netdev - Re: [PATCH] ip6_gre: simplify gre header parsing in ip6gre

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Date:   Tue, 11 Sep 2018 10:19:31 +0800
From:   Haishuang Yan <yanhaishuang@...s.chinamobile.com>
To:     Jiri Benc <jbenc@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ip6_gre: simplify gre header parsing in ip6gre_err



> On 2018年9月10日, at 下午11:36, Jiri Benc <jbenc@...hat.com> wrote:
> 
> On Mon, 10 Sep 2018 16:25:09 +0800, Haishuang Yan wrote:
>> +	if (gre_parse_header(skb, &tpi, &csum_err, htons(ETH_P_IPV6),
>> +			     offset) < 0) {
>> +		if (!csum_err)		/* ignore csum errors. */
>> +			return;
>> 	}
> 
> gre_parse_header stops parsing when csum_err is encountered. Which
> means tpi.key is undefined...
> 
>> 
>> -	if (!pskb_may_pull(skb, offset + grehlen))
>> -		return;
>> 	ipv6h = (const struct ipv6hdr *)skb->data;
>> -	greh = (const struct gre_base_hdr *)(skb->data + offset);
>> -	key = key_off ? *(__be32 *)(skb->data + key_off) : 0;
>> -
>> 	t = ip6gre_tunnel_lookup(skb->dev, &ipv6h->daddr, &ipv6h->saddr,
>> -				 key, greh->protocol);
>> +				 tpi.key, tpi.proto);
> 
> ...and can't be used here.
> 
> Jiri
> 

You are right. Thanks for reviewing. So the same problem also arise in ipgre_err code:

   187         iph = (const struct iphdr *)(icmp_hdr(skb) + 1);
   188         t = ip_tunnel_lookup(itn, skb->dev->ifindex, tpi->flags,
   189                              iph->daddr, iph->saddr, tpi->key);

Since csum_err may not be used outside, how about refactoring gre_parse_header function like this:

--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,

        options = (__be32 *)(greh + 1);
        if (greh->flags & GRE_CSUM) {
-               if (skb_checksum_simple_validate(skb)) {
+               if (csum_err && skb_checksum_simple_validate(skb)) {
                        *csum_err = true;
                        return -EINVAL;
                }

And in gre_err function, we can call gre_parse_header(skb, &tpi, NULL, **) like this:

--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -234,11 +234,9 @@ static void gre_err(struct sk_buff *skb, u32 info)
        struct tnl_ptk_info tpi;
        bool csum_err = false;

-       if (gre_parse_header(skb, &tpi, &csum_err, htons(ETH_P_IP),
-                            iph->ihl * 4) < 0) {
-               if (!csum_err)          /* ignore csum errors. */
+       if (gre_parse_header(skb, &tpi, NULL, htons(ETH_P_IP),
+                            iph->ihl * 4) < 0)
                        return;
-       }