linux-kernel - Re: [PATCH] ipv6: initialize treq->txhash in cookie_v6

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Date:   Fri, 14 Jul 2017 19:35:02 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv6: initialize treq->txhash in cookie_v6_check()

On Fri, Jul 14, 2017 at 7:04 PM, Neal Cardwell <ncardwell@...gle.com> wrote:
> On Fri, Jul 14, 2017 at 12:54 PM, Alexander Potapenko <glider@...gle.com> wrote:
>> KMSAN reported use of uninitialized memory in skb_set_hash_from_sk(),
>> which originated from the TCP request socket created in
>> cookie_v6_check():
> ...
>> --- a/net/ipv6/syncookies.c
>> +++ b/net/ipv6/syncookies.c
>> @@ -216,6 +216,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
>>         treq->rcv_isn = ntohl(th->seq) - 1;
>>         treq->snt_isn = cookie;
>>         treq->ts_off = 0;
>> +       treq->txhash = 0;
>>
>>         /*
>>          * We need to lookup the dst_entry to get the correct window size.
>
> I would have thought that the same fix is needed in the corresponding
> line in cookie_v4_check() in net/ipv4/syncookies.c? (I do not see
> txhash being initialized for the IPv4 side.) If it's not needed for
> some reason, then it would be worth a comment in the commit
> description to explain why not.
Most certainly it is needed. I haven't seen reports for that in the
wild and couldn't forge a repro triggering the bug in IPv4, but I'll
give it another shot.
> thanks,
> neal



-- 
Alexander Potapenko
Software Engineer

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