On 01/07/2013 10:51 PM, Oliver Hartkopp wrote: > 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 > > --- > > Having the possibility of only a single CAN frame routing (one hop) hinders > use-cases for some complex application setups. To enable more than one CAN > frame routing process with a single CAN frame (skb) a counter needed to be > implemented to prevent an endless frame processing (e.g. due to some kind of > misconfiguration). > > As the skb control buffer (cb) potentially gets modified by net/sched in the > tx path the csum element for IP checksums is re-used for the counter, as CAN > frame skbs (ARPHRD_CAN) never contain any kind of checksums (see src comment). > > @Marc: I wanted to sent this patch on netdev ML to see if there are any > objections of using skb->csum in the way i proposed here. When the patch is > fine please take it via can-next for this net-next cycle then. Tnx. Fine with me. I'll take the patch as usual, once it's ready. See a nitpick inline. > diff --git a/include/uapi/linux/can/gw.h b/include/uapi/linux/can/gw.h > index 8e1db18..ba87697 100644 > --- a/include/uapi/linux/can/gw.h > +++ b/include/uapi/linux/can/gw.h > @@ -44,6 +44,7 @@ enum { > CGW_SRC_IF, /* ifindex of source network interface */ > CGW_DST_IF, /* ifindex of destination network interface */ > CGW_FILTER, /* specify struct can_filter on source CAN device */ > + CGW_DELETED, /* number of deleted CAN frames (see max_hops param) */ > __CGW_MAX > }; > > diff --git a/net/can/gw.c b/net/can/gw.c > index 574dda78e..20d5a7d 100644 > --- a/net/can/gw.c > +++ b/net/can/gw.c > @@ -57,15 +57,23 @@ > #include > #include > > -#define CAN_GW_VERSION "20101209" > +#define CAN_GW_VERSION "20130107" > static __initconst const char banner[] = > - KERN_INFO "can: netlink gateway (rev " CAN_GW_VERSION ")\n"; > + KERN_INFO "can: netlink gateway (rev " CAN_GW_VERSION ")"; > > MODULE_DESCRIPTION("PF_CAN netlink gateway"); > MODULE_LICENSE("Dual BSD/GPL"); > MODULE_AUTHOR("Oliver Hartkopp "); > MODULE_ALIAS("can-gw"); > > +#define CAN_GW_MAX_HOPS 6 > + > +static unsigned int max_hops __read_mostly = 1; > +module_param(max_hops, uint, S_IRUGO); > +MODULE_PARM_DESC(max_hops, > + "maximum can-gw routing hops for CAN frames " > + "(valid values: 1-6 hops, default: 1)"); > + > static HLIST_HEAD(cgw_list); > static struct notifier_block notifier; > > @@ -118,6 +126,7 @@ struct cgw_job { > struct rcu_head rcu; > u32 handled_frames; > u32 dropped_frames; > + u32 deleted_frames; > struct cf_mod mod; > union { > /* CAN frame data source */ > @@ -338,9 +347,27 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data) > 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 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) > + > + BUG_ON(skb->ip_summed != CHECKSUM_UNNECESSARY); > + > + if (cgw_hops(skb) >= max_hops) { > + /* indicate deleted frames due to misconfiguration */ > + gwj->deleted_frames++; > return; > + } > > if (!(gwj->dst.dev->flags & IFF_UP)) { > gwj->dropped_frames++; > @@ -363,15 +390,8 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data) > 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 */ > @@ -472,6 +492,11 @@ static int cgw_put_job(struct sk_buff *skb, struct cgw_job *gwj, int type, > goto cancel; > } > > + if (gwj->deleted_frames) { > + if (nla_put_u32(skb, CGW_DELETED, gwj->deleted_frames) < 0) > + goto cancel; > + } > + > /* check non default settings of attributes */ > > if (gwj->mod.modtype.and) { > @@ -771,6 +796,7 @@ static int cgw_create_job(struct sk_buff *skb, struct nlmsghdr *nlh, > > gwj->handled_frames = 0; > gwj->dropped_frames = 0; > + gwj->deleted_frames = 0; > gwj->flags = r->flags; > gwj->gwtype = r->gwtype; > > @@ -895,7 +921,14 @@ static int cgw_remove_job(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg) > > static __init int cgw_module_init(void) > { > - printk(banner); > + /* sanitize given module parameter */ > + if (max_hops < 1) > + max_hops = 1; > + > + if (max_hops > CAN_GW_MAX_HOPS) > + max_hops = CAN_GW_MAX_HOPS; You can make use of clamp(val, min, max) here. > + > + printk("%s max_hops=%d\n", banner, max_hops); > > cgw_cache = kmem_cache_create("can_gw", sizeof(struct cgw_job), > 0, 0, NULL); Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |