2021-07-20 02:35:23

by Peilin Ye

Subject: [PATCH net] net/sched: act_skbmod: Skip non-Ethernet packets

From: Peilin Ye <[email protected]>

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 <[email protected]>
Signed-off-by: Peilin Ye <[email protected]>
---
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 81a1c67335be..8d17a543cc9f 100644
--- 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)
--
2.20.1

2021-07-20 14:36:15

by patchwork-bot+netdevbpf

Subject: Re: [PATCH net] net/sched: act_skbmod: Skip non-Ethernet packets

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Mon, 19 Jul 2021 16:41:24 -0700 you wrote:
> From: Peilin Ye <[email protected]>
>
> 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
>
> [...]

Here is the summary with links:
- [net] net/sched: act_skbmod: Skip non-Ethernet packets
https://git.kernel.org/netdev/net/c/727d6a8b7ef3

You are awesome, thank you!
--
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