rxrpc: Fix -Wframe-larger-than= warnings from on-stack crypto

rxkad sometimes triggers a warning about oversized stack frames when
building with clang for a 32-bit architecture:

net/rxrpc/rxkad.c:243:12: error: stack frame size of 1088 bytes in function 'rxkad_secure_packet' [-Werror,-Wframe-larger-than=]
net/rxrpc/rxkad.c:501:12: error: stack frame size of 1088 bytes in function 'rxkad_verify_packet' [-Werror,-Wframe-larger-than=]

The problem is the combination of SYNC_SKCIPHER_REQUEST_ON_STACK() in
rxkad_verify_packet()/rxkad_secure_packet() with the relatively large
scatterlist in rxkad_verify_packet_1()/rxkad_secure_packet_encrypt().

The warning does not show up when using gcc, which does not inline the
functions as aggressively, but the problem is still the same.

Allocate the cipher buffers from the slab instead, caching the allocated
packet crypto request memory used for DATA packet crypto in the rxrpc_call
struct.

Fixes: 17926a7 ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rxrpc/ar-internal.h

@@ -226,6 +226,9 @@ struct rxrpc_security {
 	int (*verify_packet)(struct rxrpc_call *, struct sk_buff *,
 			     unsigned int, unsigned int, rxrpc_seq_t, u16);
 
+	/* Free crypto request on a call */
+	void (*free_call_crypto)(struct rxrpc_call *);
+
 	/* Locate the data in a received packet that has been verified. */
 	void (*locate_data)(struct rxrpc_call *, struct sk_buff *,
 			    unsigned int *, unsigned int *);
@@ -557,6 +560,7 @@ struct rxrpc_call {
 	unsigned long		expect_term_by;	/* When we expect call termination by */
 	u32			next_rx_timo;	/* Timeout for next Rx packet (jif) */
 	u32			next_req_timo;	/* Timeout for next Rx request packet (jif) */
+	struct skcipher_request	*cipher_req;	/* Packet cipher request buffer */
 	struct timer_list	timer;		/* Combined event timer */
 	struct work_struct	processor;	/* Event processor */
 	rxrpc_notify_rx_t	notify_rx;	/* kernel service Rx notification function */

net/rxrpc/call_object.c

@@ -476,8 +476,10 @@ void rxrpc_release_call(struct rxrpc_sock *rx, struct rxrpc_call *call)
 
 	_debug("RELEASE CALL %p (%d CONN %p)", call, call->debug_id, conn);
 
-	if (conn)
+	if (conn) {
 		rxrpc_disconnect_call(call);
+		conn->security->free_call_crypto(call);
+	}
 
 	for (i = 0; i < RXRPC_RXTX_BUFF_SIZE; i++) {
 		rxrpc_free_skb(call->rxtx_buffer[i],

net/rxrpc/insecure.c

@@ -33,6 +33,10 @@ static int none_verify_packet(struct rxrpc_call *call, struct sk_buff *skb,
 	return 0;
 }
 
+static void none_free_call_crypto(struct rxrpc_call *call)
+{
+}
+
 static void none_locate_data(struct rxrpc_call *call, struct sk_buff *skb,
 			     unsigned int *_offset, unsigned int *_len)
 {
@@ -83,6 +87,7 @@ const struct rxrpc_security rxrpc_no_security = {
 	.exit				= none_exit,
 	.init_connection_security	= none_init_connection_security,
 	.prime_packet_security		= none_prime_packet_security,
+	.free_call_crypto		= none_free_call_crypto,
 	.secure_packet			= none_secure_packet,
 	.verify_packet			= none_verify_packet,
 	.locate_data			= none_locate_data,

net/rxrpc/rxkad.c

@@ -43,6 +43,7 @@ struct rxkad_level2_hdr {
  * packets
  */
 static struct crypto_sync_skcipher *rxkad_ci;
+static struct skcipher_request *rxkad_ci_req;
 static DEFINE_MUTEX(rxkad_ci_mutex);
 
 /*
@@ -99,8 +100,8 @@ static int rxkad_init_connection_security(struct rxrpc_connection *conn)
  */
 static int rxkad_prime_packet_security(struct rxrpc_connection *conn)
 {
+	struct skcipher_request *req;
 	struct rxrpc_key_token *token;
-	SYNC_SKCIPHER_REQUEST_ON_STACK(req, conn->cipher);
 	struct scatterlist sg;
 	struct rxrpc_crypt iv;
 	__be32 *tmpbuf;
@@ -115,6 +116,12 @@ static int rxkad_prime_packet_security(struct rxrpc_connection *conn)
 	if (!tmpbuf)
 		return -ENOMEM;
 
+	req = skcipher_request_alloc(&conn->cipher->base, GFP_NOFS);
+	if (!req) {
+		kfree(tmpbuf);
+		return -ENOMEM;
+	}
+
 	token = conn->params.key->payload.data[0];
 	memcpy(&iv, token->kad->session_key, sizeof(iv));
 
@@ -128,14 +135,43 @@ static int rxkad_prime_packet_security(struct rxrpc_connection *conn)
 	skcipher_request_set_callback(req, 0, NULL, NULL);
 	skcipher_request_set_crypt(req, &sg, &sg, tmpsize, iv.x);
 	crypto_skcipher_encrypt(req);
-	skcipher_request_zero(req);
+	skcipher_request_free(req);
 
 	memcpy(&conn->csum_iv, tmpbuf + 2, sizeof(conn->csum_iv));
 	kfree(tmpbuf);
 	_leave(" = 0");
 	return 0;
 }
 
+/*
+ * Allocate and prepare the crypto request on a call.  For any particular call,
+ * this is called serially for the packets, so no lock should be necessary.
+ */
+static struct skcipher_request *rxkad_get_call_crypto(struct rxrpc_call *call)
+{
+	struct crypto_skcipher *tfm = &call->conn->cipher->base;
+	struct skcipher_request	*cipher_req = call->cipher_req;
+
+	if (!cipher_req) {
+		cipher_req = skcipher_request_alloc(tfm, GFP_NOFS);
+		if (!cipher_req)
+			return NULL;
+		call->cipher_req = cipher_req;
+	}
+
+	return cipher_req;
+}
+
+/*
+ * Clean up the crypto on a call.
+ */
+static void rxkad_free_call_crypto(struct rxrpc_call *call)
+{
+	if (call->cipher_req)
+		skcipher_request_free(call->cipher_req);
+	call->cipher_req = NULL;
+}
+
 /*
  * partially encrypt a packet (level 1 security)
  */
@@ -246,7 +282,7 @@ static int rxkad_secure_packet(struct rxrpc_call *call,
 			       void *sechdr)
 {
 	struct rxrpc_skb_priv *sp;
-	SYNC_SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
+	struct skcipher_request	*req;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg;
 	u32 x, y;
@@ -265,6 +301,10 @@ static int rxkad_secure_packet(struct rxrpc_call *call,
 	if (ret < 0)
 		return ret;
 
+	req = rxkad_get_call_crypto(call);
+	if (!req)
+		return -ENOMEM;
+
 	/* continue encrypting from where we left off */
 	memcpy(&iv, call->conn->csum_iv.x, sizeof(iv));
 
@@ -502,7 +542,7 @@ static int rxkad_verify_packet(struct rxrpc_call *call, struct sk_buff *skb,
 			       unsigned int offset, unsigned int len,
 			       rxrpc_seq_t seq, u16 expected_cksum)
 {
-	SYNC_SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
+	struct skcipher_request	*req;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg;
 	bool aborted;
@@ -515,6 +555,10 @@ static int rxkad_verify_packet(struct rxrpc_call *call, struct sk_buff *skb,
 	if (!call->conn->cipher)
 		return 0;
 
+	req = rxkad_get_call_crypto(call);
+	if (!req)
+		return -ENOMEM;
+
 	/* continue encrypting from where we left off */
 	memcpy(&iv, call->conn->csum_iv.x, sizeof(iv));
 
@@ -747,14 +791,18 @@ static void rxkad_calc_response_checksum(struct rxkad_response *response)
 /*
  * encrypt the response packet
  */
-static void rxkad_encrypt_response(struct rxrpc_connection *conn,
-				   struct rxkad_response *resp,
-				   const struct rxkad_key *s2)
+static int rxkad_encrypt_response(struct rxrpc_connection *conn,
+				  struct rxkad_response *resp,
+				  const struct rxkad_key *s2)
 {
-	SYNC_SKCIPHER_REQUEST_ON_STACK(req, conn->cipher);
+	struct skcipher_request *req;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[1];
 
+	req = skcipher_request_alloc(&conn->cipher->base, GFP_NOFS);
+	if (!req)
+		return -ENOMEM;
+
 	/* continue encrypting from where we left off */
 	memcpy(&iv, s2->session_key, sizeof(iv));
 
@@ -764,7 +812,8 @@ static void rxkad_encrypt_response(struct rxrpc_connection *conn,
 	skcipher_request_set_callback(req, 0, NULL, NULL);
 	skcipher_request_set_crypt(req, sg, sg, sizeof(resp->encrypted), iv.x);
 	crypto_skcipher_encrypt(req);
-	skcipher_request_zero(req);
+	skcipher_request_free(req);
+	return 0;
 }
 
 /*
@@ -839,8 +888,9 @@ static int rxkad_respond_to_challenge(struct rxrpc_connection *conn,
 
 	/* calculate the response checksum and then do the encryption */
 	rxkad_calc_response_checksum(resp);
-	rxkad_encrypt_response(conn, resp, token->kad);
-	ret = rxkad_send_response(conn, &sp->hdr, resp, token->kad);
+	ret = rxkad_encrypt_response(conn, resp, token->kad);
+	if (ret == 0)
+		ret = rxkad_send_response(conn, &sp->hdr, resp, token->kad);
 	kfree(resp);
 	return ret;
 
@@ -1017,18 +1067,16 @@ static void rxkad_decrypt_response(struct rxrpc_connection *conn,
 				   struct rxkad_response *resp,
 				   const struct rxrpc_crypt *session_key)
 {
-	SYNC_SKCIPHER_REQUEST_ON_STACK(req, rxkad_ci);
+	struct skcipher_request *req = rxkad_ci_req;
 	struct scatterlist sg[1];
 	struct rxrpc_crypt iv;
 
 	_enter(",,%08x%08x",
 	       ntohl(session_key->n[0]), ntohl(session_key->n[1]));
 
-	ASSERT(rxkad_ci != NULL);
-
 	mutex_lock(&rxkad_ci_mutex);
 	if (crypto_sync_skcipher_setkey(rxkad_ci, session_key->x,
-				   sizeof(*session_key)) < 0)
+					sizeof(*session_key)) < 0)
 		BUG();
 
 	memcpy(&iv, session_key, sizeof(iv));
@@ -1222,19 +1270,35 @@ static void rxkad_clear(struct rxrpc_connection *conn)
  */
 static int rxkad_init(void)
 {
+	struct crypto_sync_skcipher *tfm;
+	struct skcipher_request *req;
+
 	/* pin the cipher we need so that the crypto layer doesn't invoke
 	 * keventd to go get it */
-	rxkad_ci = crypto_alloc_sync_skcipher("pcbc(fcrypt)", 0, 0);
-	return PTR_ERR_OR_ZERO(rxkad_ci);
+	tfm = crypto_alloc_sync_skcipher("pcbc(fcrypt)", 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	req = skcipher_request_alloc(&tfm->base, GFP_KERNEL);
+	if (!req)
+		goto nomem_tfm;
+
+	rxkad_ci_req = req;
+	rxkad_ci = tfm;
+	return 0;
+
+nomem_tfm:
+	crypto_free_sync_skcipher(tfm);
+	return -ENOMEM;
 }
 
 /*
  * Clean up the rxkad security service.
  */
 static void rxkad_exit(void)
 {
-	if (rxkad_ci)
-		crypto_free_sync_skcipher(rxkad_ci);
+	crypto_free_sync_skcipher(rxkad_ci);
+	skcipher_request_free(rxkad_ci_req);
 }
 
 /*
@@ -1249,6 +1313,7 @@ const struct rxrpc_security rxkad = {
 	.prime_packet_security		= rxkad_prime_packet_security,
 	.secure_packet			= rxkad_secure_packet,
 	.verify_packet			= rxkad_verify_packet,
+	.free_call_crypto		= rxkad_free_call_crypto,
 	.locate_data			= rxkad_locate_data,
 	.issue_challenge		= rxkad_issue_challenge,
 	.respond_to_challenge		= rxkad_respond_to_challenge,