Merge tag 'linux-can-fixes-for-6.16-20250722' of git://git.kernel.org/pub/scm/linux/kernel/git/mkl/linux-can

Marc Kleine-Budde says:

====================
pull-request: can 2025-07-22

The patch is by me and fixes a potential NULL pointer deref in the CAN
device driver infrastructure. It can be triggered from user space.

* tag 'linux-can-fixes-for-6.16-20250722' of git://git.kernel.org/pub/scm/linux/kernel/git/mkl/linux-can:
  can: netlink: can_changelink(): fix NULL pointer deref of struct can_priv::do_set_mode
====================

Link: https://patch.msgid.link/20250722110059.3664104-1-mkl@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

drivers/net/can/dev/dev.c

@@ -145,13 +145,16 @@ void can_change_state(struct net_device *dev, struct can_frame *cf,
 EXPORT_SYMBOL_GPL(can_change_state);
 
 /* CAN device restart for bus-off recovery */
-static void can_restart(struct net_device *dev)
+static int can_restart(struct net_device *dev)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	struct sk_buff *skb;
 	struct can_frame *cf;
 	int err;
 
+	if (!priv->do_set_mode)
+		return -EOPNOTSUPP;
+
 	if (netif_carrier_ok(dev))
 		netdev_err(dev, "Attempt to restart for bus-off recovery, but carrier is OK?\n");
 
@@ -173,10 +176,14 @@ static void can_restart(struct net_device *dev)
 	if (err) {
 		netdev_err(dev, "Restart failed, error %pe\n", ERR_PTR(err));
 		netif_carrier_off(dev);
+
+		return err;
 	} else {
 		netdev_dbg(dev, "Restarted\n");
 		priv->can_stats.restarts++;
 	}
+
+	return 0;
 }
 
 static void can_restart_work(struct work_struct *work)
@@ -201,9 +208,8 @@ int can_restart_now(struct net_device *dev)
 		return -EBUSY;
 
 	cancel_delayed_work_sync(&priv->restart_work);
-	can_restart(dev);
 
-	return 0;
+	return can_restart(dev);
 }
 
 /* CAN bus-off

drivers/net/can/dev/netlink.c

@@ -285,13 +285,25 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 	}
 
 	if (data[IFLA_CAN_RESTART_MS]) {
+		if (!priv->do_set_mode) {
+			NL_SET_ERR_MSG(extack,
+				       "Device doesn't support restart from Bus Off");
+			return -EOPNOTSUPP;
+		}
+
 		/* Do not allow changing restart delay while running */
 		if (dev->flags & IFF_UP)
 			return -EBUSY;
 		priv->restart_ms = nla_get_u32(data[IFLA_CAN_RESTART_MS]);
 	}
 
 	if (data[IFLA_CAN_RESTART]) {
+		if (!priv->do_set_mode) {
+			NL_SET_ERR_MSG(extack,
+				       "Device doesn't support restart from Bus Off");
+			return -EOPNOTSUPP;
+		}
+
 		/* Do not allow a restart while not running */
 		if (!(dev->flags & IFF_UP))
 			return -EINVAL;