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

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Date:   Fri, 14 Jul 2017 13:04:06 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, 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 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.

thanks,
neal