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From:   Brian Vazquez <brianvv@google.com>
Date:   Wed, 26 Jan 2022 09:43:54 -0800
Message-ID: <CAMzD94QFnN013ePHb+yGYGFrFSWBDG-aLF8v=A2+kvj00YStmA@mail.gmail.com>
Subject: Re: [PATCH v4 net-next] net-core: add InMacErrors counter
To:     Jeffrey Ji <jeffreyjilinux@gmail.com>
Cc:     Eric Dumazet <edumazet@google.com>,
        "David S . Miller" <davem@davemloft.net>,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        jeffreyji <jeffreyji@google.com>
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Reviewed-by: Brian Vazquez <brianvv@google.com>

On Tue, Jan 25, 2022 at 3:24 PM Jeffrey Ji <jeffreyjilinux@gmail.com> wrote:
>
> From: jeffreyji <jeffreyji@google.com>
>
> Increment InMacErrors counter when packet dropped due to incorrect dest
> MAC addr.
>
> An example when this drop can occur is when manually crafting raw
> packets that will be consumed by a user space application via a tap
> device. For testing purposes local traffic was generated using trafgen
> for the client and netcat to start a server
>
> example output from nstat:
> \~# nstat -a | grep InMac
> Ip6InMacErrors                  0                  0.0
> IpExtInMacErrors                1                  0.0
>
> Tested: Created 2 netns, sent 1 packet using trafgen from 1 to the other
> with "{eth(daddr=$INCORRECT_MAC...}", verified that nstat showed the
> counter was incremented.
>
> Changelog:
>
> v3-4:
> Remove Change-Id
>
> v2:
> Use skb_free_reason() for tracing
> Add real-life example in patch msg
>
> Signed-off-by: jeffreyji <jeffreyji@google.com>
> ---
>  include/linux/skbuff.h    |  1 +
>  include/uapi/linux/snmp.h |  1 +
>  net/ipv4/ip_input.c       |  7 +++++--
>  net/ipv4/proc.c           |  1 +
>  net/ipv6/ip6_input.c      | 12 +++++++-----
>  net/ipv6/proc.c           |  1 +
>  6 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index bf11e1fbd69b..04a36352f677 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -320,6 +320,7 @@ enum skb_drop_reason {
>         SKB_DROP_REASON_TCP_CSUM,
>         SKB_DROP_REASON_TCP_FILTER,
>         SKB_DROP_REASON_UDP_CSUM,
> +       SKB_DROP_REASON_BAD_DEST_MAC,
>         SKB_DROP_REASON_MAX,
>  };
>
> diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
> index 904909d020e2..ac2fac12dd7d 100644
> --- a/include/uapi/linux/snmp.h
> +++ b/include/uapi/linux/snmp.h
> @@ -57,6 +57,7 @@ enum
>         IPSTATS_MIB_ECT0PKTS,                   /* InECT0Pkts */
>         IPSTATS_MIB_CEPKTS,                     /* InCEPkts */
>         IPSTATS_MIB_REASM_OVERLAPS,             /* ReasmOverlaps */
> +       IPSTATS_MIB_INMACERRORS,                /* InMacErrors */
>         __IPSTATS_MIB_MAX
>  };
>
> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> index 3a025c011971..379ef6b46920 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -441,8 +441,11 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
>         /* When the interface is in promisc. mode, drop all the crap
>          * that it receives, do not try to analyse it.
>          */
> -       if (skb->pkt_type == PACKET_OTHERHOST)
> -               goto drop;
> +       if (skb->pkt_type == PACKET_OTHERHOST) {
> +               __IP_INC_STATS(net, IPSTATS_MIB_INMACERRORS);
> +               kfree_skb_reason(skb, SKB_DROP_REASON_BAD_DEST_MAC);
> +               return NULL;
> +       }
>
>         __IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
>
> diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
> index f30273afb539..dfe0a1dbf8e9 100644
> --- a/net/ipv4/proc.c
> +++ b/net/ipv4/proc.c
> @@ -117,6 +117,7 @@ static const struct snmp_mib snmp4_ipextstats_list[] = {
>         SNMP_MIB_ITEM("InECT0Pkts", IPSTATS_MIB_ECT0PKTS),
>         SNMP_MIB_ITEM("InCEPkts", IPSTATS_MIB_CEPKTS),
>         SNMP_MIB_ITEM("ReasmOverlaps", IPSTATS_MIB_REASM_OVERLAPS),
> +       SNMP_MIB_ITEM("InMacErrors", IPSTATS_MIB_INMACERRORS),
>         SNMP_MIB_SENTINEL
>  };
>
> diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
> index 80256717868e..f6245fba7699 100644
> --- a/net/ipv6/ip6_input.c
> +++ b/net/ipv6/ip6_input.c
> @@ -149,15 +149,17 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff *skb, struct net_device *dev,
>         u32 pkt_len;
>         struct inet6_dev *idev;
>
> -       if (skb->pkt_type == PACKET_OTHERHOST) {
> -               kfree_skb(skb);
> -               return NULL;
> -       }
> -
>         rcu_read_lock();
>
>         idev = __in6_dev_get(skb->dev);
>
> +       if (skb->pkt_type == PACKET_OTHERHOST) {
> +               __IP6_INC_STATS(net, idev, IPSTATS_MIB_INMACERRORS);
> +               rcu_read_unlock();
> +               kfree_skb_reason(skb, SKB_DROP_REASON_BAD_DEST_MAC);
> +               return NULL;
> +       }
> +
>         __IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_IN, skb->len);
>
>         if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL ||
> diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
> index d6306aa46bb1..76e6119ba558 100644
> --- a/net/ipv6/proc.c
> +++ b/net/ipv6/proc.c
> @@ -84,6 +84,7 @@ static const struct snmp_mib snmp6_ipstats_list[] = {
>         SNMP_MIB_ITEM("Ip6InECT1Pkts", IPSTATS_MIB_ECT1PKTS),
>         SNMP_MIB_ITEM("Ip6InECT0Pkts", IPSTATS_MIB_ECT0PKTS),
>         SNMP_MIB_ITEM("Ip6InCEPkts", IPSTATS_MIB_CEPKTS),
> +       SNMP_MIB_ITEM("Ip6InMacErrors", IPSTATS_MIB_INMACERRORS),
>         SNMP_MIB_SENTINEL
>  };
>
> --
> 2.35.0.rc0.227.g00780c9af4-goog
>