[PATCH] can: raw: instantly reject unsupported CAN frames

[Oliver Hartkopp <socketcan@hartkopp.net>]

For real CAN interfaces the CAN_CTRLMODE_FD and CAN_CTRLMODE_XL control
modes indicate whether an interface can handle those CAN FD/XL frames.

In the case a CAN XL interface is configured in CANXL-only mode with
disabled error-signalling neither CAN CC nor CAN FD frames can be sent.

The checks are performed on CAN_RAW sockets to give an instant feedback
to the user when writing unsupported CAN frames to the interface.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 include/linux/can/dev.h | 12 +++++++++
 net/can/raw.c           | 54 +++++++++++++++++++++++++++++++++++------
 2 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 945c16743702..9c00bfd077bf 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -129,10 +129,22 @@ int can_restart_now(struct net_device *dev);
 void can_bus_off(struct net_device *dev);
 
 const char *can_get_state_str(const enum can_state state);
 const char *can_get_ctrlmode_str(u32 ctrlmode);
 
+static inline bool can_dev_err_signal_is_disabled(struct can_priv *priv)
+{
+	const u32 mixed_mode = CAN_CTRLMODE_FD | CAN_CTRLMODE_XL;
+
+	/* When CAN XL is enabled but FD is disabled we are running in
+	 * the so-called 'XL-only mode' where the error signalling is
+	 * disabled.
+	 * The so-called CC/FD/XL 'mixed mode' requires error signalling.
+	 */
+	return ((priv->ctrlmode & mixed_mode) == CAN_CTRLMODE_XL);
+}
+
 /* drop skb if it does not contain a valid CAN frame for sending */
 static inline bool can_dev_dropped_skb(struct net_device *dev, struct sk_buff *skb)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	u32 silent_mode = priv->ctrlmode & (CAN_CTRLMODE_LISTENONLY |
diff --git a/net/can/raw.c b/net/can/raw.c
index a53853f5e9af..c7311f27e913 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -890,24 +890,62 @@ 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 inline bool raw_dev_cc_enabled(struct net_device *dev,
+				      struct can_priv *priv)
 {
-	/* Classical CAN -> no checks for flags and device capabilities */
-	if (can_is_can_skb(skb))
+	/* The CANXL-only mode disables error-signalling on the CAN bus
+	 * which is needed to send CAN CC/FD frames
+	 */
+	if (priv)
+		return !can_dev_err_signal_is_disabled(priv);
+
+	/* virtual CAN interfaces always support CAN CC */
+	return true;
+}
+
+static inline bool raw_dev_fd_enabled(struct net_device *dev,
+				      struct can_priv *priv)
+{
+	/* check FD ctrlmode on real CAN interfaces */
+	if (priv)
+		return (priv->ctrlmode & CAN_CTRLMODE_FD);
+
+	/* check MTU for virtual CAN FD interfaces */
+	return (READ_ONCE(dev->mtu) >= CANFD_MTU);
+}
+
+static inline bool raw_dev_xl_enabled(struct net_device *dev,
+				      struct can_priv *priv)
+{
+	/* check XL ctrlmode on real CAN interfaces */
+	if (priv)
+		return (priv->ctrlmode & CAN_CTRLMODE_XL);
+
+	/* check MTU for virtual CAN XL interfaces */
+	return can_is_canxl_dev_mtu(READ_ONCE(dev->mtu));
+}
+
+static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb,
+				      struct net_device *dev)
+{
+	struct can_priv *priv = safe_candev_priv(dev);
+
+	/* Classical CAN */
+	if (can_is_can_skb(skb) && raw_dev_cc_enabled(dev, priv))
 		return CAN_MTU;
 
-	/* CAN FD -> needs to be enabled and a CAN FD or CAN XL device */
+	/* CAN FD */
 	if (ro->fd_frames && can_is_canfd_skb(skb) &&
-	    (mtu == CANFD_MTU || can_is_canxl_dev_mtu(mtu)))
+	    raw_dev_fd_enabled(dev, priv))
 		return CANFD_MTU;
 
-	/* CAN XL -> needs to be enabled and a CAN XL device */
+	/* CAN XL */
 	if (ro->xl_frames && can_is_canxl_skb(skb) &&
-	    can_is_canxl_dev_mtu(mtu))
+	    raw_dev_xl_enabled(dev, priv))
 		return CANXL_MTU;
 
 	return 0;
 }
 
@@ -959,11 +997,11 @@ 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, READ_ONCE(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