("%zu", prep->datalen);
+
+	if (sscanf(prep->orig_description, "%u:%u:%u:%u%n",
+		   &service, &sec_class, &kvno, &enctype, &n) != 4)
+		return -EINVAL;
+
+	if (prep->orig_description[n])
+		return -EINVAL;
+
+	krb5 = crypto_krb5_find_enctype(enctype);
+	if (!krb5)
+		return -ENOPKG;
+
+	prep->payload.data[0] = (struct krb5_enctype *)krb5;
+
+	if (prep->datalen != krb5->key_len)
+		return -EKEYREJECTED;
+
+	server_key->len = prep->datalen;
+	server_key->data = kmemdup(prep->data, prep->datalen, GFP_KERNEL);
+	if (!server_key->data)
+		return -ENOMEM;
+
+	_leave(" = 0");
+	return 0;
+}
+
+static void rxgk_free_server_key(union key_payload *payload)
+{
+	struct krb5_buffer *server_key = (void *)&payload->data[2];
+
+	kfree_sensitive(server_key->data);
+}
+
+static void rxgk_free_preparse_server_key(struct key_preparsed_payload *prep)
+{
+	rxgk_free_server_key(&prep->payload);
+}
+
+static void rxgk_destroy_server_key(struct key *key)
+{
+	rxgk_free_server_key(&key->payload);
+}
+
+static void rxgk_describe_server_key(const struct key *key, struct seq_file *m)
+{
+	const struct krb5_enctype *krb5 = key->payload.data[0];
+
+	if (krb5)
+		seq_printf(m, ": %s", krb5->name);
+}
+
+static struct rxgk_context *rxgk_get_key(struct rxrpc_connection *conn,
+					 u16 *specific_key_number)
+{
+	refcount_inc(&conn->rxgk.keys[0]->usage);
+	return conn->rxgk.keys[0];
+}
+
+/*
+ * initialise connection security
+ */
+static int rxgk_init_connection_security(struct rxrpc_connection *conn,
+					 struct rxrpc_key_token *token)
+{
+	struct rxgk_context *gk;
+	int ret;
+
+	_enter("{%d},{%x}", conn->debug_id, key_serial(conn->key));
+
+	conn->security_ix = token->security_index;
+	conn->security_level = token->rxgk->level;
+
+	if (rxrpc_conn_is_client(conn)) {
+		conn->rxgk.start_time = ktime_get();
+		do_div(conn->rxgk.start_time, 100);
+	}
+
+	gk = rxgk_generate_transport_key(conn, token->rxgk, 0, GFP_NOFS);
+	if (IS_ERR(gk))
+		return PTR_ERR(gk);
+	conn->rxgk.enctype = gk->krb5->etype;
+	conn->rxgk.keys[0] = gk;
+
+	switch (conn->security_level) {
+	case RXRPC_SECURITY_PLAIN:
+	case RXRPC_SECURITY_AUTH:
+	case RXRPC_SECURITY_ENCRYPT:
+		break;
+	default:
+		ret = -EKEYREJECTED;
+		goto error;
+	}
+
+	ret = 0;
+error:
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Clean up the crypto on a call.
+ */
+static void rxgk_free_call_crypto(struct rxrpc_call *call)
+{
+}
+
+/*
+ * Work out how much data we can put in a packet.
+ */
+static struct rxrpc_txbuf *rxgk_alloc_txbuf(struct rxrpc_call *call, size_t remain, gfp_t gfp)
+{
+	enum krb5_crypto_mode mode;
+	struct rxgk_context *gk;
+	struct rxrpc_txbuf *txb;
+	size_t shdr, alloc, limit, part, offset, gap;
+
+	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 = 0;
+		mode = KRB5_CHECKSUM_MODE;
+		break;
+	case RXRPC_SECURITY_ENCRYPT:
+		shdr = sizeof(struct rxgk_header);
+		mode = KRB5_ENCRYPT_MODE;
+		break;
+	}
+
+	gk = rxgk_get_key(call->conn, NULL);
+	if (IS_ERR(gk))
+		return NULL;
+
+	/* Work out the maximum amount of data that will fit. */
+	alloc = RXRPC_JUMBO_DATALEN;
+	limit = crypto_krb5_how_much_data(gk->krb5, mode, &alloc, &offset);
+
+	if (remain < limit - shdr) {
+		part = remain;
+		alloc = crypto_krb5_how_much_buffer(gk->krb5, mode,
+						    shdr + part, &offset);
+		gap = 0;
+	} else {
+		part = limit - shdr;
+		gap = RXRPC_JUMBO_DATALEN - alloc;
+		alloc = RXRPC_JUMBO_DATALEN;
+	}
+
+	rxgk_put(gk);
+
+	txb = rxrpc_alloc_data_txbuf(call, alloc, 16, gfp);
+	if (!txb)
+		return NULL;
+
+	txb->crypto_header	= offset;
+	txb->sec_header		= shdr;
+	txb->offset		+= offset + shdr;
+	txb->space		= part;
+
+	/* Clear excess space in the packet */
+	if (gap)
+		memset(txb->data + alloc - gap, 0, gap);
+	return txb;
+}
+
+/*
+ * Integrity mode (sign a packet - level 1 security)
+ */
+static int rxgk_secure_packet_integrity(const struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct rxrpc_txbuf *txb)
+{
+	struct rxgk_header *hdr;
+	struct scatterlist sg[1];
+	struct krb5_buffer metadata;
+	int ret = -ENOMEM;
+
+	_enter("");
+
+	hdr = kzalloc(sizeof(*hdr), GFP_NOFS);
+	if (!hdr)
+		goto error_gk;
+
+	hdr->epoch	= htonl(call->conn->proto.epoch);
+	hdr->cid	= htonl(call->cid);
+	hdr->call_number = htonl(call->call_id);
+	hdr->seq	= htonl(txb->seq);
+	hdr->sec_index	= htonl(call->security_ix);
+	hdr->data_len	= htonl(txb->len);
+	metadata.len = sizeof(*hdr);
+	metadata.data = hdr;
+
+	sg_init_table(sg, 1);
+	sg_set_buf(&sg[0], txb->data, txb->alloc_size);
+
+	ret = crypto_krb5_get_mic(gk->krb5, gk->tx_Kc, &metadata,
+				  sg, 1, txb->alloc_size,
+				  txb->crypto_header, txb->sec_header + txb->len);
+	if (ret >= 0) {
+		txb->pkt_len = ret;
+		if (txb->alloc_size == RXRPC_JUMBO_DATALEN)
+			txb->jumboable = true;
+		gk->bytes_remaining -= ret;
+	}
+	kfree(hdr);
+error_gk:
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * wholly encrypt a packet (level 2 security)
+ */
+static int rxgk_secure_packet_encrypted(const struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct rxrpc_txbuf *txb)
+{
+	struct rxgk_header *hdr;
+	struct scatterlist sg[1];
+	int ret;
+
+	_enter("%x", txb->len);
+
+	/* Insert the header into the buffer. */
+	hdr = txb->data + txb->crypto_header;
+	hdr->epoch	 = htonl(call->conn->proto.epoch);
+	hdr->cid	 = htonl(call->cid);
+	hdr->call_number = htonl(call->call_id);
+	hdr->seq	 = htonl(txb->seq);
+	hdr->sec_index	 = htonl(call->security_ix);
+	hdr->data_len	 = htonl(txb->len);
+
+	sg_init_table(sg, 1);
+	sg_set_buf(&sg[0], txb->data, txb->alloc_size);
+
+	ret = crypto_krb5_encrypt(gk->krb5, gk->tx_enc,
+				  sg, 1, txb->alloc_size,
+				  txb->crypto_header, txb->sec_header + txb->len,
+				  false);
+	if (ret >= 0) {
+		txb->pkt_len = ret;
+		if (txb->alloc_size == RXRPC_JUMBO_DATALEN)
+			txb->jumboable = true;
+		gk->bytes_remaining -= ret;
+	}
+
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * checksum an RxRPC packet header
+ */
+static int rxgk_secure_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
+{
+	struct rxgk_context *gk;
+	int ret;
+
+	_enter("{%d{%x}},{#%u},%u,",
+	       call->debug_id, key_serial(call->conn->key), txb->seq, txb->len);
+
+	gk = rxgk_get_key(call->conn, NULL);
+	if (IS_ERR(gk))
+		return PTR_ERR(gk) == -ESTALE ? -EKEYREJECTED : PTR_ERR(gk);
+
+	ret = key_validate(call->conn->key);
+	if (ret < 0)
+		return ret;
+
+	txb->cksum = htons(gk->key_number);
+
+	switch (call->conn->security_level) {
+	case RXRPC_SECURITY_PLAIN:
+		rxgk_put(gk);
+		txb->pkt_len = txb->len;
+		return 0;
+	case RXRPC_SECURITY_AUTH:
+		return rxgk_secure_packet_integrity(call, gk, txb);
+	case RXRPC_SECURITY_ENCRYPT:
+		return rxgk_secure_packet_encrypted(call, gk, txb);
+	default:
+		rxgk_put(gk);
+		return -EPERM;
+	}
+}
+
+/*
+ * Integrity mode (check the signature on a packet - level 1 security)
+ */
+static int rxgk_verify_packet_integrity(struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_header *hdr;
+	struct krb5_buffer metadata;
+	unsigned int offset = sp->offset, len = sp->len;
+	size_t data_offset = 0, data_len = len;
+	u32 ac;
+	int ret = -ENOMEM;
+
+	_enter("");
+
+	crypto_krb5_where_is_the_data(gk->krb5, KRB5_CHECKSUM_MODE,
+				      &data_offset, &data_len);
+
+	hdr = kzalloc(sizeof(*hdr), GFP_NOFS);
+	if (!hdr)
+		return -ENOMEM;
+
+	hdr->epoch	= htonl(call->conn->proto.epoch);
+	hdr->cid	= htonl(call->cid);
+	hdr->call_number = htonl(call->call_id);
+	hdr->seq	= htonl(sp->hdr.seq);
+	hdr->sec_index	= htonl(call->security_ix);
+	hdr->data_len	= htonl(data_len);
+
+	metadata.len = sizeof(*hdr);
+	metadata.data = hdr;
+	ret = rxgk_verify_mic_skb(gk->krb5, gk->rx_Kc, &metadata,
+				  skb, &offset, &len, &ac);
+	kfree(hdr);
+	if (ret == -EPROTO) {
+		rxrpc_abort_eproto(call, skb, ac,
+				   rxgk_abort_1_verify_mic_eproto);
+	} else {
+		sp->offset = offset;
+		sp->len = len;
+	}
+
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Decrypt an encrypted packet (level 2 security).
+ */
+static int rxgk_verify_packet_encrypted(struct rxrpc_call *call,
+					struct rxgk_context *gk,
+					struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_header hdr;
+	unsigned int offset = sp->offset, len = sp->len;
+	int ret;
+	u32 ac;
+
+	_enter("");
+
+	ret = rxgk_decrypt_skb(gk->krb5, gk->rx_enc, skb, &offset, &len, &ac);
+	if (ret == -EPROTO)
+		rxrpc_abort_eproto(call, skb, ac, rxgk_abort_2_decrypt_eproto);
+	if (ret < 0)
+		goto error;
+
+	if (len < sizeof(hdr)) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+					 rxgk_abort_2_short_header);
+		goto error;
+	}
+
+	/* Extract the header from the skb */
+	ret = skb_copy_bits(skb, offset, &hdr, sizeof(hdr));
+	if (ret < 0) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+					 rxgk_abort_2_short_encdata);
+		goto error;
+	}
+	offset += sizeof(hdr);
+	len -= sizeof(hdr);
+
+	if (ntohl(hdr.epoch)		!= call->conn->proto.epoch ||
+	    ntohl(hdr.cid)		!= call->cid ||
+	    ntohl(hdr.call_number)	!= call->call_id ||
+	    ntohl(hdr.seq)		!= sp->hdr.seq ||
+	    ntohl(hdr.sec_index)	!= call->security_ix ||
+	    ntohl(hdr.data_len)		> len) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_SEALEDINCON,
+					 rxgk_abort_2_short_data);
+		goto error;
+	}
+
+	sp->offset = offset;
+	sp->len = ntohl(hdr.data_len);
+	ret = 0;
+error:
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Verify the security on a received packet or subpacket (if part of a
+ * jumbo packet).
+ */
+static int rxgk_verify_packet(struct rxrpc_call *call, struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_context *gk;
+	u16 key_number = sp->hdr.cksum;
+
+	_enter("{%d{%x}},{#%u}",
+	       call->debug_id, key_serial(call->conn->key), sp->hdr.seq);
+
+	gk = rxgk_get_key(call->conn, &key_number);
+	if (IS_ERR(gk)) {
+		switch (PTR_ERR(gk)) {
+		case -ESTALE:
+			return rxrpc_abort_eproto(call, skb, RXGK_BADKEYNO,
+						  rxgk_abort_bad_key_number);
+		default:
+			return PTR_ERR(gk);
+		}
+	}
+
+	switch (call->conn->security_level) {
+	case RXRPC_SECURITY_PLAIN:
+		return 0;
+	case RXRPC_SECURITY_AUTH:
+		return rxgk_verify_packet_integrity(call, gk, skb);
+	case RXRPC_SECURITY_ENCRYPT:
+		return rxgk_verify_packet_encrypted(call, gk, skb);
+	default:
+		rxgk_put(gk);
+		return -ENOANO;
+	}
+}
+
+/*
+ * Allocate memory to hold a challenge or a response packet.  We're not running
+ * in the io_thread, so we can't use ->tx_alloc.
+ */
+static struct page *rxgk_alloc_packet(size_t total_len)
+{
+	gfp_t gfp = GFP_NOFS;
+	int order;
+
+	order = get_order(total_len);
+	if (order > 0)
+		gfp |= __GFP_COMP;
+	return alloc_pages(gfp, order);
+}
+
+/*
+ * Issue a challenge.
+ */
+static int rxgk_issue_challenge(struct rxrpc_connection *conn)
+{
+	struct rxrpc_wire_header *whdr;
+	struct bio_vec bvec[1];
+	struct msghdr msg;
+	struct page *page;
+	size_t len = sizeof(*whdr) + sizeof(conn->rxgk.nonce);
+	u32 serial;
+	int ret;
+
+	_enter("{%d}", conn->debug_id);
+
+	get_random_bytes(&conn->rxgk.nonce, sizeof(conn->rxgk.nonce));
+
+	/* We can't use conn->tx_alloc without a lock */
+	page = rxgk_alloc_packet(sizeof(*whdr) + sizeof(conn->rxgk.nonce));
+	if (!page)
+		return -ENOMEM;
+
+	bvec_set_page(&bvec[0], page, len, 0);
+	iov_iter_bvec(&msg.msg_iter, WRITE, bvec, 1, len);
+
+	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	= MSG_SPLICE_PAGES;
+
+	whdr = page_address(page);
+	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);
+
+	memcpy(whdr + 1, conn->rxgk.nonce, sizeof(conn->rxgk.nonce));
+
+	serial = rxrpc_get_next_serials(conn, 1);
+	whdr->serial = htonl(serial);
+
+	ret = do_udp_sendmsg(conn->local->socket, &msg, len);
+	if (ret > 0)
+		conn->peer->last_tx_at = ktime_get_seconds();
+	__free_page(page);
+
+	if (ret < 0) {
+		trace_rxrpc_tx_fail(conn->debug_id, serial, ret,
+				    rxrpc_tx_point_rxgk_challenge);
+		return -EAGAIN;
+	}
+
+	trace_rxrpc_tx_packet(conn->debug_id, whdr,
+			      rxrpc_tx_point_rxgk_challenge);
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * Validate a challenge packet.
+ */
+static bool rxgk_validate_challenge(struct rxrpc_connection *conn,
+				    struct sk_buff *skb)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	u8 nonce[20];
+
+	if (!conn->key) {
+		rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
+				 rxgk_abort_chall_no_key);
+		return false;
+	}
+
+	if (key_validate(conn->key) < 0) {
+		rxrpc_abort_conn(conn, skb, RXGK_EXPIRED, -EPROTO,
+				 rxgk_abort_chall_key_expired);
+		return false;
+	}
+
+	if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
+			  nonce, sizeof(nonce)) < 0) {
+		rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+				 rxgk_abort_chall_short);
+		return false;
+	}
+
+	trace_rxrpc_rx_challenge(conn, sp->hdr.serial, 0, *(u32 *)nonce, 0);
+	return true;
+}
+
+/**
+ * rxgk_kernel_query_challenge - Query RxGK-specific challenge parameters
+ * @challenge: The challenge packet to query
+ *
+ * Return: The Kerberos 5 encoding type for the challenged connection.
+ */
+u32 rxgk_kernel_query_challenge(struct sk_buff *challenge)
+{
+	struct rxrpc_skb_priv *sp = rxrpc_skb(challenge);
+
+	return sp->chall.conn->rxgk.enctype;
+}
+EXPORT_SYMBOL(rxgk_kernel_query_challenge);
+
+/*
+ * Fill out the control message to pass to userspace to inform about the
+ * challenge.
+ */
+static int rxgk_challenge_to_recvmsg(struct rxrpc_connection *conn,
+				     struct sk_buff *challenge,
+				     struct msghdr *msg)
+{
+	struct rxgk_challenge chall;
+
+	chall.base.service_id		= conn->service_id;
+	chall.base.security_index	= conn->security_ix;
+	chall.enctype			= conn->rxgk.enctype;
+
+	return put_cmsg(msg, SOL_RXRPC, RXRPC_CHALLENGED, sizeof(chall), &chall);
+}
+
+/*
+ * Insert the requisite amount of XDR padding for the length given.
+ */
+static int rxgk_pad_out(struct sk_buff *response, size_t len, size_t offset)
+{
+	__be32 zero = 0;
+	size_t pad = xdr_round_up(len) - len;
+	int ret;
+
+	if (!pad)
+		return 0;
+
+	ret = skb_store_bits(response, offset, &zero, pad);
+	if (ret < 0)
+		return ret;
+	return pad;
+}
+
+/*
+ * Insert the header into the response.
+ */
+static noinline ssize_t rxgk_insert_response_header(struct rxrpc_connection *conn,
+						    struct rxgk_context *gk,
+						    struct sk_buff *response,
+						    size_t offset)
+{
+	struct rxrpc_skb_priv *rsp = rxrpc_skb(response);
+
+	struct {
+		struct rxrpc_wire_header whdr;
+		__be32 start_time_msw;
+		__be32 start_time_lsw;
+		__be32 ticket_len;
+	} h;
+	int ret;
+
+	rsp->resp.kvno		= gk->key_number;
+	rsp->resp.version	= gk->krb5->etype;
+
+	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		= htons(gk->key_number);
+	h.whdr.serviceId	= htons(conn->service_id);
+	h.start_time_msw	= htonl(upper_32_bits(conn->rxgk.start_time));
+	h.start_time_lsw	= htonl(lower_32_bits(conn->rxgk.start_time));
+	h.ticket_len		= htonl(gk->key->ticket.len);
+
+	ret = skb_store_bits(response, offset, &h, sizeof(h));
+	return ret < 0 ? ret : sizeof(h);
+}
+
+/*
+ * Construct the authenticator to go in the response packet
+ *
+ * struct RXGK_Authenticator {
+ *	opaque nonce[20];
+ *	opaque appdata<>;
+ *	RXGK_Level level;
+ *	unsigned int epoch;
+ *	unsigned int cid;
+ *	unsigned int call_numbers<>;
+ * };
+ */
+static ssize_t rxgk_construct_authenticator(struct rxrpc_connection *conn,
+					    struct sk_buff *challenge,
+					    const struct krb5_buffer *appdata,
+					    struct sk_buff *response,
+					    size_t offset)
+{
+	struct {
+		u8	nonce[20];
+		__be32	appdata_len;
+	} a;
+	struct {
+		__be32	level;
+		__be32	epoch;
+		__be32	cid;
+		__be32	call_numbers_count;
+		__be32	call_numbers[4];
+	} b;
+	int ret;
+
+	ret = skb_copy_bits(challenge, sizeof(struct rxrpc_wire_header),
+			    a.nonce, sizeof(a.nonce));
+	if (ret < 0)
+		return -EPROTO;
+
+	a.appdata_len = htonl(appdata->len);
+
+	ret = skb_store_bits(response, offset, &a, sizeof(a));
+	if (ret < 0)
+		return ret;
+	offset += sizeof(a);
+
+	if (appdata->len) {
+		ret = skb_store_bits(response, offset, appdata->data, appdata->len);
+		if (ret < 0)
+			return ret;
+		offset += appdata->len;
+
+		ret = rxgk_pad_out(response, appdata->len, offset);
+		if (ret < 0)
+			return ret;
+		offset += ret;
+	}
+
+	b.level			= htonl(conn->security_level);
+	b.epoch			= htonl(conn->proto.epoch);
+	b.cid			= htonl(conn->proto.cid);
+	b.call_numbers_count	= htonl(4);
+	b.call_numbers[0]	= htonl(conn->channels[0].call_counter);
+	b.call_numbers[1]	= htonl(conn->channels[1].call_counter);
+	b.call_numbers[2]	= htonl(conn->channels[2].call_counter);
+	b.call_numbers[3]	= htonl(conn->channels[3].call_counter);
+
+	ret = skb_store_bits(response, offset, &b, sizeof(b));
+	if (ret < 0)
+		return ret;
+	return sizeof(a) + xdr_round_up(appdata->len) + sizeof(b);
+}
+
+static ssize_t rxgk_encrypt_authenticator(struct rxrpc_connection *conn,
+					  struct rxgk_context *gk,
+					  struct sk_buff *response,
+					  size_t offset,
+					  size_t alloc_len,
+					  size_t auth_offset,
+					  size_t auth_len)
+{
+	struct scatterlist sg[16];
+	int nr_sg;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	nr_sg = skb_to_sgvec(response, sg, offset, alloc_len);
+	if (unlikely(nr_sg < 0))
+		return nr_sg;
+	return crypto_krb5_encrypt(gk->krb5, gk->resp_enc, sg, nr_sg, alloc_len,
+				   auth_offset, auth_len, false);
+}
+
+/*
+ * Construct the response.
+ *
+ * struct RXGK_Response {
+ *	rxgkTime start_time;
+ *	RXGK_Data token;
+ *	opaque authenticator<RXGK_MAXAUTHENTICATOR>
+ * };
+ */
+static int rxgk_construct_response(struct rxrpc_connection *conn,
+				   struct sk_buff *challenge,
+				   struct krb5_buffer *appdata)
+{
+	struct rxrpc_skb_priv *csp, *rsp;
+	struct rxgk_context *gk;
+	struct sk_buff *response;
+	size_t len, auth_len, authx_len, offset, auth_offset, authx_offset;
+	__be32 tmp;
+	int ret;
+
+	gk = rxgk_get_key(conn, NULL);
+	if (IS_ERR(gk))
+		return PTR_ERR(gk);
+
+	auth_len = 20 + (4 + appdata->len) + 12 + (1 + 4) * 4;
+	authx_len = crypto_krb5_how_much_buffer(gk->krb5, KRB5_ENCRYPT_MODE,
+						auth_len, &auth_offset);
+	len = sizeof(struct rxrpc_wire_header) +
+		8 + (4 + xdr_round_up(gk->key->ticket.len)) + (4 + authx_len);
+
+	response = alloc_skb_with_frags(0, len, 0, &ret, GFP_NOFS);
+	if (!response)
+		goto error;
+	rxrpc_new_skb(response, rxrpc_skb_new_response_rxgk);
+	response->len = len;
+	response->data_len = len;
+
+	ret = rxgk_insert_response_header(conn, gk, response, 0);
+	if (ret < 0)
+		goto error;
+	offset = ret;
+
+	ret = skb_store_bits(response, offset, gk->key->ticket.data, gk->key->ticket.len);
+	if (ret < 0)
+		goto error;
+	offset += gk->key->ticket.len;
+	ret = rxgk_pad_out(response, gk->key->ticket.len, offset);
+	if (ret < 0)
+		goto error;
+
+	authx_offset = offset + ret + 4; /* Leave a gap for the length. */
+
+	ret = rxgk_construct_authenticator(conn, challenge, appdata, response,
+					   authx_offset + auth_offset);
+	if (ret < 0)
+		goto error;
+	auth_len = ret;
+
+	ret = rxgk_encrypt_authenticator(conn, gk, response,
+					 authx_offset, authx_len,
+					 auth_offset, auth_len);
+	if (ret < 0)
+		goto error;
+	authx_len = ret;
+
+	tmp = htonl(authx_len);
+	ret = skb_store_bits(response, authx_offset - 4, &tmp, 4);
+	if (ret < 0)
+		goto error;
+
+	ret = rxgk_pad_out(response, authx_len, authx_offset + authx_len);
+	if (ret < 0)
+		return ret;
+	len = authx_offset + authx_len + ret;
+
+	if (len != response->len) {
+		response->len = len;
+		response->data_len = len;
+	}
+
+	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);
+	rxgk_put(gk);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Respond to a challenge packet.
+ */
+static int rxgk_respond_to_challenge(struct rxrpc_connection *conn,
+				     struct sk_buff *challenge,
+				     struct krb5_buffer *appdata)
+{
+	_enter("{%d,%x}", conn->debug_id, key_serial(conn->key));
+
+	if (key_validate(conn->key) < 0)
+		return rxrpc_abort_conn(conn, NULL, RXGK_EXPIRED, -EPROTO,
+					rxgk_abort_chall_key_expired);
+
+	return rxgk_construct_response(conn, challenge, appdata);
+}
+
+static int rxgk_respond_to_challenge_no_appdata(struct rxrpc_connection *conn,
+						struct sk_buff *challenge)
+{
+	struct krb5_buffer appdata = {};
+
+	return rxgk_respond_to_challenge(conn, challenge, &appdata);
+}
+
+/**
+ * rxgk_kernel_respond_to_challenge - Respond to a challenge with appdata
+ * @challenge: The challenge to respond to
+ * @appdata: The application data to include in the RESPONSE authenticator
+ *
+ * Allow a kernel application to respond to a CHALLENGE with application data
+ * to be included in the RxGK RESPONSE Authenticator.
+ *
+ * Return: %0 if successful and a negative error code otherwise.
+ */
+int rxgk_kernel_respond_to_challenge(struct sk_buff *challenge,
+				     struct krb5_buffer *appdata)
+{
+	struct rxrpc_skb_priv *csp = rxrpc_skb(challenge);
+
+	return rxgk_respond_to_challenge(csp->chall.conn, challenge, appdata);
+}
+EXPORT_SYMBOL(rxgk_kernel_respond_to_challenge);
+
+/*
+ * Parse sendmsg() control message and respond to challenge.  We need to see if
+ * there's an appdata to fish out.
+ */
+static int rxgk_sendmsg_respond_to_challenge(struct sk_buff *challenge,
+					     struct msghdr *msg)
+{
+	struct krb5_buffer appdata = {};
+	struct cmsghdr *cmsg;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (cmsg->cmsg_level != SOL_RXRPC ||
+		    cmsg->cmsg_type != RXRPC_RESP_RXGK_APPDATA)
+			continue;
+		if (appdata.data)
+			return -EINVAL;
+		appdata.data = CMSG_DATA(cmsg);
+		appdata.len = cmsg->cmsg_len - sizeof(struct cmsghdr);
+	}
+
+	return rxgk_kernel_respond_to_challenge(challenge, &appdata);
+}
+
+/*
+ * Verify the authenticator.
+ *
+ * struct RXGK_Authenticator {
+ *	opaque nonce[20];
+ *	opaque appdata<>;
+ *	RXGK_Level level;
+ *	unsigned int epoch;
+ *	unsigned int cid;
+ *	unsigned int call_numbers<>;
+ * };
+ */
+static int rxgk_do_verify_authenticator(struct rxrpc_connection *conn,
+					const struct krb5_enctype *krb5,
+					struct sk_buff *skb,
+					__be32 *p, __be32 *end)
+{
+	u32 app_len, call_count, level, epoch, cid, i;
+
+	_enter("");
+
+	if (memcmp(p, conn->rxgk.nonce, 20) != 0)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_bad_nonce);
+	p += 20 / sizeof(__be32);
+
+	app_len	= ntohl(*p++);
+	if (app_len > (end - p) * sizeof(__be32))
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_applen);
+
+	p += xdr_round_up(app_len) / sizeof(__be32);
+	if (end - p < 4)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_applen);
+
+	level	= ntohl(*p++);
+	epoch	= ntohl(*p++);
+	cid	= ntohl(*p++);
+	call_count = ntohl(*p++);
+
+	if (level	!= conn->security_level ||
+	    epoch	!= conn->proto.epoch ||
+	    cid		!= conn->proto.cid ||
+	    call_count	> 4)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_bad_param);
+
+	if (end - p < call_count)
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+					rxgk_abort_resp_short_call_list);
+
+	for (i = 0; i < call_count; i++) {
+		u32 call_id = ntohl(*p++);
+
+		if (call_id > INT_MAX)
+			return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+						rxgk_abort_resp_bad_callid);
+
+		if (call_id < conn->channels[i].call_counter)
+			return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+						rxgk_abort_resp_call_ctr);
+
+		if (call_id > conn->channels[i].call_counter) {
+			if (conn->channels[i].call)
+				return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+							rxgk_abort_resp_call_state);
+
+			conn->channels[i].call_counter = call_id;
+		}
+	}
+
+	_leave(" = 0");
+	return 0;
+}
+
+/*
+ * Extract the authenticator and verify it.
+ */
+static int rxgk_verify_authenticator(struct rxrpc_connection *conn,
+				     const struct krb5_enctype *krb5,
+				     struct sk_buff *skb,
+				     unsigned int auth_offset, unsigned int auth_len)
+{
+	void *auth;
+	__be32 *p;
+	int ret;
+
+	auth = kmalloc(auth_len, GFP_NOFS);
+	if (!auth)
+		return -ENOMEM;
+
+	ret = skb_copy_bits(skb, auth_offset, auth, auth_len);
+	if (ret < 0) {
+		ret = rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EPROTO,
+				       rxgk_abort_resp_short_auth);
+		goto error;
+	}
+
+	p = auth;
+	ret = rxgk_do_verify_authenticator(conn, krb5, skb, p, p + auth_len);
+error:
+	kfree(auth);
+	return ret;
+}
+
+/*
+ * Verify a response.
+ *
+ * struct RXGK_Response {
+ *	rxgkTime	start_time;
+ *	RXGK_Data	token;
+ *	opaque		authenticator<RXGK_MAXAUTHENTICATOR>
+ * };
+ */
+static int rxgk_verify_response(struct rxrpc_connection *conn,
+				struct sk_buff *skb)
+{
+	const struct krb5_enctype *krb5;
+	struct rxrpc_key_token *token;
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxgk_response rhdr;
+	struct rxgk_context *gk;
+	struct key *key = NULL;
+	unsigned int offset = sizeof(struct rxrpc_wire_header);
+	unsigned int len = skb->len - sizeof(struct rxrpc_wire_header);
+	unsigned int token_offset, token_len;
+	unsigned int auth_offset, auth_len;
+	__be32 xauth_len;
+	int ret, ec;
+
+	_enter("{%d}", conn->debug_id);
+
+	/* Parse the RXGK_Response object */
+	if (sizeof(rhdr) + sizeof(__be32) > len)
+		goto short_packet;
+
+	if (skb_copy_bits(skb, offset, &rhdr, sizeof(rhdr)) < 0)
+		goto short_packet;
+	offset	+= sizeof(rhdr);
+	len	-= sizeof(rhdr);
+
+	token_offset	= offset;
+	token_len	= ntohl(rhdr.token_len);
+	if (xdr_round_up(token_len) + sizeof(__be32) > len)
+		goto short_packet;
+
+	offset	+= xdr_round_up(token_len);
+	len	-= xdr_round_up(token_len);
+
+	if (skb_copy_bits(skb, offset, &xauth_len, sizeof(xauth_len)) < 0)
+		goto short_packet;
+	offset	+= sizeof(xauth_len);
+	len	-= sizeof(xauth_len);
+
+	auth_offset	= offset;
+	auth_len	= ntohl(xauth_len);
+	if (auth_len < len)
+		goto short_packet;
+	if (auth_len & 3)
+		goto inconsistent;
+	if (auth_len < 20 + 9 * 4)
+		goto auth_too_short;
+
+	/* We need to extract and decrypt the token and instantiate a session
+	 * key for it.  This bit, however, is application-specific.  If
+	 * possible, we use a default parser, but we might end up bumping this
+	 * to the app to deal with - which might mean a round trip to
+	 * userspace.
+	 */
+	ret = rxgk_extract_token(conn, skb, token_offset, token_len, &key);
+	if (ret < 0)
+		goto out;
+
+	/* We now have a key instantiated from the decrypted ticket.  We can
+	 * pass this to the application so that they can parse the ticket
+	 * content and we can use the session key it contains to derive the
+	 * keys we need.
+	 *
+	 * Note that we have to switch enctype at this point as the enctype of
+	 * the ticket doesn't necessarily match that of the transport.
+	 */
+	token = key->payload.data[0];
+	conn->security_level = token->rxgk->level;
+	conn->rxgk.start_time = __be64_to_cpu(rhdr.start_time);
+
+	gk = rxgk_generate_transport_key(conn, token->rxgk, sp->hdr.cksum, GFP_NOFS);
+	if (IS_ERR(gk)) {
+		ret = PTR_ERR(gk);
+		goto cant_get_token;
+	}
+
+	krb5 = gk->krb5;
+
+	trace_rxrpc_rx_response(conn, sp->hdr.serial, krb5->etype, sp->hdr.cksum, token_len);
+
+	/* Decrypt, parse and verify the authenticator. */
+	ret = rxgk_decrypt_skb(krb5, gk->resp_enc, skb,
+			       &auth_offset, &auth_len, &ec);
+	if (ret < 0) {
+		rxrpc_abort_conn(conn, skb, RXGK_SEALEDINCON, ret,
+				 rxgk_abort_resp_auth_dec);
+		goto out;
+	}
+
+	ret = rxgk_verify_authenticator(conn, krb5, skb, auth_offset, auth_len);
+	if (ret < 0)
+		goto out;
+
+	conn->key = key;
+	key = NULL;
+	ret = 0;
+out:
+	key_put(key);
+	_leave(" = %d", ret);
+	return ret;
+
+inconsistent:
+	ret = rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+			       rxgk_abort_resp_xdr_align);
+	goto out;
+auth_too_short:
+	ret = rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+			       rxgk_abort_resp_short_auth);
+	goto out;
+short_packet:
+	ret = rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+			       rxgk_abort_resp_short_packet);
+	goto out;
+
+cant_get_token:
+	switch (ret) {
+	case -ENOMEM:
+		goto temporary_error;
+	case -EINVAL:
+		ret = rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EKEYREJECTED,
+				       rxgk_abort_resp_internal_error);
+		goto out;
+	case -ENOPKG:
+		ret = rxrpc_abort_conn(conn, skb, KRB5_PROG_KEYTYPE_NOSUPP,
+				       -EKEYREJECTED, rxgk_abort_resp_nopkg);
+		goto out;
+	}
+
+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.
+	 */
+	goto out;
+}
+
+/*
+ * clear the connection security
+ */
+static void rxgk_clear(struct rxrpc_connection *conn)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(conn->rxgk.keys); i++)
+		rxgk_put(conn->rxgk.keys[i]);
+}
+
+/*
+ * Initialise the RxGK security service.
+ */
+static int rxgk_init(void)
+{
+	return 0;
+}
+
+/*
+ * Clean up the RxGK security service.
+ */
+static void rxgk_exit(void)
+{
+}
+
+/*
+ * RxRPC YFS GSSAPI-based security
+ */
+const struct rxrpc_security rxgk_yfs = {
+	.name				= "yfs-rxgk",
+	.security_index			= RXRPC_SECURITY_YFS_RXGK,
+	.no_key_abort			= RXGK_NOTAUTH,
+	.init				= rxgk_init,
+	.exit				= rxgk_exit,
+	.preparse_server_key		= rxgk_preparse_server_key,
+	.free_preparse_server_key	= rxgk_free_preparse_server_key,
+	.destroy_server_key		= rxgk_destroy_server_key,
+	.describe_server_key		= rxgk_describe_server_key,
+	.init_connection_security	= rxgk_init_connection_security,
+	.alloc_txbuf			= rxgk_alloc_txbuf,
+	.secure_packet			= rxgk_secure_packet,
+	.verify_packet			= rxgk_verify_packet,
+	.free_call_crypto		= rxgk_free_call_crypto,
+	.issue_challenge		= rxgk_issue_challenge,
+	.validate_challenge		= rxgk_validate_challenge,
+	.challenge_to_recvmsg		= rxgk_challenge_to_recvmsg,
+	.sendmsg_respond_to_challenge	= rxgk_sendmsg_respond_to_challenge,
+	.respond_to_challenge		= rxgk_respond_to_challenge_no_appdata,
+	.verify_response		= rxgk_verify_response,
+	.clear				= rxgk_clear,
+	.default_decode_ticket		= rxgk_yfs_decode_ticket,
+};
diff --git a/net/rxrpc/rxgk_app.c b/net/rxrpc/rxgk_app.c
new file mode 100644
index 000000000000..6206a84395b8
--- /dev/null
+++ b/net/rxrpc/rxgk_app.c
@@ -0,0 +1,285 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Application-specific bits for GSSAPI-based RxRPC security
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/key-type.h>
+#include "ar-internal.h"
+#include "rxgk_common.h"
+
+/*
+ * Decode a default-style YFS ticket in a response and turn it into an
+ * rxrpc-type key.
+ *
+ * struct rxgk_key {
+ *	afs_uint32	enctype;
+ *	opaque		key<>;
+ * };
+ *
+ * struct RXGK_AuthName {
+ *	afs_int32	kind;
+ *	opaque		data<AUTHDATAMAX>;
+ *	opaque		display<AUTHPRINTABLEMAX>;
+ * };
+ *
+ * struct RXGK_Token {
+ *	rxgk_key		K0;
+ *	RXGK_Level		level;
+ *	rxgkTime		starttime;
+ *	afs_int32		lifetime;
+ *	afs_int32		bytelife;
+ *	rxgkTime		expirationtime;
+ *	struct RXGK_AuthName	identities<>;
+ * };
+ */
+int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
+			   unsigned int ticket_offset, unsigned int ticket_len,
+			   struct key **_key)
+{
+	struct rxrpc_key_token *token;
+	const struct cred *cred = current_cred(); // TODO - use socket creds
+	struct key *key;
+	size_t pre_ticket_len, payload_len;
+	unsigned int klen, enctype;
+	void *payload, *ticket;
+	__be32 *t, *p, *q, tmp[2];
+	int ret;
+
+	_enter("");
+
+	/* Get the session key length */
+	ret = skb_copy_bits(skb, ticket_offset, tmp, sizeof(tmp));
+	if (ret < 0)
+		return rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+					rxgk_abort_resp_short_yfs_klen);
+	enctype = ntohl(tmp[0]);
+	klen = ntohl(tmp[1]);
+
+	if (klen > ticket_len - 10 * sizeof(__be32))
+		return rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+					rxgk_abort_resp_short_yfs_key);
+
+	pre_ticket_len = ((5 + 14) * sizeof(__be32) +
+			  xdr_round_up(klen) +
+			  sizeof(__be32));
+	payload_len = pre_ticket_len + xdr_round_up(ticket_len);
+
+	payload = kzalloc(payload_len, GFP_NOFS);
+	if (!payload)
+		return -ENOMEM;
+
+	/* We need to fill out the XDR form for a key payload that we can pass
+	 * to add_key().  Start by copying in the ticket so that we can parse
+	 * it.
+	 */
+	ticket = payload + pre_ticket_len;
+	ret = skb_copy_bits(skb, ticket_offset, ticket, ticket_len);
+	if (ret < 0) {
+		ret = rxrpc_abort_conn(conn, skb, RXGK_INCONSISTENCY, -EPROTO,
+				       rxgk_abort_resp_short_yfs_tkt);
+		goto error;
+	}
+
+	/* Fill out the form header. */
+	p = payload;
+	p[0] = htonl(0); /* Flags */
+	p[1] = htonl(1); /* len(cellname) */
+	p[2] = htonl(0x20000000); /* Cellname " " */
+	p[3] = htonl(1); /* #tokens */
+	p[4] = htonl(15 * sizeof(__be32) + xdr_round_up(klen) +
+		     xdr_round_up(ticket_len)); /* Token len */
+
+	/* Now fill in the body.  Most of this we can just scrape directly from
+	 * the ticket.
+	 */
+	t = ticket + sizeof(__be32) * 2 + xdr_round_up(klen);
+	q = payload + 5 * sizeof(__be32);
+	q[0]  = htonl(RXRPC_SECURITY_YFS_RXGK);
+	q[1]  = t[1];		/* begintime - msw */
+	q[2]  = t[2];		/* - lsw */
+	q[3]  = t[5];		/* endtime - msw */
+	q[4]  = t[6];		/* - lsw */
+	q[5]  = 0;		/* level - msw */
+	q[6]  = t[0];		/* - lsw */
+	q[7]  = 0;		/* lifetime - msw */
+	q[8]  = t[3];		/* - lsw */
+	q[9]  = 0;		/* bytelife - msw */
+	q[10] = t[4];		/* - lsw */
+	q[11] = 0;		/* enctype - msw */
+	q[12] = htonl(enctype);	/* - lsw */
+	q[13] = htonl(klen);	/* Key length */
+
+	q += 14;
+
+	memcpy(q, ticket + sizeof(__be32) * 2, klen);
+	q += xdr_round_up(klen) / 4;
+	q[0] = htonl(ticket_len);
+	q++;
+	if (WARN_ON((unsigned long)q != (unsigned long)ticket)) {
+		ret = -EIO;
+		goto error;
+	}
+
+	/* Ticket read in with skb_copy_bits above */
+	q += xdr_round_up(ticket_len) / 4;
+	if (WARN_ON((unsigned long)q - (unsigned long)payload != payload_len)) {
+		ret = -EIO;
+		goto error;
+	}
+
+	/* Now turn that into a key. */
+	key = key_alloc(&key_type_rxrpc, "x",
+			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, // TODO: Use socket owner
+			KEY_USR_VIEW,
+			KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(key)) {
+		_leave(" = -ENOMEM [alloc %ld]", PTR_ERR(key));
+		goto error;
+	}
+
+	_debug("key %d", key_serial(key));
+
+	ret = key_instantiate_and_link(key, payload, payload_len, NULL, NULL);
+	if (ret < 0)
+		goto error_key;
+
+	token = key->payload.data[0];
+	token->no_leak_key = true;
+	*_key = key;
+	key = NULL;
+	ret = 0;
+	goto error;
+
+error_key:
+	key_put(key);
+error:
+	kfree_sensitive(payload);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Extract the token and set up a session key from the details.
+ *
+ * struct RXGK_TokenContainer {
+ *	afs_int32	kvno;
+ *	afs_int32	enctype;
+ *	opaque		encrypted_token<>;
+ * };
+ *
+ * [tools.ietf.org/html/draft-wilkinson-afs3-rxgk-afs-08 sec 6.1]
+ */
+int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
+		       unsigned int token_offset, unsigned int token_len,
+		       struct key **_key)
+{
+	const struct krb5_enctype *krb5;
+	const struct krb5_buffer *server_secret;
+	struct crypto_aead *token_enc = NULL;
+	struct key *server_key;
+	unsigned int ticket_offset, ticket_len;
+	u32 kvno, enctype;
+	int ret, ec;
+
+	struct {
+		__be32 kvno;
+		__be32 enctype;
+		__be32 token_len;
+	} container;
+
+	/* Decode the RXGK_TokenContainer object.  This tells us which server
+	 * key we should be using.  We can then fetch the key, get the secret
+	 * and set up the crypto to extract the token.
+	 */
+	if (skb_copy_bits(skb, token_offset, &container, sizeof(container)) < 0)
+		return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+					rxgk_abort_resp_tok_short);
+
+	kvno		= ntohl(container.kvno);
+	enctype		= ntohl(container.enctype);
+	ticket_len	= ntohl(container.token_len);
+	ticket_offset	= token_offset + sizeof(container);
+
+	if (xdr_round_up(ticket_len) > token_len - 3 * 4)
+		return rxrpc_abort_conn(conn, skb, RXGK_PACKETSHORT, -EPROTO,
+					rxgk_abort_resp_tok_short);
+
+	_debug("KVNO %u", kvno);
+	_debug("ENC  %u", enctype);
+	_debug("TLEN %u", ticket_len);
+
+	server_key = rxrpc_look_up_server_security(conn, skb, kvno, enctype);
+	if (IS_ERR(server_key))
+		goto cant_get_server_key;
+
+	down_read(&server_key->sem);
+	server_secret = (const void *)&server_key->payload.data[2];
+	ret = rxgk_set_up_token_cipher(server_secret, &token_enc, enctype, &krb5, GFP_NOFS);
+	up_read(&server_key->sem);
+	key_put(server_key);
+	if (ret < 0)
+		goto cant_get_token;
+
+	/* We can now decrypt and parse the token/ticket.  This allows us to
+	 * gain access to K0, from which we can derive the transport key and
+	 * thence decode the authenticator.
+	 */
+	ret = rxgk_decrypt_skb(krb5, token_enc, skb,
+			       &ticket_offset, &ticket_len, &ec);
+	crypto_free_aead(token_enc);
+	token_enc = NULL;
+	if (ret < 0)
+		return rxrpc_abort_conn(conn, skb, ec, ret,
+					rxgk_abort_resp_tok_dec);
+
+	ret = conn->security->default_decode_ticket(conn, skb, ticket_offset,
+						    ticket_len, _key);
+	if (ret < 0)
+		goto cant_get_token;
+
+	_leave(" = 0");
+	return ret;
+
+cant_get_server_key:
+	ret = PTR_ERR(server_key);
+	switch (ret) {
+	case -ENOMEM:
+		goto temporary_error;
+	case -ENOKEY:
+	case -EKEYREJECTED:
+	case -EKEYEXPIRED:
+	case -EKEYREVOKED:
+	case -EPERM:
+		return rxrpc_abort_conn(conn, skb, RXGK_BADKEYNO, -EKEYREJECTED,
+					rxgk_abort_resp_tok_nokey);
+	default:
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EKEYREJECTED,
+					rxgk_abort_resp_tok_keyerr);
+	}
+
+cant_get_token:
+	switch (ret) {
+	case -ENOMEM:
+		goto temporary_error;
+	case -EINVAL:
+		return rxrpc_abort_conn(conn, skb, RXGK_NOTAUTH, -EKEYREJECTED,
+					rxgk_abort_resp_tok_internal_error);
+	case -ENOPKG:
+		return rxrpc_abort_conn(conn, skb, KRB5_PROG_KEYTYPE_NOSUPP,
+					-EKEYREJECTED, rxgk_abort_resp_tok_nopkg);
+	}
+
+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.
+	 */
+	return ret;
+}
diff --git a/net/rxrpc/rxgk_common.h b/net/rxrpc/rxgk_common.h
index da1464e65766..7370a5655985 100644
--- a/net/rxrpc/rxgk_common.h
+++ b/net/rxrpc/rxgk_common.h
@@ -33,6 +33,19 @@ struct rxgk_context {
 	struct crypto_aead	*resp_enc;	/* Response packet enc key */
 };
 
+#define xdr_round_up(x) (round_up((x), sizeof(__be32)))
+#define xdr_object_len(x) (4 + xdr_round_up(x))
+
+/*
+ * rxgk_app.c
+ */
+int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
+			   unsigned int ticket_offset, unsigned int ticket_len,
+			   struct key **_key);
+int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
+		       unsigned int token_offset, unsigned int token_len,
+		       struct key **_key);
+
 /*
  * rxgk_kdf.c
  */
@@ -46,3 +59,81 @@ int rxgk_set_up_token_cipher(const struct krb5_buffer *server_key,
 			     unsigned int enctype,
 			     const struct krb5_enctype **_krb5,
 			     gfp_t gfp);
+
+/*
+ * Apply decryption and checksumming functions to part of an skbuff.  The
+ * offset and length are updated to reflect the actual content of the encrypted
+ * region.
+ */
+static inline
+int rxgk_decrypt_skb(const struct krb5_enctype *krb5,
+		     struct crypto_aead *aead,
+		     struct sk_buff *skb,
+		     unsigned int *_offset, unsigned int *_len,
+		     int *_error_code)
+{
+	struct scatterlist sg[16];
+	size_t offset = 0, len = *_len;
+	int nr_sg, ret;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	nr_sg = skb_to_sgvec(skb, sg, *_offset, len);
+	if (unlikely(nr_sg < 0))
+		return nr_sg;
+
+	ret = crypto_krb5_decrypt(krb5, aead, sg, nr_sg,
+				  &offset, &len);
+	switch (ret) {
+	case 0:
+		*_offset += offset;
+		*_len = len;
+		break;
+	case -EPROTO:
+	case -EBADMSG:
+		*_error_code = RXGK_SEALEDINCON;
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+/*
+ * Check the MIC on a region of an skbuff.  The offset and length are updated
+ * to reflect the actual content of the secure region.
+ */
+static inline
+int rxgk_verify_mic_skb(const struct krb5_enctype *krb5,
+			struct crypto_shash *shash,
+			const struct krb5_buffer *metadata,
+			struct sk_buff *skb,
+			unsigned int *_offset, unsigned int *_len,
+			u32 *_error_code)
+{
+	struct scatterlist sg[16];
+	size_t offset = 0, len = *_len;
+	int nr_sg, ret;
+
+	sg_init_table(sg, ARRAY_SIZE(sg));
+	nr_sg = skb_to_sgvec(skb, sg, *_offset, len);
+	if (unlikely(nr_sg < 0))
+		return nr_sg;
+
+	ret = crypto_krb5_verify_mic(krb5, shash, metadata, sg, nr_sg,
+				     &offset, &len);
+	switch (ret) {
+	case 0:
+		*_offset += offset;
+		*_len = len;
+		break;
+	case -EPROTO:
+	case -EBADMSG:
+		*_error_code = RXGK_SEALEDINCON;
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index 8ddccee69009..0b5e007c7de9 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -177,8 +177,10 @@ static struct rxrpc_txbuf *rxkad_alloc_txbuf(struct rxrpc_call *call, size_t rem
 	if (!txb)
 		return NULL;
 
-	txb->offset += shdr;
-	txb->space = part;
+	txb->crypto_header	= 0;
+	txb->sec_header		= shdr;
+	txb->offset		+= shdr;
+	txb->space		= part;
 	return txb;
 }
 
diff --git a/net/rxrpc/security.c b/net/rxrpc/security.c
index 9784adc8f275..078d91a6b77f 100644
--- a/net/rxrpc/security.c
+++ b/net/rxrpc/security.c
@@ -20,6 +20,9 @@ static const struct rxrpc_security *rxrpc_security_types[] = {
 #ifdef CONFIG_RXKAD
 	[RXRPC_SECURITY_RXKAD]	= &rxkad,
 #endif
+#ifdef CONFIG_RXGK
+	[RXRPC_SECURITY_YFS_RXGK] = &rxgk_yfs,
+#endif
 };
 
 int __init rxrpc_init_security(void)

[PATCH net-next v2 08/13] rxrpc: rxgk: Implement connection rekeying

[David Howells]

Implement rekeying of connections with the RxGK security class.  This
involves regenerating the keys with a different key number as part of the
input data after a certain amount of time or a certain amount of bytes
encrypted.  Rekeying may be triggered by either end.

The LSW of the key number is inserted into the security-specific field in
the RX header, and we try and expand it to 32-bits to make it last longer.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
 include/trace/events/rxrpc.h |  24 ++++++
 net/rxrpc/ar-internal.h      |   5 +-
 net/rxrpc/conn_object.c      |   1 +
 net/rxrpc/rxgk.c             | 158 +++++++++++++++++++++++++++++++++--
 4 files changed, 181 insertions(+), 7 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index aab81e8196ae..920439df1f6f 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -2725,6 +2725,30 @@ TRACE_EVENT(rxrpc_rack_timer,
 		      ktime_to_us(__entry->delay))
 	    );
 
+TRACE_EVENT(rxrpc_rxgk_rekey,
+	    TP_PROTO(struct rxrpc_connection *conn,
+		     unsigned int current_key, unsigned int requested_key),
+
+	    TP_ARGS(conn, current_key, requested_key),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,	conn)
+		    __field(unsigned int,	current_key)
+		    __field(unsigned int,	requested_key)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->conn		= conn->debug_id;
+		    __entry->current_key	= current_key;
+		    __entry->requested_key	= requested_key;
+			   ),
+
+	    TP_printk("C=%08x cur=%x req=%x",
+		      __entry->conn,
+		      __entry->current_key,
+		      __entry->requested_key)
+	    );
+
 #undef EM
 #undef E_
 
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index c8d66a02c8fe..d23ea4710cb2 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -565,13 +565,16 @@ struct rxrpc_connection {
 			u32	nonce;		/* response re-use preventer */
 		} rxkad;
 		struct {
-			struct rxgk_context *keys[1];
+			struct rxgk_context *keys[4]; /* (Re-)keying buffer */
 			u64	start_time;	/* The start time for TK derivation */
 			u8	nonce[20];	/* Response re-use preventer */
 			u32	enctype;	/* Kerberos 5 encoding type */
+			u32	key_number;	/* Current key number */
 		} rxgk;
 	};
+	rwlock_t		security_use_lock; /* Security use/modification lock */
 	struct sk_buff		*tx_response;	/* Response packet to be transmitted */
+
 	unsigned long		flags;
 	unsigned long		events;
 	unsigned long		idle_timestamp;	/* Time at which last became idle */
diff --git a/net/rxrpc/conn_object.c b/net/rxrpc/conn_object.c
index f1e36cba9f4c..6733a7692443 100644
--- a/net/rxrpc/conn_object.c
+++ b/net/rxrpc/conn_object.c
@@ -73,6 +73,7 @@ struct rxrpc_connection *rxrpc_alloc_connection(struct rxrpc_net *rxnet,
 		skb_queue_head_init(&conn->rx_queue);
 		conn->rxnet = rxnet;
 		conn->security = &rxrpc_no_security;
+		rwlock_init(&conn->security_use_lock);
 		spin_lock_init(&conn->state_lock);
 		conn->debug_id = atomic_inc_return(&rxrpc_debug_id);
 		conn->idle_timestamp = jiffies;
diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
index 02752eeb2395..8b1ccdf8bc58 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -76,11 +76,155 @@ static void rxgk_describe_server_key(const struct key *key, struct seq_file *m)
 		seq_printf(m, ": %s", krb5->name);
 }
 
+/*
+ * Handle rekeying the connection when we see our limits overrun or when the
+ * far side decided to rekey.
+ *
+ * Returns a ref on the context if successful or -ESTALE if the key is out of
+ * date.
+ */
+static struct rxgk_context *rxgk_rekey(struct rxrpc_connection *conn,
+				       const u16 *specific_key_number)
+{
+	struct rxgk_context *gk, *dead = NULL;
+	unsigned int key_number, current_key, mask = ARRAY_SIZE(conn->rxgk.keys) - 1;
+	bool crank = false;
+
+	_enter("%d", specific_key_number ? *specific_key_number : -1);
+
+	mutex_lock(&conn->security_lock);
+
+	current_key = conn->rxgk.key_number;
+	if (!specific_key_number) {
+		key_number = current_key;
+	} else {
+		if (*specific_key_number == (u16)current_key)
+			key_number = current_key;
+		else if (*specific_key_number == (u16)(current_key - 1))
+			key_number = current_key - 1;
+		else if (*specific_key_number == (u16)(current_key + 1))
+			goto crank_window;
+		else
+			goto bad_key;
+	}
+
+	gk = conn->rxgk.keys[key_number & mask];
+	if (!gk)
+		goto generate_key;
+	if (!specific_key_number &&
+	    test_bit(RXGK_TK_NEEDS_REKEY, &gk->flags))
+		goto crank_window;
+
+grab:
+	refcount_inc(&gk->usage);
+	mutex_unlock(&conn->security_lock);
+	rxgk_put(dead);
+	return gk;
+
+crank_window:
+	trace_rxrpc_rxgk_rekey(conn, current_key,
+			       specific_key_number ? *specific_key_number : -1);
+	if (current_key == UINT_MAX)
+		goto bad_key;
+	if (current_key + 1 == UINT_MAX)
+		set_bit(RXRPC_CONN_DONT_REUSE, &conn->flags);
+
+	key_number = current_key + 1;
+	if (WARN_ON(conn->rxgk.keys[key_number & mask]))
+		goto bad_key;
+	crank = true;
+
+generate_key:
+	gk = conn->rxgk.keys[current_key & mask];
+	gk = rxgk_generate_transport_key(conn, gk->key, key_number, GFP_NOFS);
+	if (IS_ERR(gk)) {
+		mutex_unlock(&conn->security_lock);
+		return gk;
+	}
+
+	write_lock(&conn->security_use_lock);
+	if (crank) {
+		current_key++;
+		conn->rxgk.key_number = current_key;
+		dead = conn->rxgk.keys[(current_key - 2) & mask];
+		conn->rxgk.keys[(current_key - 2) & mask] = NULL;
+	}
+	conn->rxgk.keys[current_key & mask] = gk;
+	write_unlock(&conn->security_use_lock);
+	goto grab;
+
+bad_key:
+	mutex_unlock(&conn->security_lock);
+	return ERR_PTR(-ESTALE);
+}
+
+/*
+ * Get the specified keying context.
+ *
+ * Returns a ref on the context if successful or -ESTALE if the key is out of
+ * date.
+ */
 static struct rxgk_context *rxgk_get_key(struct rxrpc_connection *conn,
-					 u16 *specific_key_number)
+					 const u16 *specific_key_number)
 {
-	refcount_inc(&conn->rxgk.keys[0]->usage);
-	return conn->rxgk.keys[0];
+	struct rxgk_context *gk;
+	unsigned int key_number, current_key, mask = ARRAY_SIZE(conn->rxgk.keys) - 1;
+
+	_enter("{%u},%d",
+	       conn->rxgk.key_number, specific_key_number ? *specific_key_number : -1);
+
+	read_lock(&conn->security_use_lock);
+
+	current_key = conn->rxgk.key_number;
+	if (!specific_key_number) {
+		key_number = current_key;
+	} else {
+		/* Only the bottom 16 bits of the key number are exposed in the
+		 * header, so we try and keep the upper 16 bits in step.  The
+		 * whole 32 bits are used to generate the TK.
+		 */
+		if (*specific_key_number == (u16)current_key)
+			key_number = current_key;
+		else if (*specific_key_number == (u16)(current_key - 1))
+			key_number = current_key - 1;
+		else if (*specific_key_number == (u16)(current_key + 1))
+			goto rekey;
+		else
+			goto bad_key;
+	}
+
+	gk = conn->rxgk.keys[key_number & mask];
+	if (!gk)
+		goto slow_path;
+	if (!specific_key_number &&
+	    key_number < UINT_MAX) {
+		if (time_after(jiffies, gk->expiry) ||
+		    gk->bytes_remaining < 0) {
+			set_bit(RXGK_TK_NEEDS_REKEY, &gk->flags);
+			goto slow_path;
+		}
+
+		if (test_bit(RXGK_TK_NEEDS_REKEY, &gk->flags))
+			goto slow_path;
+	}
+
+	refcount_inc(&gk->usage);
+	read_unlock(&conn->security_use_lock);
+	return gk;
+
+rekey:
+	_debug("rekey");
+	if (current_key == UINT_MAX)
+		goto bad_key;
+	gk = conn->rxgk.keys[current_key & mask];
+	if (gk)
+		set_bit(RXGK_TK_NEEDS_REKEY, &gk->flags);
+slow_path:
+	read_unlock(&conn->security_use_lock);
+	return rxgk_rekey(conn, specific_key_number);
+bad_key:
+	read_unlock(&conn->security_use_lock);
+	return ERR_PTR(-ESTALE);
 }
 
 /*
@@ -92,7 +236,8 @@ static int rxgk_init_connection_security(struct rxrpc_connection *conn,
 	struct rxgk_context *gk;
 	int ret;
 
-	_enter("{%d},{%x}", conn->debug_id, key_serial(conn->key));
+	_enter("{%d,%u},{%x}",
+	       conn->debug_id, conn->rxgk.key_number, key_serial(conn->key));
 
 	conn->security_ix = token->security_index;
 	conn->security_level = token->rxgk->level;
@@ -102,11 +247,12 @@ static int rxgk_init_connection_security(struct rxrpc_connection *conn,
 		do_div(conn->rxgk.start_time, 100);
 	}
 
-	gk = rxgk_generate_transport_key(conn, token->rxgk, 0, GFP_NOFS);
+	gk = rxgk_generate_transport_key(conn, token->rxgk, conn->rxgk.key_number,
+					 GFP_NOFS);
 	if (IS_ERR(gk))
 		return PTR_ERR(gk);
 	conn->rxgk.enctype = gk->krb5->etype;
-	conn->rxgk.keys[0] = gk;
+	conn->rxgk.keys[gk->key_number & 3] = gk;
 
 	switch (conn->security_level) {
 	case RXRPC_SECURITY_PLAIN: