On 10/8/20 10:30 AM, Hangbin Liu wrote:
> Hi Eric,
>
> Thanks for the comments. I should add "RFC" in subject next time for the
> uncertain fix patch.
>
> On Wed, Oct 07, 2020 at 11:35:41AM +0200, Eric Dumazet wrote:
>>
>>
>> On 10/7/20 5:55 AM, Hangbin Liu wrote:
>>
>>> kfree_skb(skb);
>>> @@ -282,6 +285,21 @@ static struct sk_buff *ip6_rcv_core(struct sk_buff
>>> *skb, struct net_device *dev,
>>> }
>>> }
>>>
>>> + /* RFC 8200, Section 4.5 Fragment Header:
>>> + * If the first fragment does not include all headers through an
>>> + * Upper-Layer header, then that fragment should be discarded and
>>> + * an ICMP Parameter Problem, Code 3, message should be sent to
>>> + * the source of the fragment, with the Pointer field set to zero.
>>> + */
>>> + nexthdr = hdr->nexthdr;
>>> + offset = ipv6_skip_exthdr(skb, skb_transport_offset(skb), &nexthdr,
>>> &frag_off);
>>> + if (frag_off == htons(IP6_MF) && !pskb_may_pull(skb, offset + 1)) {
>>> + __IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
>>> + icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
>>> + rcu_read_unlock();
>>> + return NULL;
>>> + }
>>> +
>>> rcu_read_unlock();
>>>
>>> /* Must drop socket now because of tproxy. */
>>>
>>
>> Ouch, this is quite a buggy patch.
>>
>> I doubt we want to add yet another ipv6_skip_exthdr() call in IPv6 fast path.
>>
>> Surely the presence of NEXTHDR_FRAGMENT is already tested elsewhere ?
>
> Would you like to help point where NEXTHDR_FRAGMENT was tested before IPv6
> defragment?
I think we have to ask the question : Should routers enforce the rule, or
only end points ?
End points must handle NEXTHDR_FRAGMENT, in ipv6_frag_rcv()
>
>>
>> Also, ipv6_skip_exthdr() does not pull anything in skb->head, it would be
>> strange
>> to force a pull of hundreds of bytes just because you want to check if an
>> extra byte is there,
>> if the packet could be forwarded as is, without additional memory
>> allocations.
>>
>> Testing skb->len should be more than enough at this stage.
>
> Ah, yes, I shouldn't call pskb_may_pull here.
>>
>> Also ipv6_skip_exthdr() can return an error.
>
> it returns -1 as error, If we tested it by (offset + 1 > skb->len), does
> that count as an error handler?
If there is an error, then you want to send the ICMP, right ?
The (offset + 1) expression will become 0, and surely the test will be false,
so you wont send the ICMP...
>
> Thanks
> Hangbin
>
