From 3ffecc14ec7ee8eb941e50c0076798a042924c62 Mon Sep 17 00:00:00 2001 From: Oliver Hartkopp Date: Sun, 1 Feb 2026 15:33:21 +0100 Subject: [PATCH] can: gw: use can_gw_hops instead of sk_buff::csum_start As CAN skbs don't use IP checksums the skb->csum_start variable was used to store the can-gw CAN frame time-to-live counter together with skb->ip_summed set to CHECKSUM_UNNECESSARY. Remove the 'hack' using the skb->csum_start variable and move the content to can_skb_ext::can_gw_hops of the CAN skb extensions. The module parameter 'max_hops' has been reduced to a single byte to fit can_skb_ext::can_gw_hops as the maximum value to be stored is 6. Signed-off-by: Marc Kleine-Budde Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20260201-can_skb_ext-v8-6-3635d790fe8b@hartkopp.net Signed-off-by: Paolo Abeni --- drivers/net/can/vxcan.c | 2 +- net/can/gw.c | 23 ++++++----------------- 2 files changed, 7 insertions(+), 18 deletions(-) diff --git a/drivers/net/can/vxcan.c b/drivers/net/can/vxcan.c index ac2211f8070c..e882250180ef 100644 --- a/drivers/net/can/vxcan.c +++ b/drivers/net/can/vxcan.c @@ -77,7 +77,7 @@ static netdev_tx_t vxcan_xmit(struct sk_buff *oskb, struct net_device *dev) } /* reset CAN GW hop counter */ - skb->csum_start = 0; + csx->can_gw_hops = 0; skb->pkt_type = PACKET_BROADCAST; skb->dev = peer; skb->ip_summed = CHECKSUM_UNNECESSARY; diff --git a/net/can/gw.c b/net/can/gw.c index 816154a978c1..61a1e6b1b83f 100644 --- a/net/can/gw.c +++ b/net/can/gw.c @@ -71,8 +71,8 @@ MODULE_ALIAS(CAN_GW_NAME); #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, 0444); +static unsigned char max_hops __read_mostly = CGW_DEFAULT_HOPS; +module_param(max_hops, byte, 0444); MODULE_PARM_DESC(max_hops, "maximum " CAN_GW_NAME " routing hops for CAN frames " "(valid values: " __stringify(CGW_MIN_HOPS) "-" @@ -480,19 +480,8 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data) /* 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/unused 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) { + if (csx->can_gw_hops >= max_hops) { /* indicate deleted frames due to misconfiguration */ gwj->deleted_frames++; return; @@ -536,11 +525,11 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data) } /* put the incremented hop counter in the cloned skb */ - cgw_hops(nskb) = cgw_hops(skb) + 1; + ncsx->can_gw_hops = csx->can_gw_hops + 1; /* first processing of this CAN frame -> adjust to private hop limit */ - if (gwj->limit_hops && cgw_hops(nskb) == 1) - cgw_hops(nskb) = max_hops - gwj->limit_hops + 1; + if (gwj->limit_hops && ncsx->can_gw_hops == 1) + ncsx->can_gw_hops = max_hops - gwj->limit_hops + 1; nskb->dev = gwj->dst.dev; -- 2.47.3