can: skb: unify skb CAN frame identification helpers

Replace open coded checks for sk_buffs containing Classical CAN and
CAN FD frame structures as a preparation for CAN XL support.

With the added length check the unintended processing of CAN XL frames
having the CANXL_XLF bit set can be suppressed even when the skb->len
fits to non CAN XL frames.

The CAN_RAW socket needs a rework to use these helpers. Therefore the
use of these helpers is postponed to the CAN_RAW CAN XL integration.

The J1939 protocol gets a check for Classical CAN frames too.

Acked-by: Vincent Mailhol <[e-mail]>
Signed-off-by: Oliver Hartkopp <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]
Signed-off-by: Marc Kleine-Budde <[e-mail]>

drivers/net/can/dev/skb.c

···
 /* Drop a given socketbuffer if it does not contain a valid CAN frame. */
 bool can_dropped_invalid_skb(struct net_device *dev, struct sk_buff *skb)
 {
-	const struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
 	struct can_priv *priv = netdev_priv(dev);
 
-	if (skb->protocol == htons(ETH_P_CAN)) {
-		if (unlikely(skb->len != CAN_MTU ||
-			     cfd->len > CAN_MAX_DLEN))
+	switch (ntohs(skb->protocol)) {
+	case ETH_P_CAN:
+		if (!can_is_can_skb(skb))
 			goto inval_skb;
-	} else if (skb->protocol == htons(ETH_P_CANFD)) {
-		if (unlikely(skb->len != CANFD_MTU ||
-			     cfd->len > CANFD_MAX_DLEN))
+		break;
+
+	case ETH_P_CANFD:
+		if (!can_is_canfd_skb(skb))
 			goto inval_skb;
-	} else {
+		break;
+
+	default:
 		goto inval_skb;
 	}
 

include/linux/can/skb.h

···
 	return nskb;
 }
 
+static inline bool can_is_can_skb(const struct sk_buff *skb)
+{
+	struct can_frame *cf = (struct can_frame *)skb->data;
+
+	/* the CAN specific type of skb is identified by its data length */
+	return (skb->len == CAN_MTU && cf->len <= CAN_MAX_DLEN);
+}
+
 static inline bool can_is_canfd_skb(const struct sk_buff *skb)
 {
+	struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
+
 	/* the CAN specific type of skb is identified by its data length */
-	return skb->len == CANFD_MTU;
+	return (skb->len == CANFD_MTU && cfd->len <= CANFD_MAX_DLEN);
 }
 
 #endif /* !_CAN_SKB_H */

net/can/af_can.c

···
 int can_send(struct sk_buff *skb, int loop)
 {
 	struct sk_buff *newskb = NULL;
-	struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
 	struct can_pkg_stats *pkg_stats = dev_net(skb->dev)->can.pkg_stats;
 	int err = -EINVAL;
 
-	if (skb->len == CAN_MTU) {
+	if (can_is_can_skb(skb)) {
 		skb->protocol = htons(ETH_P_CAN);
-		if (unlikely(cfd->len > CAN_MAX_DLEN))
-			goto inval_skb;
-	} else if (skb->len == CANFD_MTU) {
+	} else if (can_is_canfd_skb(skb)) {
 		skb->protocol = htons(ETH_P_CANFD);
-		if (unlikely(cfd->len > CANFD_MAX_DLEN))
-			goto inval_skb;
 	} else {
 		goto inval_skb;
 	}
 
-	/* Make sure the CAN frame can pass the selected CAN netdevice.
-	 * As structs can_frame and canfd_frame are similar, we can provide
-	 * CAN FD frames to legacy CAN drivers as long as the length is <= 8
-	 */
-	if (unlikely(skb->len > skb->dev->mtu && cfd->len > CAN_MAX_DLEN)) {
+	/* Make sure the CAN frame can pass the selected CAN netdevice. */
+	if (unlikely(skb->len > skb->dev->mtu)) {
 		err = -EMSGSIZE;
 		goto inval_skb;
 	}
···
 static int can_rcv(struct sk_buff *skb, struct net_device *dev,
 		   struct packet_type *pt, struct net_device *orig_dev)
 {
-	struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
-
-	if (unlikely(dev->type != ARPHRD_CAN || skb->len != CAN_MTU)) {
+	if (unlikely(dev->type != ARPHRD_CAN || (!can_is_can_skb(skb)))) {
 		pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d\n",
 			     dev->type, skb->len);
-		goto free_skb;
-	}
 
-	/* This check is made separately since cfd->len would be uninitialized if skb->len = 0. */
-	if (unlikely(cfd->len > CAN_MAX_DLEN)) {
-		pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d, datalen %d\n",
-			     dev->type, skb->len, cfd->len);
-		goto free_skb;
+		kfree_skb(skb);
+		return NET_RX_DROP;
 	}
 
 	can_receive(skb, dev);
 	return NET_RX_SUCCESS;
-
-free_skb:
-	kfree_skb(skb);
-	return NET_RX_DROP;
 }
 
 static int canfd_rcv(struct sk_buff *skb, struct net_device *dev,
 		     struct packet_type *pt, struct net_device *orig_dev)
 {
-	struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
-
-	if (unlikely(dev->type != ARPHRD_CAN || skb->len != CANFD_MTU)) {
+	if (unlikely(dev->type != ARPHRD_CAN || (!can_is_canfd_skb(skb)))) {
 		pr_warn_once("PF_CAN: dropped non conform CAN FD skbuff: dev type %d, len %d\n",
 			     dev->type, skb->len);
-		goto free_skb;
-	}
 
-	/* This check is made separately since cfd->len would be uninitialized if skb->len = 0. */
-	if (unlikely(cfd->len > CANFD_MAX_DLEN)) {
-		pr_warn_once("PF_CAN: dropped non conform CAN FD skbuff: dev type %d, len %d, datalen %d\n",
-			     dev->type, skb->len, cfd->len);
-		goto free_skb;
+		kfree_skb(skb);
+		return NET_RX_DROP;
 	}
 
 	can_receive(skb, dev);
 	return NET_RX_SUCCESS;
-
-free_skb:
-	kfree_skb(skb);
-	return NET_RX_DROP;
 }
 
 /* af_can protocol functions */

net/can/bcm.c

···
 		return;
 
 	/* make sure to handle the correct frame type (CAN / CAN FD) */
-	if (skb->len != op->cfsiz)
-		return;
+	if (op->flags & CAN_FD_FRAME) {
+		if (!can_is_canfd_skb(skb))
+			return;
+	} else {
+		if (!can_is_can_skb(skb))
+			return;
+	}
 
 	/* disable timeout */
 	hrtimer_cancel(&op->timer);

net/can/gw.c

···
 
 	/* process strictly Classic CAN or CAN FD frames */
 	if (gwj->flags & CGW_FLAGS_CAN_FD) {
-		if (skb->len != CANFD_MTU)
+		if (!can_is_canfd_skb(skb))
 			return;
 	} else {
-		if (skb->len != CAN_MTU)
+		if (!can_is_can_skb(skb))
 			return;
 	}
 

net/can/isotp.c

···
 		if (cf->len <= CAN_MAX_DLEN) {
 			isotp_rcv_sf(sk, cf, SF_PCI_SZ4 + ae, skb, sf_dl);
 		} else {
-			if (skb->len == CANFD_MTU) {
+			if (can_is_canfd_skb(skb)) {
 				/* We have a CAN FD frame and CAN_DL is greater than 8:
 				 * Only frames with the SF_DL == 0 ESC value are valid.
 				 *

net/can/j1939/main.c

···
 	struct j1939_sk_buff_cb *skcb, *iskcb;
 	struct can_frame *cf;
 
+	/* make sure we only get Classical CAN frames */
+	if (!can_is_can_skb(iskb))
+		return;
+
 	/* create a copy of the skb
 	 * j1939 only delivers the real data bytes,
 	 * the header goes into sockaddr.