[RFC PATCH v6 2/2] can: reject CAN FD content when disabled on CAN FD/XL interfaces

[Oliver Hartkopp <socketcan@hartkopp.net>]

The CAN XL devices can be configured as CAN XL only with 'xl on fd off'.
Also CAN FD interfaces can be configured to only support CAN CC 'fd off'.
Correctly reject CAN FD frames when FD is disabled for the outgoing CAN
FD/XL interfaces.

Virtual CAN interfaces (vcan, vxcan) are not affected as they have no such
CAN CC/FD/XL content configuration option.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 include/linux/can/dev.h | 12 ++++++++++++
 net/can/raw.c           | 12 +++++++-----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 9a92cbe5b2cb..9fa139cc793e 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -183,10 +183,22 @@ struct net_device *alloc_candev_mqs(int sizeof_priv, unsigned int echo_skb_max,
 void free_candev(struct net_device *dev);
 
 /* a candev safe wrapper around netdev_priv */
 struct can_priv *safe_candev_priv(struct net_device *dev);
 
+static inline bool can_dev_ctrlmode_fd_on(struct net_device *dev)
+{
+	struct can_priv *priv = safe_candev_priv(dev);
+
+	/* check ctrlmode on real CAN interfaces */
+	if (priv)
+		return (priv->ctrlmode & CAN_CTRLMODE_FD);
+
+	/* virtual CAN FD/XL interfaces always support CAN FD */
+	return true;
+}
+
 int open_candev(struct net_device *dev);
 void close_candev(struct net_device *dev);
 int can_change_mtu(struct net_device *dev, int new_mtu);
 int can_eth_ioctl_hwts(struct net_device *netdev, struct ifreq *ifr, int cmd);
 int can_ethtool_op_get_ts_info_hwts(struct net_device *dev,
diff --git a/net/can/raw.c b/net/can/raw.c
index e5e3952b0e09..d9df62e15ba4 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -879,24 +879,26 @@ static void raw_put_canxl_vcid(struct raw_sock *ro, struct sk_buff *skb)
 		cxl->prio &= CANXL_PRIO_MASK;
 		cxl->prio |= ro->tx_vcid_shifted;
 	}
 }
 
-static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb, int mtu)
+static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb,
+				      struct net_device *dev)
 {
 	/* Classical CAN -> no checks for flags and device capabilities */
 	if (can_is_can_skb(skb))
 		return CAN_MTU;
 
-	/* CAN FD -> needs to be enabled and a CAN FD or CAN XL device */
+	/* CAN FD -> needs to be enabled in a CAN FD or CAN XL device */
 	if (ro->fd_frames && can_is_canfd_skb_mtu_len(skb) &&
-	    (mtu == CANFD_MTU || can_is_canxl_dev_mtu(mtu)))
+	    (dev->mtu == CANFD_MTU || can_is_canxl_dev_mtu(dev->mtu)) &&
+	    can_dev_ctrlmode_fd_on(dev))
 		return CANFD_MTU;
 
 	/* CAN XL -> needs to be enabled and a CAN XL device */
 	if (ro->xl_frames && can_is_canxl_skb(skb) &&
-	    can_is_canxl_dev_mtu(mtu))
+	    can_is_canxl_dev_mtu(dev->mtu))
 		return CANXL_MTU;
 
 	return 0;
 }
 
@@ -948,11 +950,11 @@ static int raw_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 		goto free_skb;
 
 	err = -EINVAL;
 
 	/* check for valid CAN (CC/FD/XL) frame content */
-	txmtu = raw_check_txframe(ro, skb, dev->mtu);
+	txmtu = raw_check_txframe(ro, skb, dev);
 	if (!txmtu)
 		goto free_skb;
 
 	/* only CANXL: clear/forward/set VCID value */
 	if (txmtu == CANXL_MTU)
-- 
2.47.3