On Tue, Feb 1, 2022 at 2:06 AM David Ahern <dsahern@xxxxxxxxx> wrote:
>
> On 1/28/22 12:33 AM, menglong8.dong@xxxxxxxxx wrote:
> \> diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> > index 3a025c011971..627fad437593 100644
> > --- a/net/ipv4/ip_input.c
> > +++ b/net/ipv4/ip_input.c
> > @@ -436,13 +436,18 @@ static int ip_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
> > static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
> > {
> > const struct iphdr *iph;
> > + int drop_reason;
> > u32 len;
> >
> > + drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
>
> move this line down, right before:
>
> if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> goto inhdr_error;
>
> > +
> > /* 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)
> > + if (skb->pkt_type == PACKET_OTHERHOST) {
> > + drop_reason = SKB_DROP_REASON_OTHERHOST;
> > goto drop;
> > + }
> >
> > __IP_UPD_PO_STATS(net, IPSTATS_MIB_IN, skb->len);
> >
> > @@ -488,6 +493,7 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
> >
> > len = ntohs(iph->tot_len);
> > if (skb->len < len) {
> > + drop_reason = SKB_DROP_REASON_PKT_TOO_SMALL;
> > __IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
> > goto drop;
> > } else if (len < (iph->ihl*4))
> > @@ -516,11 +522,13 @@ static struct sk_buff *ip_rcv_core(struct sk_buff *skb, struct net *net)
> > return skb;
> >
> > csum_error:
> > + drop_reason = SKB_DROP_REASON_IP_CSUM;
> > __IP_INC_STATS(net, IPSTATS_MIB_CSUMERRORS);
> > inhdr_error:
> > + drop_reason = drop_reason ?: SKB_DROP_REASON_IP_INHDR;
>
> That makes assumptions about the value of SKB_DROP_REASON_NOT_SPECIFIED.
> Make that line:
> if (drop_reason != SKB_DROP_REASON_NOT_SPECIFIED)
> drop_reason = SKB_DROP_REASON_IP_INHDR;
>
You are right, the assumptions here are unsuitable. But I guess it
should be this?
if (drop_reason == SKB_DROP_REASON_NOT_SPECIFIED)
drop_reason = SKB_DROP_REASON_IP_INHDR;
> > __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
> > drop:
> > - kfree_skb(skb);
> > + kfree_skb_reason(skb, drop_reason);
> > out:
> > return NULL;
> > }
>
