[RFC PATCH] can: isotp: add module parameter for maximum pdu size

[Oliver Hartkopp <socketcan@hartkopp.net>]

With ISO 15765-2:2016 the PDU size is not limited to 2^12 - 1 (4095) bytes
but can be represented as a 32 bit unsigned integer value which allows
2^32 - 1 bytes (~4GB). The use-cases like automotive unified diagnostic
services (UDS) and flashing of ECUs still use the small static buffers
which are provided at socket creation time.

When a use-case requires to transfer PDUs up to 1025 kByte the maximum
PDU size can now be extended by setting the module parameter max_pdu_size.
The extended size buffers are only allocated on a per-socket/connection
base when needed at run-time.

Link: https://github.com/raspberrypi/linux/issues/5371
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/isotp.c | 59 ++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 8 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 9bc344851704..3f052deeaaa0 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -83,14 +83,22 @@ MODULE_ALIAS("can-proto-6");
 			 (CAN_EFF_MASK | CAN_EFF_FLAG | CAN_RTR_FLAG) : \
 			 (CAN_SFF_MASK | CAN_EFF_FLAG | CAN_RTR_FLAG))
 
 /* ISO 15765-2:2016 supports more than 4095 byte per ISO PDU as the FF_DL can
  * take full 32 bit values (4 Gbyte). We would need some good concept to handle
- * this between user space and kernel space. For now increase the static buffer
- * to something about 64 kbyte to be able to test this new functionality.
+ * this between user space and kernel space. For now set the static buffer to
+ * something about 8 kbyte to be able to test this new functionality.
  */
-#define MAX_MSG_LENGTH 66000
+#define DEFAULT_MAX_PDU_SIZE 8300
+
+/* limit the isotp pdu size from the optional module parameter to 1MByte */
+#define MAX_PDU_SIZE (1025 * 1024U)
+
+static unsigned int max_pdu_size __read_mostly = DEFAULT_MAX_PDU_SIZE;
+module_param(max_pdu_size, uint, 0444);
+MODULE_PARM_DESC(max_pdu_size, "maximum isotp pdu size (default "
+		 __stringify(DEFAULT_MAX_PDU_SIZE) ")");
 
 /* N_PCI type values in bits 7-4 of N_PCI bytes */
 #define N_PCI_SF 0x00	/* single frame */
 #define N_PCI_FF 0x10	/* first frame */
 #define N_PCI_CF 0x20	/* consecutive frame */
@@ -121,17 +129,19 @@ enum {
 	ISOTP_WAIT_DATA,
 	ISOTP_SENDING
 };
 
 struct tpcon {
-	unsigned int idx;
+	u8 *buf;
+	unsigned int buflen;
 	unsigned int len;
+	unsigned int idx;
 	u32 state;
 	u8 bs;
 	u8 sn;
 	u8 ll_dl;
-	u8 buf[MAX_MSG_LENGTH + 1];
+	u8 sbuf[DEFAULT_MAX_PDU_SIZE];
 };
 
 struct isotp_sock {
 	struct sock sk;
 	int bound;
@@ -501,11 +511,21 @@ static int isotp_rcv_ff(struct sock *sk, struct canfd_frame *cf, int ae)
 	off = (so->rx.ll_dl > CAN_MAX_DLEN) ? 1 : 0;
 
 	if (so->rx.len + ae + off + ff_pci_sz < so->rx.ll_dl)
 		return 1;
 
-	if (so->rx.len > MAX_MSG_LENGTH) {
+	/* PDU size > default => try max_pdu_size */
+	if (so->rx.len > so->rx.buflen && so->rx.buflen < max_pdu_size) {
+		u8 *newbuf = kmalloc(max_pdu_size, GFP_ATOMIC);
+
+		if (newbuf) {
+			so->rx.buf = newbuf;
+			so->rx.buflen = max_pdu_size;
+		}
+	}
+
+	if (so->rx.len > so->rx.buflen) {
 		/* send FC frame with overflow status */
 		isotp_send_fc(sk, ae, ISOTP_FC_OVFLW);
 		return 1;
 	}
 
@@ -945,11 +965,21 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 			goto err_out;
 
 		so->tx.state = ISOTP_SENDING;
 	}
 
-	if (!size || size > MAX_MSG_LENGTH) {
+	/* PDU size > default => try max_pdu_size */
+	if (size > so->tx.buflen && so->tx.buflen < max_pdu_size) {
+		u8 *newbuf = kmalloc(max_pdu_size, GFP_KERNEL);
+
+		if (newbuf) {
+			so->tx.buf = newbuf;
+			so->tx.buflen = max_pdu_size;
+		}
+	}
+
+	if (!size || size > so->tx.buflen) {
 		err = -EINVAL;
 		goto err_out_drop;
 	}
 
 	/* take care of a potential SF_DL ESC offset for TX_DL > 8 */
@@ -1193,10 +1223,16 @@ static int isotp_release(struct socket *sock)
 	hrtimer_cancel(&so->rxtimer);
 
 	so->ifindex = 0;
 	so->bound = 0;
 
+	if (so->rx.buf != so->rx.sbuf)
+		kfree(so->rx.buf);
+
+	if (so->tx.buf != so->tx.sbuf)
+		kfree(so->tx.buf);
+
 	sock_orphan(sk);
 	sock->sk = NULL;
 
 	release_sock(sk);
 	sock_put(sk);
@@ -1589,10 +1625,15 @@ static int isotp_init(struct sock *sk)
 	so->tx.ll_dl = so->ll.tx_dl;
 
 	so->rx.state = ISOTP_IDLE;
 	so->tx.state = ISOTP_IDLE;
 
+	so->rx.buf = so->rx.sbuf;
+	so->tx.buf = so->tx.sbuf;
+	so->rx.buflen = DEFAULT_MAX_PDU_SIZE;
+	so->tx.buflen = DEFAULT_MAX_PDU_SIZE;
+
 	hrtimer_init(&so->rxtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
 	so->rxtimer.function = isotp_rx_timer_handler;
 	hrtimer_init(&so->txtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
 	so->txtimer.function = isotp_tx_timer_handler;
 	hrtimer_init(&so->txfrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
@@ -1656,11 +1697,13 @@ static struct notifier_block canisotp_notifier = {
 
 static __init int isotp_module_init(void)
 {
 	int err;
 
-	pr_info("can: isotp protocol\n");
+	max_pdu_size = min(max_pdu_size, (unsigned int)MAX_PDU_SIZE);
+
+	pr_info("can: isotp protocol (max_pdu_size %d)\n", max_pdu_size);
 
 	err = can_proto_register(&isotp_can_proto);
 	if (err < 0)
 		pr_err("can: registration of isotp protocol failed %pe\n", ERR_PTR(err));
 	else
-- 
2.30.2