can: gw: add a variable limit for CAN frame routings
To prevent a possible misconfiguration (e.g. circular CAN frame routings)
limit the number of routings of a single CAN frame to a small variable value.
The limit can be specified by the module parameter 'max_hops' (1..6).
The default value is 1 (one hop), according to the original can-gw behaviour.
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/net/can/gw.c b/net/can/gw.c
index 37a3efb..4216a806 100644
--- a/net/can/gw.c
+++ b/net/can/gw.c
@@ -42,6 +42,7 @@
#include <linux/module.h>
#include <linux/init.h>
#include <linux/types.h>
+#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
@@ -58,14 +59,25 @@
#include <net/net_namespace.h>
#include <net/sock.h>
-#define CAN_GW_VERSION "20101209"
-static __initconst const char banner[] =
- KERN_INFO "can: netlink gateway (rev " CAN_GW_VERSION ")\n";
+#define CAN_GW_VERSION "20130117"
+#define CAN_GW_NAME "can-gw"
MODULE_DESCRIPTION("PF_CAN netlink gateway");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Oliver Hartkopp <oliver.hartkopp@volkswagen.de>");
-MODULE_ALIAS("can-gw");
+MODULE_ALIAS(CAN_GW_NAME);
+
+#define CGW_MIN_HOPS 1
+#define CGW_MAX_HOPS 6
+#define CGW_DEFAULT_HOPS 1
+
+static unsigned int max_hops __read_mostly = CGW_DEFAULT_HOPS;
+module_param(max_hops, uint, S_IRUGO);
+MODULE_PARM_DESC(max_hops,
+ "maximum " CAN_GW_NAME " routing hops for CAN frames "
+ "(valid values: " __stringify(CGW_MIN_HOPS) "-"
+ __stringify(CGW_MAX_HOPS) " hops, "
+ "default: " __stringify(CGW_DEFAULT_HOPS) ")");
static HLIST_HEAD(cgw_list);
static struct notifier_block notifier;
@@ -339,8 +351,23 @@
struct sk_buff *nskb;
int modidx = 0;
- /* do not handle already routed frames - see comment below */
- if (skb_mac_header_was_set(skb))
+ /*
+ * Do not handle CAN frames routed more than 'max_hops' times.
+ * In general we should never catch this delimiter which is intended
+ * to cover a misconfiguration protection (e.g. circular CAN routes).
+ *
+ * The Controller Area Network controllers only accept CAN frames with
+ * correct CRCs - which are not visible in the controller registers.
+ * According to skbuff.h documentation the csum_start element for IP
+ * checksums is undefined/unsued when ip_summed == CHECKSUM_UNNECESSARY.
+ * Only CAN skbs can be processed here which already have this property.
+ */
+
+#define cgw_hops(skb) ((skb)->csum_start)
+
+ BUG_ON(skb->ip_summed != CHECKSUM_UNNECESSARY);
+
+ if (cgw_hops(skb) >= max_hops)
return;
if (!(gwj->dst.dev->flags & IFF_UP)) {
@@ -371,15 +398,8 @@
return;
}
- /*
- * Mark routed frames by setting some mac header length which is
- * not relevant for the CAN frames located in the skb->data section.
- *
- * As dev->header_ops is not set in CAN netdevices no one is ever
- * accessing the various header offsets in the CAN skbuffs anyway.
- * E.g. using the packet socket to read CAN frames is still working.
- */
- skb_set_mac_header(nskb, 8);
+ /* put the incremented hop counter in the cloned skb */
+ cgw_hops(nskb) = cgw_hops(skb) + 1;
nskb->dev = gwj->dst.dev;
/* pointer to modifiable CAN frame */
@@ -903,7 +923,11 @@
static __init int cgw_module_init(void)
{
- printk(banner);
+ /* sanitize given module parameter */
+ max_hops = clamp_t(unsigned int, max_hops, CGW_MIN_HOPS, CGW_MAX_HOPS);
+
+ pr_info("can: netlink gateway (rev " CAN_GW_VERSION ") max_hops=%d\n",
+ max_hops);
cgw_cache = kmem_cache_create("can_gw", sizeof(struct cgw_job),
0, 0, NULL);
