netdev - Re: [PATCH net] net: sit: fix UBSAN Undefined behaviour in check

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Message-ID: <09b205d5-c22c-377c-31af-effc68884098@huawei.com>
Date:   Tue, 12 Mar 2019 14:01:01 +0800
From:   linmiaohe <linmiaohe@...wei.com>
To:     David Miller <davem@...emloft.net>
CC:     <kuznet@....inr.ac.ru>, <yoshfuji@...ux-ipv6.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <mingfangsen@...wei.com>
Subject: Re: [PATCH net] net: sit: fix UBSAN Undefined behaviour in check_6rd

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

On 2019/3/12 1:30, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Mon, 11 Mar 2019 10:29:37 -0700 (PDT)
> 
>> From: linmiaohe <linmiaohe@...wei.com>
>> 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.
> 
> .
>