Merge branch 'rxrpc-better-fix-for-data-response-decrypt-vs-splice'

David Howells says:

====================
rxrpc: Better fix for DATA/RESPONSE decrypt vs splice()

Here are two patches containing better fixes for the in-place decryption of
DATA and RESPONSE packets that can corrupt pagecache spliced into UDP
packets and sent to an AF_RXRPC server [CVE-2026-43500], plus a patch to
precheck the length of rxgk-secured DATA packets.

Of the main patches, one patch fixes DATA decryption by having recvmsg
unconditionally extract the data into a flat bounce buffer and, if need be,
decrypt it there.  It doesn't seem to cause a performance problem to do
this even on unencrypted packets; for encrypted packets it makes sure the
content is correctly aligned for crypto which seems to get a small
performance gain.

Further, it means that DATA packets are no longer copied in the I/O thread,
avoiding a slowdown of the protocol engine that runs there.

The other main patch fixes RESPONSE decryption by having the connection
event handler worker copy the data to a flat buffer and, again, decrypt it
there.  This simplifies RESPONSE handling.

With these two fixes, the data content of the received sk_buff no longer
gets altered.
====================

Link: https://patch.msgid.link/20260515230516.2718212-1-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

14 files changed, 309 insertions, 305 deletions

diff --git a/Documentation/crypto/krb5.rst b/Documentation/crypto/krb5.rst
index beffa0133446..f62e07ac6811 100644
--- a/Documentation/crypto/krb5.rst
+++ b/Documentation/crypto/krb5.rst
@@ -158,13 +158,22 @@ returned.
 When a message has been received, the location and size of the data with the
 message can be determined by calling::
 
-	void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
-					   enum krb5_crypto_mode mode,
-					   size_t *_offset, size_t *_len);
+	int crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+					  enum krb5_crypto_mode mode,
+					  size_t *_offset, size_t *_len);
 
 The caller provides the offset and length of the message to the function, which
 then alters those values to indicate the region containing the data (plus any
-padding).  It is up to the caller to determine how much padding there is.
+padding).  It is up to the caller to determine how much padding there is.  The
+function returns an error if the length is too small or if the mode is
+unsupported.  An additional function::
+
+	int crypto_krb5_check_data_len(const struct krb5_enctype *krb5,
+				       enum krb5_crypto_mode mode,
+				       size_t len, size_t min_content);
+
+is provided to just do a basic check that the decrypted/verified message would
+have a sufficient minimum payload.
 
 Preparation Functions
 ---------------------
diff --git a/crypto/krb5/krb5_api.c b/crypto/krb5/krb5_api.c
index 23026d4206c8..c7ea40f900a7 100644
--- a/crypto/krb5/krb5_api.c
+++ b/crypto/krb5/krb5_api.c
@@ -134,27 +134,69 @@ EXPORT_SYMBOL(crypto_krb5_how_much_data);
  * Find the offset and size of the data in a secure message so that this
  * information can be used in the metadata buffer which will get added to the
  * digest by crypto_krb5_verify_mic().
+ *
+ * Return: 0 if successful, -EBADMSG if the message is too short or -EINVAL if
+ * the mode is unsupported.
  */
-void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
-				   enum krb5_crypto_mode mode,
-				   size_t *_offset, size_t *_len)
+int crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+				  enum krb5_crypto_mode mode,
+				  size_t *_offset, size_t *_len)
 {
 	switch (mode) {
 	case KRB5_CHECKSUM_MODE:
+		if (*_len < krb5->cksum_len)
+			return -EBADMSG;
 		*_offset += krb5->cksum_len;
 		*_len -= krb5->cksum_len;
-		return;
+		return 0;
 	case KRB5_ENCRYPT_MODE:
+		if (*_len < krb5->conf_len + krb5->cksum_len)
+			return -EBADMSG;
 		*_offset += krb5->conf_len;
 		*_len -= krb5->conf_len + krb5->cksum_len;
-		return;
+		return 0;
 	default:
 		WARN_ON_ONCE(1);
-		return;
+		return -EINVAL;
 	}
 }
 EXPORT_SYMBOL(crypto_krb5_where_is_the_data);
 
+/**
+ * crypto_krb5_check_data_len - Check a message is big enough
+ * @krb5: The encoding to use.
+ * @mode: Mode of operation.
+ * @len: The length of the secure blob.
+ * @min_content: Minimum length of the content inside the blob.
+ *
+ * Check that a message is large enough to hold whatever bits the encryption
+ * type wants to glue on (nonce, checksum) plus a minimum amount of content.
+ *
+ * Return: 0 if successful, -EBADMSG if the message is too short or -EINVAL if
+ * the mode is unsupported.
+ */
+int crypto_krb5_check_data_len(const struct krb5_enctype *krb5,
+			       enum krb5_crypto_mode mode,
+			       size_t len, size_t min_content)
+{
+	switch (mode) {
+	case KRB5_CHECKSUM_MODE:
+		if (len < krb5->cksum_len ||
+		    len - krb5->cksum_len < min_content)
+			return -EBADMSG;
+		return 0;
+	case KRB5_ENCRYPT_MODE:
+		if (len < krb5->conf_len + krb5->cksum_len ||
+		    len - (krb5->conf_len + krb5->cksum_len) < min_content)
+			return -EBADMSG;
+		return 0;
+	default:
+		WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+}
+EXPORT_SYMBOL(crypto_krb5_check_data_len);
+
 /*
  * Prepare the encryption with derived key data.
  */
diff --git a/include/crypto/krb5.h b/include/crypto/krb5.h
index 71dd38f59be1..aac3ecf88467 100644
--- a/include/crypto/krb5.h
+++ b/include/crypto/krb5.h
@@ -121,9 +121,12 @@ size_t crypto_krb5_how_much_buffer(const struct krb5_enctype *krb5,
 size_t crypto_krb5_how_much_data(const struct krb5_enctype *krb5,
 				 enum krb5_crypto_mode mode,
 				 size_t *_buffer_size, size_t *_offset);
-void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
-				   enum krb5_crypto_mode mode,
-				   size_t *_offset, size_t *_len);
+int crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+				  enum krb5_crypto_mode mode,
+				  size_t *_offset, size_t *_len);
+int crypto_krb5_check_data_len(const struct krb5_enctype *krb5,
+			       enum krb5_crypto_mode mode,
+			       size_t len, size_t min_content);
 struct crypto_aead *crypto_krb5_prepare_encryption(const struct krb5_enctype *krb5,
 						   const struct krb5_buffer *TK,
 						   u32 usage, gfp_t gfp);
diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 573f2df3a2c9..704a10de6670 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -71,6 +71,7 @@
 	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_short_header,		"rxgk1-short-hdr")	\
 	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")	\
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 27c2aa2dd023..98f2165159d7 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -213,8 +213,6 @@ struct rxrpc_skb_priv {
 		struct {
 			u16		offset;		/* Offset of data */
 			u16		len;		/* Length of data */
-			u8		flags;
-#define RXRPC_RX_VERIFIED	0x01
 		};
 		struct {
 			rxrpc_seq_t	first_ack;	/* First packet in acks table */
@@ -309,15 +307,16 @@ struct rxrpc_security {
 				    struct sk_buff *challenge);
 
 	/* verify a response */
-	int (*verify_response)(struct rxrpc_connection *,
-			       struct sk_buff *);
+	int (*verify_response)(struct rxrpc_connection *conn,
+			       struct sk_buff *response_skb,
+			       void *response, unsigned int len);
 
 	/* 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,
+				     void *ticket, unsigned int ticket_len,
 				     struct key **_key);
 };
 
@@ -774,6 +773,11 @@ struct rxrpc_call {
 	struct sk_buff_head	recvmsg_queue;	/* Queue of packets ready for recvmsg() */
 	struct sk_buff_head	rx_queue;	/* Queue of packets for this call to receive */
 	struct sk_buff_head	rx_oos_queue;	/* Queue of out of sequence packets */
+	void			*rx_dec_buffer;	/* Decryption buffer */
+	unsigned short		rx_dec_bsize;	/* rx_dec_buffer size */
+	unsigned short		rx_dec_offset;	/* Decrypted packet data offset */
+	unsigned short		rx_dec_len;	/* Decrypted packet data len */
+	rxrpc_seq_t		rx_dec_seq;	/* Packet in decryption buffer */
 
 	rxrpc_seq_t		rx_highest_seq;	/* Higest sequence number received */
 	rxrpc_seq_t		rx_consumed;	/* Highest packet consumed */
diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 2b19b252225e..fec59d9338b9 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -332,27 +332,7 @@ bool rxrpc_input_call_event(struct rxrpc_call *call)
 
 			saw_ack |= sp->hdr.type == RXRPC_PACKET_TYPE_ACK;
 
-			if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA &&
-			    sp->hdr.securityIndex != 0 &&
-			    (skb_cloned(skb) ||
-			     skb_has_frag_list(skb) ||
-			     skb_has_shared_frag(skb))) {
-				/* Unshare the packet so that it can be
-				 * modified by in-place decryption.
-				 */
-				struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
-
-				if (nskb) {
-					rxrpc_new_skb(nskb, rxrpc_skb_new_unshared);
-					rxrpc_input_call_packet(call, nskb);
-					rxrpc_free_skb(nskb, rxrpc_skb_put_call_rx);
-				} else {
-					/* OOM - Drop the packet. */
-					rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
-				}
-			} else {
-				rxrpc_input_call_packet(call, skb);
-			}
+			rxrpc_input_call_packet(call, skb);
 			rxrpc_free_skb(skb, rxrpc_skb_put_call_rx);
 			did_receive = true;
 		}
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index f035f486c139..fcb9d38bb521 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -152,6 +152,7 @@ struct rxrpc_call *rxrpc_alloc_call(struct rxrpc_sock *rx, gfp_t gfp,
 	spin_lock_init(&call->notify_lock);
 	refcount_set(&call->ref, 1);
 	call->debug_id		= debug_id;
+	call->rx_pkt_offset	= USHRT_MAX;
 	call->tx_total_len	= -1;
 	call->tx_jumbo_max	= 1;
 	call->next_rx_timo	= 20 * HZ;
@@ -553,6 +554,7 @@ static void rxrpc_cleanup_rx_buffers(struct rxrpc_call *call)
 	rxrpc_purge_queue(&call->recvmsg_queue);
 	rxrpc_purge_queue(&call->rx_queue);
 	rxrpc_purge_queue(&call->rx_oos_queue);
+	kfree(call->rx_dec_buffer);
 }
 
 /*
diff --git a/net/rxrpc/conn_event.c b/net/rxrpc/conn_event.c
index 442414d90ba1..c96ca615b787 100644
--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -243,28 +243,22 @@ static void rxrpc_call_is_secure(struct rxrpc_call *call)
 static int rxrpc_verify_response(struct rxrpc_connection *conn,
 				 struct sk_buff *skb)
 {
+	unsigned int len = skb->len - sizeof(struct rxrpc_wire_header);
+	void *buffer;
 	int ret;
 
-	if (skb_cloned(skb) || skb_has_frag_list(skb) ||
-	    skb_has_shared_frag(skb)) {
-		/* Copy the packet if shared so that we can do in-place
-		 * decryption.
-		 */
-		struct sk_buff *nskb = skb_copy(skb, GFP_NOFS);
-
-		if (nskb) {
-			rxrpc_new_skb(nskb, rxrpc_skb_new_unshared);
-			ret = conn->security->verify_response(conn, nskb);
-			rxrpc_free_skb(nskb, rxrpc_skb_put_response_copy);
-		} else {
-			/* OOM - Drop the packet. */
-			rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
-			ret = -ENOMEM;
-		}
-	} else {
-		ret = conn->security->verify_response(conn, skb);
-	}
+	buffer = kmalloc(len, GFP_NOFS);
+	if (!buffer)
+		return -ENOMEM;
+
+	ret = skb_copy_bits(skb, sizeof(struct rxrpc_wire_header), buffer, len);
+	if (ret < 0)
+		goto out;
+
+	ret = conn->security->verify_response(conn, skb, buffer, len);
 
+out:
+	kfree(buffer);
 	return ret;
 }
 
diff --git a/net/rxrpc/insecure.c b/net/rxrpc/insecure.c
index 0a260df45d25..0b39046bdc61 100644
--- a/net/rxrpc/insecure.c
+++ b/net/rxrpc/insecure.c
@@ -32,9 +32,6 @@ static int none_secure_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
 
 static int none_verify_packet(struct rxrpc_call *call, struct sk_buff *skb)
 {
-	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
-
-	sp->flags |= RXRPC_RX_VERIFIED;
 	return 0;
 }
 
@@ -57,9 +54,10 @@ static int none_sendmsg_respond_to_challenge(struct sk_buff *challenge,
 }
 
 static int none_verify_response(struct rxrpc_connection *conn,
-				struct sk_buff *skb)
+				struct sk_buff *response_skb,
+				void *response, unsigned int len)
 {
-	return rxrpc_abort_conn(conn, skb, RX_PROTOCOL_ERROR, -EPROTO,
+	return rxrpc_abort_conn(conn, response_skb, RX_PROTOCOL_ERROR, -EPROTO,
 				rxrpc_eproto_rxnull_response);
 }
 
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index e1f7513a46db..c940600117a4 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -147,15 +147,52 @@ static void rxrpc_rotate_rx_window(struct rxrpc_call *call)
 }
 
 /*
- * Decrypt and verify a DATA packet.
+ * Decrypt and verify a DATA packet.  The content of the packet is pulled out
+ * into a flat buffer rather than decrypting in place in the skbuff.  This also
+ * has the advantage of aligning the buffer correctly for the crypto routines.
+ *
+ * We keep track of the sequence number of the packet currently decrypted into
+ * the buffer in ->rx_dec_seq.  If MSG_PEEK is used and steps onto a new
+ * packet, subsequent recvmsg() calls will have to go back and re-decrypt the
+ * current packet.
  */
 static int rxrpc_verify_data(struct rxrpc_call *call, struct sk_buff *skb)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	int ret;
 
-	if (sp->flags & RXRPC_RX_VERIFIED)
-		return 0;
-	return call->security->verify_packet(call, skb);
+	if (sp->len > call->rx_dec_bsize) {
+		/* Make sure we can hold a 1412-byte jumbo subpacket and make
+		 * sure that the buffer size is aligned to a crypto blocksize.
+		 */
+		size_t size = clamp(round_up(sp->len, 32), 2048, 65535);
+		void *buffer = krealloc(call->rx_dec_buffer, size, GFP_NOFS);
+
+		if (!buffer)
+			return -ENOMEM;
+		call->rx_dec_buffer = buffer;
+		call->rx_dec_bsize = size;
+	}
+
+	ret = -EFAULT;
+	if (skb_copy_bits(skb, sp->offset, call->rx_dec_buffer, sp->len) < 0)
+		goto err;
+
+	call->rx_dec_offset = 0;
+	call->rx_dec_len = sp->len;
+	call->rx_dec_seq = sp->hdr.seq;
+	ret = call->security->verify_packet(call, skb);
+	if (ret < 0)
+		goto err;
+	return 0;
+
+err:
+	kfree(call->rx_dec_buffer);
+	call->rx_dec_buffer = NULL;
+	call->rx_dec_bsize = 0;
+	call->rx_dec_offset = 0;
+	call->rx_dec_len = 0;
+	return ret;
 }
 
 /*
@@ -283,16 +320,21 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 		if (msg)
 			sock_recv_timestamp(msg, sock->sk, skb);
 
-		if (rx_pkt_offset == 0) {
+		if (call->rx_dec_seq != sp->hdr.seq ||
+		    !call->rx_dec_buffer) {
 			ret2 = rxrpc_verify_data(call, skb);
 			trace_rxrpc_recvdata(call, rxrpc_recvmsg_next, seq,
-					     sp->offset, sp->len, ret2);
+					     call->rx_dec_offset,
+					     call->rx_dec_len, ret2);
 			if (ret2 < 0) {
 				ret = ret2;
 				goto out;
 			}
-			rx_pkt_offset = sp->offset;
-			rx_pkt_len = sp->len;
+		}
+
+		if (rx_pkt_offset == USHRT_MAX) {
+			rx_pkt_offset = call->rx_dec_offset;
+			rx_pkt_len = call->rx_dec_len;
 		} else {
 			trace_rxrpc_recvdata(call, rxrpc_recvmsg_cont, seq,
 					     rx_pkt_offset, rx_pkt_len, 0);
@@ -304,10 +346,10 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 		if (copy > remain)
 			copy = remain;
 		if (copy > 0) {
-			ret2 = skb_copy_datagram_iter(skb, rx_pkt_offset, iter,
-						      copy);
-			if (ret2 < 0) {
-				ret = ret2;
+			ret2 = copy_to_iter(call->rx_dec_buffer + rx_pkt_offset,
+					    copy, iter);
+			if (ret2 != copy) {
+				ret = -EFAULT;
 				goto out;
 			}
 
@@ -328,7 +370,7 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 		/* The whole packet has been transferred. */
 		if (sp->hdr.flags & RXRPC_LAST_PACKET)
 			ret = 1;
-		rx_pkt_offset = 0;
+		rx_pkt_offset = USHRT_MAX;
 		rx_pkt_len = 0;
 
 		skb = skb_peek_next(skb, &call->recvmsg_queue);
diff --git a/net/rxrpc/rxgk.c b/net/rxrpc/rxgk.c
index 0d5e654da918..a1ee102abae1 100644
--- a/net/rxrpc/rxgk.c
+++ b/net/rxrpc/rxgk.c
@@ -473,15 +473,20 @@ static int rxgk_verify_packet_integrity(struct rxrpc_call *call,
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	struct rxgk_header *hdr;
 	struct krb5_buffer metadata;
-	unsigned int offset = sp->offset, len = sp->len;
+	unsigned int len = call->rx_dec_len;
 	size_t data_offset = 0, data_len = len;
+	void *data = call->rx_dec_buffer, *p = data;
 	u32 ac = 0;
 	int ret = -ENOMEM;
 
 	_enter("");
 
-	crypto_krb5_where_is_the_data(gk->krb5, KRB5_CHECKSUM_MODE,
-				      &data_offset, &data_len);
+	if (crypto_krb5_where_is_the_data(gk->krb5, KRB5_CHECKSUM_MODE,
+					  &data_offset, &data_len) < 0) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+					 rxgk_abort_1_short_header);
+		goto put_gk;
+	}
 
 	hdr = kzalloc_obj(*hdr, GFP_NOFS);
 	if (!hdr)
@@ -496,16 +501,15 @@ static int rxgk_verify_packet_integrity(struct rxrpc_call *call,
 
 	metadata.len = sizeof(*hdr);
 	metadata.data = hdr;
-	ret = rxgk_verify_mic_skb(gk->krb5, gk->rx_Kc, &metadata,
-				  skb, &offset, &len, &ac);
+	ret = rxgk_verify_mic(gk->krb5, gk->rx_Kc, &metadata, &p, &len, &ac);
 	kfree(hdr);
 	if (ret < 0) {
 		if (ret != -ENOMEM)
 			rxrpc_abort_eproto(call, skb, ac,
 					   rxgk_abort_1_verify_mic_eproto);
 	} else {
-		sp->offset = offset;
-		sp->len = len;
+		call->rx_dec_offset = p - data;
+		call->rx_dec_len = len;
 	}
 
 put_gk:
@@ -522,49 +526,53 @@ static int rxgk_verify_packet_encrypted(struct rxrpc_call *call,
 					struct sk_buff *skb)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
-	struct rxgk_header hdr;
-	unsigned int offset = sp->offset, len = sp->len;
+	struct rxgk_header *hdr;
+	unsigned int offset = 0, len = call->rx_dec_len;
+	void *data = call->rx_dec_buffer, *p = data;
 	int ret;
 	u32 ac = 0;
 
 	_enter("");
 
-	ret = rxgk_decrypt_skb(gk->krb5, gk->rx_enc, skb, &offset, &len, &ac);
+	if (crypto_krb5_check_data_len(gk->krb5, KRB5_ENCRYPT_MODE,
+				       len, sizeof(*hdr)) < 0) {
+		ret = rxrpc_abort_eproto(call, skb, RXGK_PACKETSHORT,
+					 rxgk_abort_2_short_header);
+		goto error;
+	}
+
+	ret = rxgk_decrypt(gk->krb5, gk->rx_enc, &p, &len, &ac);
 	if (ret < 0) {
 		if (ret != -ENOMEM)
 			rxrpc_abort_eproto(call, skb, ac, rxgk_abort_2_decrypt_eproto);
 		goto error;
 	}
+	offset = p - data;
 
-	if (len < sizeof(hdr)) {
+	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) {
+	hdr = data + offset;
+	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);
+	call->rx_dec_offset = offset;
+	call->rx_dec_len = ntohl(hdr->data_len);
 	ret = 0;
 error:
 	rxgk_put(gk);
@@ -1076,11 +1084,12 @@ static int rxgk_sendmsg_respond_to_challenge(struct sk_buff *challenge,
  *	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)
+static int rxgk_verify_authenticator(struct rxrpc_connection *conn,
+				     const struct krb5_enctype *krb5,
+				     struct sk_buff *skb,
+				     void *auth, unsigned int auth_len)
 {
+	__be32 *p = auth, *end = auth + auth_len;
 	u32 app_len, call_count, level, epoch, cid, i;
 
 	_enter("");
@@ -1144,37 +1153,6 @@ static int rxgk_do_verify_authenticator(struct rxrpc_connection *conn,
 }
 
 /*
- * 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 / sizeof(*p));
-error:
-	kfree(auth);
-	return ret;
-}
-
-/*
  * Verify a response.
  *
  * struct RXGK_Response {
@@ -1184,49 +1162,45 @@ error:
  * };
  */
 static int rxgk_verify_response(struct rxrpc_connection *conn,
-				struct sk_buff *skb)
+				struct sk_buff *skb,
+				void *buffer, unsigned int len)
 {
 	const struct krb5_enctype *krb5;
 	struct rxrpc_key_token *token;
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
-	struct rxgk_response rhdr;
+	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;
+	unsigned int resp_token_len, auth_len;
+	void *resp_token, *auth;
 	__be32 xauth_len;
 	int ret, ec;
 
 	_enter("{%d}", conn->debug_id);
 
 	/* Parse the RXGK_Response object */
-	if (sizeof(rhdr) + sizeof(__be32) > len)
+	if (len < sizeof(*rhdr) + sizeof(__be32))
 		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 (token_len > len ||
-	    xdr_round_up(token_len) + sizeof(__be32) > len)
+	rhdr = buffer;
+	buffer	+= sizeof(*rhdr);
+	len	-= sizeof(*rhdr);
+
+	resp_token	= buffer;
+	resp_token_len	= ntohl(rhdr->token_len);
+	if (resp_token_len > len ||
+	    xdr_round_up(resp_token_len) + sizeof(__be32) > len)
 		goto short_packet;
 
-	trace_rxrpc_rx_response(conn, sp->hdr.serial, 0, sp->hdr.cksum, token_len);
+	trace_rxrpc_rx_response(conn, sp->hdr.serial, 0, sp->hdr.cksum, resp_token_len);
 
-	offset	+= xdr_round_up(token_len);
-	len	-= xdr_round_up(token_len);
+	buffer	+= xdr_round_up(resp_token_len);
+	len	-= xdr_round_up(resp_token_len);
 
-	if (skb_copy_bits(skb, offset, &xauth_len, sizeof(xauth_len)) < 0)
-		goto short_packet;
-	offset	+= sizeof(xauth_len);
+	xauth_len = *(__be32 *)buffer;
+	buffer	+= sizeof(xauth_len);
 	len	-= sizeof(xauth_len);
 
-	auth_offset	= offset;
+	auth		= buffer;
 	auth_len	= ntohl(xauth_len);
 	if (auth_len > len)
 		goto short_packet;
@@ -1241,7 +1215,7 @@ static int rxgk_verify_response(struct rxrpc_connection *conn,
 	 * 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);
+	ret = rxgk_extract_token(conn, skb, resp_token, resp_token_len, &key);
 	if (ret < 0)
 		goto out;
 
@@ -1255,7 +1229,7 @@ static int rxgk_verify_response(struct rxrpc_connection *conn,
 	 */
 	token = key->payload.data[0];
 	conn->security_level = token->rxgk->level;
-	conn->rxgk.start_time = __be64_to_cpu(rhdr.start_time);
+	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)) {
@@ -1265,18 +1239,18 @@ static int rxgk_verify_response(struct rxrpc_connection *conn,
 
 	krb5 = gk->krb5;
 
-	trace_rxrpc_rx_response(conn, sp->hdr.serial, krb5->etype, sp->hdr.cksum, token_len);
+	trace_rxrpc_rx_response(conn, sp->hdr.serial, krb5->etype, sp->hdr.cksum,
+				resp_token_len);
 
 	/* Decrypt, parse and verify the authenticator. */
-	ret = rxgk_decrypt_skb(krb5, gk->resp_enc, skb,
-			       &auth_offset, &auth_len, &ec);
+	ret = rxgk_decrypt(krb5, gk->resp_enc, &auth, &auth_len, &ec);
 	if (ret < 0) {
 		rxrpc_abort_conn(conn, skb, RXGK_SEALEDINCON, ret,
 				 rxgk_abort_resp_auth_dec);
 		goto out_gk;
 	}
 
-	ret = rxgk_verify_authenticator(conn, krb5, skb, auth_offset, auth_len);
+	ret = rxgk_verify_authenticator(conn, krb5, skb, auth, auth_len);
 	if (ret < 0)
 		goto out_gk;
 
diff --git a/net/rxrpc/rxgk_app.c b/net/rxrpc/rxgk_app.c
index 0ef2a29eb695..200a30064fae 100644
--- a/net/rxrpc/rxgk_app.c
+++ b/net/rxrpc/rxgk_app.c
@@ -40,7 +40,7 @@
  * };
  */
 int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
-			   unsigned int ticket_offset, unsigned int ticket_len,
+			   void *buffer, unsigned int ticket_len,
 			   struct key **_key)
 {
 	struct rxrpc_key_token *token;
@@ -49,7 +49,7 @@ int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
 	size_t pre_ticket_len, payload_len;
 	unsigned int klen, enctype;
 	void *payload, *ticket;
-	__be32 *t, *p, *q, tmp[2];
+	__be32 *t, *p, *q, *tmp;
 	int ret;
 
 	_enter("");
@@ -59,10 +59,7 @@ int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
 					rxgk_abort_resp_short_yfs_tkt);
 
 	/* 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);
+	tmp = buffer;
 	enctype = ntohl(tmp[0]);
 	klen = ntohl(tmp[1]);
 
@@ -84,12 +81,7 @@ int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
 	 * 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;
-	}
+	memcpy(ticket, buffer, ticket_len);
 
 	/* Fill out the form header. */
 	p = payload;
@@ -131,7 +123,7 @@ int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
 		goto error;
 	}
 
-	/* Ticket read in with skb_copy_bits above */
+	/* Ticket appended above. */
 	q += xdr_round_up(ticket_len) / 4;
 	if (WARN_ON((unsigned long)q - (unsigned long)payload != payload_len)) {
 		ret = -EIO;
@@ -182,14 +174,15 @@ error:
  * [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,
+		       void *token, 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;
+	unsigned int ticket_len;
+	void *ticket;
 	u32 kvno, enctype;
 	int ret, ec = 0;
 
@@ -197,24 +190,23 @@ int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
 		__be32 kvno;
 		__be32 enctype;
 		__be32 token_len;
-	} container;
+	} *container;
 
-	if (token_len < sizeof(container))
+	if (token_len < sizeof(*container))
 		goto short_packet;
 
 	/* 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)
-		goto short_packet;
+	container = token;
+	token += sizeof(*container);
 
-	kvno		= ntohl(container.kvno);
-	enctype		= ntohl(container.enctype);
-	ticket_len	= ntohl(container.token_len);
-	ticket_offset	= token_offset + sizeof(container);
+	kvno		= ntohl(container->kvno);
+	enctype		= ntohl(container->enctype);
+	ticket_len	= ntohl(container->token_len);
 
-	if (ticket_len > xdr_round_down(token_len - sizeof(container)))
+	if (ticket_len > xdr_round_down(token_len - sizeof(*container)))
 		goto short_packet;
 
 	_debug("KVNO %u", kvno);
@@ -237,8 +229,8 @@ int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
 	 * 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);
+	ticket = token;
+	ret = rxgk_decrypt(krb5, token_enc, &ticket, &ticket_len, &ec);
 	crypto_free_aead(token_enc);
 	token_enc = NULL;
 	if (ret < 0) {
@@ -248,7 +240,7 @@ int rxgk_extract_token(struct rxrpc_connection *conn, struct sk_buff *skb,
 		return ret;
 	}
 
-	ret = conn->security->default_decode_ticket(conn, skb, ticket_offset,
+	ret = conn->security->default_decode_ticket(conn, skb, ticket,
 						    ticket_len, _key);
 	if (ret < 0)
 		goto cant_get_token;
diff --git a/net/rxrpc/rxgk_common.h b/net/rxrpc/rxgk_common.h
index 1e257d7ab8ec..3deed5863f5a 100644
--- a/net/rxrpc/rxgk_common.h
+++ b/net/rxrpc/rxgk_common.h
@@ -41,10 +41,10 @@ struct rxgk_context {
  * rxgk_app.c
  */
 int rxgk_yfs_decode_ticket(struct rxrpc_connection *conn, struct sk_buff *skb,
-			   unsigned int ticket_offset, unsigned int ticket_len,
+			   void *ticket, 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,
+		       void *token, unsigned int token_len,
 		       struct key **_key);
 
 /*
@@ -62,31 +62,30 @@ int rxgk_set_up_token_cipher(const struct krb5_buffer *server_key,
 			     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
+ * Apply decryption and checksumming functions a flat data buffer.  The data
+ * point 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)
+static inline int rxgk_decrypt(const struct krb5_enctype *krb5,
+			       struct crypto_aead *aead,
+			       void **_data, unsigned int *_len,
+			       int *_error_code)
 {
-	struct scatterlist sg[16];
+	struct scatterlist sg[1];
 	size_t offset = 0, len = *_len;
-	int nr_sg, ret;
+	int 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;
+	sg_init_one(sg, *_data, len);
 
-	ret = crypto_krb5_decrypt(krb5, aead, sg, nr_sg,
-				  &offset, &len);
+	ret = crypto_krb5_decrypt(krb5, aead, sg, 1, &offset, &len);
 	switch (ret) {
 	case 0:
-		*_offset += offset;
+		if (offset & 3) {
+			*_error_code = RXGK_INCONSISTENCY;
+			ret = -EPROTO;
+			break;
+		}
+		*_data += offset;
 		*_len = len;
 		break;
 	case -EBADMSG: /* Checksum mismatch. */
@@ -106,31 +105,26 @@ int rxgk_decrypt_skb(const struct krb5_enctype *krb5,
 }
 
 /*
- * Check the MIC on a region of an skbuff.  The offset and length are updated
- * to reflect the actual content of the secure region.
+ * Check the MIC on a flat buffer.  The data pointer 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)
+int rxgk_verify_mic(const struct krb5_enctype *krb5,
+		    struct crypto_shash *shash,
+		    const struct krb5_buffer *metadata,
+		    void **_data, unsigned int *_len,
+		    u32 *_error_code)
 {
-	struct scatterlist sg[16];
+	struct scatterlist sg[1];
 	size_t offset = 0, len = *_len;
-	int nr_sg, ret;
+	int 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;
+	sg_init_one(sg, *_data, len);
 
-	ret = crypto_krb5_verify_mic(krb5, shash, metadata, sg, nr_sg,
-				     &offset, &len);
+	ret = crypto_krb5_verify_mic(krb5, shash, metadata, sg, 1, &offset, &len);
 	switch (ret) {
 	case 0:
-		*_offset += offset;
+		*_data += offset;
 		*_len = len;
 		break;
 	case -EBADMSG: /* Checksum mismatch */
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index cba7935977f0..6fbd883401ac 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -430,27 +430,25 @@ 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 rxkad_level1_hdr *sechdr;
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	struct rxrpc_crypt iv;
-	struct scatterlist sg[16];
-	u32 data_size, buf;
+	struct scatterlist sg[1];
+	void *data = call->rx_dec_buffer;
+	u32 len = sp->len, data_size, buf;
 	u16 check;
 	int ret;
 
 	_enter("");
 
-	if (sp->len < 8)
+	if (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;
+	sg_init_one(sg, data, len);
 
 	/* start the decryption afresh */
 	memset(&iv, 0, sizeof(iv));
@@ -464,13 +462,11 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 		return ret;
 
 	/* 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);
+	sechdr = data;
+	call->rx_dec_offset = sizeof(*sechdr);
+	len -= sizeof(*sechdr);
 
-	buf = ntohl(sechdr.data_size);
+	buf = ntohl(sechdr->data_size);
 	data_size = buf & 0xffff;
 
 	check = buf >> 16;
@@ -479,10 +475,10 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 	if (check != 0)
 		return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
 					  rxkad_abort_1_short_check);
-	if (data_size > sp->len)
+	if (data_size > len)
 		return rxrpc_abort_eproto(call, skb, RXKADDATALEN,
 					  rxkad_abort_1_short_data);
-	sp->len = data_size;
+	call->rx_dec_len = data_size;
 
 	_leave(" = 0 [dlen=%x]", data_size);
 	return 0;
@@ -496,43 +492,28 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 				 struct skcipher_request *req)
 {
 	const struct rxrpc_key_token *token;
-	struct rxkad_level2_hdr sechdr;
+	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;
+	struct scatterlist sg[1];
+	void *data = call->rx_dec_buffer;
+	u32 len = sp->len, data_size, buf;
 	u16 check;
-	int nsg, ret;
+	int ret;
 
-	_enter(",{%d}", sp->len);
+	_enter(",{%d}", len);
 
-	if (sp->len < 8)
+	if (len < 8)
 		return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
 					  rxkad_abort_2_short_header);
 
 	/* Don't let the crypto algo see a misaligned length. */
-	sp->len = round_down(sp->len, 8);
+	len = round_down(len, 8);
 
-	/* Decrypt the skbuff in-place.  TODO: We really want to decrypt
-	 * directly into the target buffer.
+	/* Decrypt in place in the call's decryption buffer.  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;
-	}
+	sg_init_one(sg, data, len);
 
 	/* decrypt from the session key */
 	token = call->conn->key->payload.data[0];
@@ -540,11 +521,9 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 
 	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);
+	skcipher_request_set_crypt(req, sg, sg, len, iv.x);
 	ret = crypto_skcipher_decrypt(req);
 	skcipher_request_zero(req);
-	if (sg != _sg)
-		kfree(sg);
 	if (ret < 0) {
 		if (ret == -ENOMEM)
 			return ret;
@@ -553,13 +532,11 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 	}
 
 	/* 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);
+	sechdr = data;
+	call->rx_dec_offset = sizeof(*sechdr);
+	len -= sizeof(*sechdr);
 
-	buf = ntohl(sechdr.data_size);
+	buf = ntohl(sechdr->data_size);
 	data_size = buf & 0xffff;
 
 	check = buf >> 16;
@@ -569,17 +546,18 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 		return rxrpc_abort_eproto(call, skb, RXKADSEALEDINCON,
 					  rxkad_abort_2_short_check);
 
-	if (data_size > sp->len)
+	if (data_size > len)
 		return rxrpc_abort_eproto(call, skb, RXKADDATALEN,
 					  rxkad_abort_2_short_data);
 
-	sp->len = data_size;
+	call->rx_dec_len = data_size;
 	_leave(" = 0 [dlen=%x]", data_size);
 	return 0;
 }
 
 /*
- * Verify the security on a received packet and the subpackets therein.
+ * Verify the security on a received (sub)packet.  If the packet needs
+ * modifying (e.g. decrypting), it must be copied.
  */
 static int rxkad_verify_packet(struct rxrpc_call *call, struct sk_buff *skb)
 {
@@ -985,7 +963,6 @@ static int rxkad_decrypt_ticket(struct rxrpc_connection *conn,
 	*_expiry = 0;
 
 	ASSERT(server_key->payload.data[0] != NULL);
-	ASSERTCMP((unsigned long) ticket & 7UL, ==, 0);
 
 	memcpy(&iv, &server_key->payload.data[2], sizeof(iv));
 
@@ -1134,14 +1111,15 @@ unlock:
  * verify a response
  */
 static int rxkad_verify_response(struct rxrpc_connection *conn,
-				 struct sk_buff *skb)
+				 struct sk_buff *skb,
+				 void *buffer, unsigned int len)
 {
 	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 = NULL;
+	void *ticket;
 	u32 version, kvno, ticket_len, level;
 	__be32 csum;
 	int ret, i;
@@ -1164,13 +1142,8 @@ static int rxkad_verify_response(struct rxrpc_connection *conn,
 		}
 	}
 
-	ret = -ENOMEM;
-	response = kzalloc_obj(struct rxkad_response, GFP_NOFS);
-	if (!response)
-		goto error;
-
-	if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
-			  response, sizeof(*response)) < 0) {
+	response = buffer;
+	if (len < sizeof(*response)) {
 		ret = rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
 				       rxkad_abort_resp_short);
 		goto error;
@@ -1182,6 +1155,9 @@ static int rxkad_verify_response(struct rxrpc_connection *conn,
 
 	trace_rxrpc_rx_response(conn, sp->hdr.serial, version, kvno, ticket_len);
 
+	buffer	+= sizeof(*response);
+	len	-= sizeof(*response);
+
 	if (version != RXKAD_VERSION) {
 		ret = rxrpc_abort_conn(conn, skb, RXKADINCONSISTENCY, -EPROTO,
 				       rxkad_abort_resp_version);
@@ -1201,13 +1177,8 @@ static int rxkad_verify_response(struct rxrpc_connection *conn,
 	}
 
 	/* extract the kerberos ticket and decrypt and decode it */
-	ret = -ENOMEM;
-	ticket = kmalloc(ticket_len, GFP_NOFS);
-	if (!ticket)
-		goto error;
-
-	if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header) + sizeof(*response),
-			  ticket, ticket_len) < 0) {
+	ticket = buffer;
+	if (ticket_len > len) {
 		ret = rxrpc_abort_conn(conn, skb, RXKADPACKETSHORT, -EPROTO,
 				       rxkad_abort_resp_short_tkt);
 		goto error;
@@ -1287,8 +1258,6 @@ static int rxkad_verify_response(struct rxrpc_connection *conn,
 	ret = rxrpc_get_server_data_key(conn, &session_key, expiry, kvno);
 
 error:
-	kfree(ticket);
-	kfree(response);
 	key_put(server_key);
 	_leave(" = %d", ret);
 	return ret;