lkml.org 
[lkml]   [2020]   [Jul]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [net-next] seg6: using DSCP of inner IPv4 packets
From
Date
I will refactor the code of this function and submit a new patch.
Ahmed

On 31/07/2020 01:44, David Miller wrote:
> From: Ahmed Abdelsalam <ahabdels@gmail.com>
> Date: Tue, 28 Jul 2020 12:20:44 +0000
>
>> This patch allows copying the DSCP from inner IPv4 header to the
>> outer IPv6 header, when doing SRv6 Encapsulation.
>>
>> This allows forwarding packet across the SRv6 fabric based on their
>> original traffic class.
>>
>> Signed-off-by: Ahmed Abdelsalam <ahabdels@gmail.com>
>
> The conditionals in this function are now a mess.
>
>> - inner_hdr = ipv6_hdr(skb);
>> + if (skb->protocol == htons(ETH_P_IPV6))
>> + inner_hdr = ipv6_hdr(skb);
>> + else
>> + inner_ipv4_hdr = ip_hdr(skb);
>> +
>
> You assume that if skb->protocol is not ipv6 then it is ipv4.
>
>> @@ -138,6 +143,10 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
>> ip6_flow_hdr(hdr, ip6_tclass(ip6_flowinfo(inner_hdr)),
>> flowlabel);
>> hdr->hop_limit = inner_hdr->hop_limit;
>> + } else if (skb->protocol == htons(ETH_P_IP)) {
>> + ip6_flow_hdr(hdr, inner_ipv4_hdr->tos, flowlabel);
>> + hdr->hop_limit = inner_ipv4_hdr->ttl;
>> + memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
>> } else {
>> ip6_flow_hdr(hdr, 0, flowlabel);
>> hdr->hop_limit = ip6_dst_hoplimit(skb_dst(skb));
>
> But this code did not make that assumption at all.
>
> Only one of the two can be correct.
>
> The conditional assignment is also very ugly, you have two pointers
> conditionally initialized. The compiler is going to have a hard time
> figuring out that each pointer is only used in the code path where it
> is guaranteed to be initialiazed.
>
> And it can't do that, as far as the compiler knows, skb->protocol can
> change between those two locations. It MUST assume that can happen if
> there are any functions calls whatsoever between these two code points.
>
> This function has to be sanitized, with better handling of access to
> the inner protocol header values, before I am willing to apply this.
>

\
 
 \ /
  Last update: 2020-07-31 19:32    [W:0.057 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site