[PATCH 4.19 083/120] net/sched: act_skbmod: Skip non-Ethernet packets

Greg Kroah-Hartman
2021-07-26T16:20:20Z

From: Peilin Ye <peilin.ye@bytedance.com>

[ Upstream commit 727d6a8b7ef3d25080fad228b2c4a1d4da5999c6 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/act_skbmod.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/sched/act_skbmod.c b/net/sched/act_skbmod.c
index 21d195296121..03a272af664a 100644
--- a/net/sched/act_skbmod.c
+++ b/net/sched/act_skbmod.c
@@ -10,6 +10,7 @@
*/

#include <linux/module.h>
+#include <linux/if_arp.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
@@ -36,6 +37,13 @@ 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
@@ -44,10 +52,6 @@ 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)
--
2.30.2