netdev - [PATCH net 3/4] can: raw: instantly reject disabled CAN frames

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Message-ID: <20260114105212.1034554-4-mkl@pengutronix.de>
Date: Wed, 14 Jan 2026 11:45:02 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	kuba@...nel.org,
	linux-can@...r.kernel.org,
	kernel@...gutronix.de,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Arnd Bergmann <arnd@...db.de>,
	Vincent Mailhol <mailhol@...nel.org>
Subject: [PATCH net 3/4] can: raw: instantly reject disabled CAN frames

From: Oliver Hartkopp <socketcan@...tkopp.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 now performed on CAN_RAW sockets to give an instant feedback
to the user when writing unsupported CAN frames to the interface or when
the CAN interface is in read-only mode.

Fixes: 1a620a723853 ("can: raw: instantly reject unsupported CAN frames")
Cc: Marc Kleine-Budde <mkl@...gutronix.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Vincent Mailhol <mailhol@...nel.org>
Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.net>
Link: https://patch.msgid.link/20260109144135.8495-4-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 net/can/raw.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/net/can/raw.c b/net/can/raw.c
index f36a83d3447c..d66036da6753 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -49,8 +49,8 @@
 #include <linux/if_arp.h>
 #include <linux/skbuff.h>
 #include <linux/can.h>
+#include <linux/can/can-ml.h>
 #include <linux/can/core.h>
-#include <linux/can/dev.h> /* for can_is_canxl_dev_mtu() */
 #include <linux/can/skb.h>
 #include <linux/can/raw.h>
 #include <net/sock.h>
@@ -892,20 +892,21 @@ static void raw_put_canxl_vcid(struct raw_sock *ro, struct sk_buff *skb)
 	}
 }
 
-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))
+	/* Classical CAN */
+	if (can_is_can_skb(skb) && can_cap_enabled(dev, CAN_CAP_CC))
 		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)))
+	    can_cap_enabled(dev, CAN_CAP_FD))
 		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))
+	    can_cap_enabled(dev, CAN_CAP_XL))
 		return CANXL_MTU;
 
 	return 0;
@@ -944,6 +945,10 @@ static int raw_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if (!dev)
 		return -ENXIO;
 
+	/* no sending on a CAN device in read-only mode */
+	if (can_cap_enabled(dev, CAN_CAP_RO))
+		return -EACCES;
+
 	skb = sock_alloc_send_skb(sk, size + sizeof(struct can_skb_priv),
 				  msg->msg_flags & MSG_DONTWAIT, &err);
 	if (!skb)
@@ -961,7 +966,7 @@ static int raw_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	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;
 
-- 
2.51.0