Re: [PATCH net] net: sit: fix UBSAN Undefined behaviour in check_6rd

[linmiaohe]

That's very nice of you. Thank you very much.

On 2019/3/12 1:30, David Miller wrote:
> From: David Miller <davem@xxxxxxxxxxxxx>
> Date: Mon, 11 Mar 2019 10:29:37 -0700 (PDT)
> 
>> From: linmiaohe <linmiaohe@xxxxxxxxxx>
>> Date: Mon, 11 Mar 2019 16:29:32 +0800
>>
>>> @@ -778,8 +778,9 @@ static bool check_6rd(struct ip_tunnel *tunnel, const struct in6_addr *v6dst,
>>>  		pbw0 = tunnel->ip6rd.prefixlen >> 5;
>>>  		pbi0 = tunnel->ip6rd.prefixlen & 0x1f;
>>>
>>> -		d = (ntohl(v6dst->s6_addr32[pbw0]) << pbi0) >>
>>> -		    tunnel->ip6rd.relay_prefixlen;
>>> +		d = tunnel->ip6rd.relay_prefixlen < 32 ?
>>> +			(ntohl(v6dst->s6_addr32[pbw0]) << pbi0) >>
>>> +		    tunnel->ip6rd.relay_prefixlen : 0;
>>>
>>
>> I hate the fact that we have to guard against something which the rest
>> of the code makes sure NEVER EVER happens.
>>
>> Every assignment of ->relay_prefixlen is guarded by a check against 32.
> 
> Sorry, I now understand, it can equal 32.
> 
> I'll apply this, thank you.
> 
> .
>