net/sched: act_skbmod: Skip non-Ethernet packets

Currently tcf_skbmod_act() assumes that packets use Ethernet as their L2
protocol, which is not always the case.  As an example, for CAN devices:

	$ ip link add dev vcan0 type vcan
	$ ip link set up vcan0
	$ tc qdisc add dev vcan0 root handle 1: htb
	$ tc filter add dev vcan0 parent 1: protocol ip prio 10 \
		matchall action skbmod swap mac

Doing the above silently corrupts all the packets.  Do not perform skbmod
actions for non-Ethernet packets.

Fixes: 86da71b57383 ("net_sched: Introduce skbmod action")
Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/act_skbmod.c b/net/sched/act_skbmod.c
index 81a1c67335be62d04a468711c353efc90df9a26f..8d17a543cc9fef921dfba1bb5fe10a6d4494f63b 100644 (file)
--- a/net/sched/act_skbmod.c
+++ b/net/sched/act_skbmod.c
@@ -6,6 +6,7 @@
 */
 
 #include <linux/module.h>
+#include <linux/if_arp.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/skbuff.h>
@@ -33,6 +34,13 @@ static int tcf_skbmod_act(struct sk_buff *skb, const struct tc_action *a,
        tcf_lastuse_update(&d->tcf_tm);
        bstats_cpu_update(this_cpu_ptr(d->common.cpu_bstats), skb);
 
+       action = READ_ONCE(d->tcf_action);
+       if (unlikely(action == TC_ACT_SHOT))
+               goto drop;
+
+       if (!skb->dev || skb->dev->type != ARPHRD_ETHER)
+               return action;
+
        /* XXX: if you are going to edit more fields beyond ethernet header
         * (example when you add IP header replacement or vlan swap)
         * then MAX_EDIT_LEN needs to change appropriately
@@ -41,10 +49,6 @@ static int tcf_skbmod_act(struct sk_buff *skb, const struct tc_action *a,
        if (unlikely(err)) /* best policy is to drop on the floor */
                goto drop;
 
-       action = READ_ONCE(d->tcf_action);
-       if (unlikely(action == TC_ACT_SHOT))
-               goto drop;
-
        p = rcu_dereference_bh(d->skbmod_p);
        flags = p->flags;
        if (flags & SKBMOD_F_DMAC)