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>
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56
net/can/gw.c
56
net/can/gw.c
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@ -42,6 +42,7 @@
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/list.h>
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#include <linux/spinlock.h>
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#include <linux/rcupdate.h>
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@ -58,14 +59,25 @@
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#include <net/net_namespace.h>
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#include <net/sock.h>
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#define CAN_GW_VERSION "20101209"
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static __initconst const char banner[] =
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KERN_INFO "can: netlink gateway (rev " CAN_GW_VERSION ")\n";
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#define CAN_GW_VERSION "20130117"
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#define CAN_GW_NAME "can-gw"
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MODULE_DESCRIPTION("PF_CAN netlink gateway");
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MODULE_LICENSE("Dual BSD/GPL");
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MODULE_AUTHOR("Oliver Hartkopp <oliver.hartkopp@volkswagen.de>");
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MODULE_ALIAS("can-gw");
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MODULE_ALIAS(CAN_GW_NAME);
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#define CGW_MIN_HOPS 1
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#define CGW_MAX_HOPS 6
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#define CGW_DEFAULT_HOPS 1
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static unsigned int max_hops __read_mostly = CGW_DEFAULT_HOPS;
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module_param(max_hops, uint, S_IRUGO);
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MODULE_PARM_DESC(max_hops,
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"maximum " CAN_GW_NAME " routing hops for CAN frames "
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"(valid values: " __stringify(CGW_MIN_HOPS) "-"
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__stringify(CGW_MAX_HOPS) " hops, "
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"default: " __stringify(CGW_DEFAULT_HOPS) ")");
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static HLIST_HEAD(cgw_list);
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static struct notifier_block notifier;
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@ -339,8 +351,23 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data)
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struct sk_buff *nskb;
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int modidx = 0;
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/* do not handle already routed frames - see comment below */
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if (skb_mac_header_was_set(skb))
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/*
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* Do not handle CAN frames routed more than 'max_hops' times.
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* In general we should never catch this delimiter which is intended
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* to cover a misconfiguration protection (e.g. circular CAN routes).
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*
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* The Controller Area Network controllers only accept CAN frames with
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* correct CRCs - which are not visible in the controller registers.
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* According to skbuff.h documentation the csum_start element for IP
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* checksums is undefined/unsued when ip_summed == CHECKSUM_UNNECESSARY.
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* Only CAN skbs can be processed here which already have this property.
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*/
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#define cgw_hops(skb) ((skb)->csum_start)
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BUG_ON(skb->ip_summed != CHECKSUM_UNNECESSARY);
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if (cgw_hops(skb) >= max_hops)
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return;
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if (!(gwj->dst.dev->flags & IFF_UP)) {
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@ -371,15 +398,8 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data)
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return;
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}
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/*
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* Mark routed frames by setting some mac header length which is
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* not relevant for the CAN frames located in the skb->data section.
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*
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* As dev->header_ops is not set in CAN netdevices no one is ever
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* accessing the various header offsets in the CAN skbuffs anyway.
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* E.g. using the packet socket to read CAN frames is still working.
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*/
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skb_set_mac_header(nskb, 8);
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/* put the incremented hop counter in the cloned skb */
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cgw_hops(nskb) = cgw_hops(skb) + 1;
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nskb->dev = gwj->dst.dev;
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/* pointer to modifiable CAN frame */
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@ -903,7 +923,11 @@ static int cgw_remove_job(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
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static __init int cgw_module_init(void)
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{
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printk(banner);
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/* sanitize given module parameter */
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max_hops = clamp_t(unsigned int, max_hops, CGW_MIN_HOPS, CGW_MAX_HOPS);
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pr_info("can: netlink gateway (rev " CAN_GW_VERSION ") max_hops=%d\n",
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max_hops);
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cgw_cache = kmem_cache_create("can_gw", sizeof(struct cgw_job),
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0, 0, NULL);
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