net: introduce CAN specific pointer in the struct net_device

Since 20dd3850bcf8 ("can: Speed up CAN frame receiption by using
ml_priv") the CAN framework uses per device specific data in the AF_CAN
protocol. For this purpose the struct net_device->ml_priv is used. Later
the ml_priv usage in CAN was extended for other users, one of them being
CAN_J1939.

Later in the kernel ml_priv was converted to an union, used by other
drivers. E.g. the tun driver started storing it's stats pointer.

Since tun devices can claim to be a CAN device, CAN specific protocols
will wrongly interpret this pointer, which will cause system crashes.
Mostly this issue is visible in the CAN_J1939 stack.

To fix this issue, we request a dedicated CAN pointer within the
net_device struct.

Reported-by: syzbot+5138c4dd15a0401bec7b@syzkaller.appspotmail.com
Fixes: 20dd3850bcf8 ("can: Speed up CAN frame receiption by using ml_priv")
Fixes: ffd956eef69b ("can: introduce CAN midlayer private and allocate it automatically")
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Fixes: 497a5757ce4e ("tun: switch to net core provided statistics counters")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20210223070127.4538-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 45 insertions, 1 deletions

diff --git a/include/linux/can/can-ml.h b/include/linux/can/can-ml.h
index 2f5d731ae251..8afa92d15a66 100644
--- a/include/linux/can/can-ml.h
+++ b/include/linux/can/can-ml.h
@@ -44,6 +44,7 @@
 
 #include <linux/can.h>
 #include <linux/list.h>
+#include <linux/netdevice.h>
 
 #define CAN_SFF_RCV_ARRAY_SZ (1 << CAN_SFF_ID_BITS)
 #define CAN_EFF_RCV_HASH_BITS 10
@@ -65,4 +66,15 @@ struct can_ml_priv {
 #endif
 };
 
+static inline struct can_ml_priv *can_get_ml_priv(struct net_device *dev)
+{
+	return netdev_get_ml_priv(dev, ML_PRIV_CAN);
+}
+
+static inline void can_set_ml_priv(struct net_device *dev,
+				   struct can_ml_priv *ml_priv)
+{
+	netdev_set_ml_priv(dev, ml_priv, ML_PRIV_CAN);
+}
+
 #endif /* CAN_ML_H */
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index ddf4cfc12615..f06fbee8638e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1584,6 +1584,12 @@ enum netdev_priv_flags {
 #define IFF_L3MDEV_RX_HANDLER		IFF_L3MDEV_RX_HANDLER
 #define IFF_LIVE_RENAME_OK		IFF_LIVE_RENAME_OK
 
+/* Specifies the type of the struct net_device::ml_priv pointer */
+enum netdev_ml_priv_type {
+	ML_PRIV_NONE,
+	ML_PRIV_CAN,
+};
+
 /**
  *	struct net_device - The DEVICE structure.
  *
@@ -1779,6 +1785,7 @@ enum netdev_priv_flags {
  * 	@nd_net:		Network namespace this network device is inside
  *
  * 	@ml_priv:	Mid-layer private
+ *	@ml_priv_type:  Mid-layer private type
  * 	@lstats:	Loopback statistics
  * 	@tstats:	Tunnel statistics
  * 	@dstats:	Dummy statistics
@@ -2094,8 +2101,10 @@ struct net_device {
 	possible_net_t			nd_net;
 
 	/* mid-layer private */
+	void				*ml_priv;
+	enum netdev_ml_priv_type	ml_priv_type;
+
 	union {
-		void					*ml_priv;
 		struct pcpu_lstats __percpu		*lstats;
 		struct pcpu_sw_netstats __percpu	*tstats;
 		struct pcpu_dstats __percpu		*dstats;
@@ -2286,6 +2295,29 @@ static inline void netdev_reset_rx_headroom(struct net_device *dev)
 	netdev_set_rx_headroom(dev, -1);
 }
 
+static inline void *netdev_get_ml_priv(struct net_device *dev,
+				       enum netdev_ml_priv_type type)
+{
+	if (dev->ml_priv_type != type)
+		return NULL;
+
+	return dev->ml_priv;
+}
+
+static inline void netdev_set_ml_priv(struct net_device *dev,
+				      void *ml_priv,
+				      enum netdev_ml_priv_type type)
+{
+	WARN(dev->ml_priv_type && dev->ml_priv_type != type,
+	     "Overwriting already set ml_priv_type (%u) with different ml_priv_type (%u)!\n",
+	     dev->ml_priv_type, type);
+	WARN(!dev->ml_priv_type && dev->ml_priv,
+	     "Overwriting already set ml_priv and ml_priv_type is ML_PRIV_NONE!\n");
+
+	dev->ml_priv = ml_priv;
+	dev->ml_priv_type = type;
+}
+
 /*
  * Net namespace inlines
  */