netdev - Re: [PATCH net-next] net: udp Allow CHECKSUM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 29 Jan 2019 14:04:40 +0800
From:   maowenan <maowenan@...wei.com>
To:     Tom Herbert <tom@...bertland.com>
CC:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] net: udp Allow CHECKSUM_UNNECESSARY packets to
 do GRO.



On 2019/1/29 12:01, Tom Herbert wrote:
> On Mon, Jan 28, 2019 at 7:00 PM maowenan <maowenan@...wei.com> wrote:
>>
>> Hi all，
>> Do you have any comments about this change?
>>
>>
>> On 2019/1/23 11:33, Mao Wenan wrote:
>>> When udp4_gro_receive() get one packet that uh->check=0,
>>> skb_gro_checksum_validate_zero_check() will set the
>>> skb->ip_summed = CHECKSUM_UNNECESSARY;
>>> skb->csum_level = 0;
>>> Then udp_gro_receive() will flush the packet which is not CHECKSUM_PARTIAL,
>>> It is not our expect,  because check=0 in udp header indicates this
>>> packet is no need to caculate checksum, we should go further to do GRO.
>>>
>>> This patch changes the value of csum_cnt according to skb->csum_level.
>>> ---
>>>  include/linux/netdevice.h | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>>> index 1377d08..9c819f1 100644
>>> --- a/include/linux/netdevice.h
>>> +++ b/include/linux/netdevice.h
>>> @@ -2764,6 +2764,7 @@ static inline void skb_gro_incr_csum_unnecessary(struct sk_buff *skb)
>>>                * during GRO. This saves work if we fallback to normal path.
>>>                */
>>>               __skb_incr_checksum_unnecessary(skb);
>>> +             NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1;
> 
> That doesn't look right. This would be reinitializing the GRO
> checksums from the beginning.
> 
>>>       }
>>>  }
>>>
>>>
>>
> I assume the code is bailing on this conditional:
> 
> if (NAPI_GRO_CB(skb)->encap_mark ||
>             (skb->ip_summed != CHECKSUM_PARTIAL &&
>              NAPI_GRO_CB(skb)->csum_cnt == 0 &&
>              !NAPI_GRO_CB(skb)->csum_valid) ||
>             !udp_sk(sk)->gro_receive)
>                 goto out_unlock;
> 
> I am trying to remember why this needs to check csum_cnt. If there was
> a csum_cnt for the UDP csum being zero from checksum-unnecessary, it
> was consumed by skb_gro_checksum_validate_zero_check in UDP4 GRO
> received.

We have met the scene about two VMs in different host with vxlan packets, when udp4_gro_receive receives
one packet with ip_summed=CHECKSUM_NONE,csum_cnt=0,csum_valid=0,and udp->check=0, then skb_gro_checksum_validate_zero_check()->
skb_gro_incr_csum_unnecessary() validate it and set ip_summed=CHECKSUM_UNNECESSARY,csum_level=0, but csum_cnt and csum_valid
keep zero value. Then it will be flushed in udp_gro_receive(), the codes as you have showed.

so I think it forgets to modify csum_cnt since csum_level is changed in skb_gro_incr_csum_unnecessary()->__skb_incr_checksum_unnecessary().

> 
> .
>