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    Subject[PATCH 5.10 090/167] net/sched: act_skbmod: Skip non-Ethernet packets
    Date
    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 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)
    --
    2.30.2


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