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SubjectRe: [PATCH net] net: sit: fix UBSAN Undefined behaviour in check_6rd
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From: David Miller <davem@davemloft.net>
Date: Mon, 11 Mar 2019 10:29:37 -0700 (PDT)

> From: linmiaohe <linmiaohe@huawei.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.

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