netdev - Re: [PATCH net 2/4] tcp: tcp_fragment() should apply sane memory limits

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Message-ID: <22211F2C-7381-4548-A3C6-E3AA097C9011@gmail.com>
Date:   Mon, 17 Jun 2019 10:14:55 -0700
From:   "Jonathan Lemon" <jonathan.lemon@...il.com>
To:     "Eric Dumazet" <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        "Eric Dumazet" <eric.dumazet@...il.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Jonathan Looney" <jtl@...flix.com>,
        "Neal Cardwell" <ncardwell@...gle.com>,
        "Tyler Hicks" <tyhicks@...onical.com>,
        "Yuchung Cheng" <ycheng@...gle.com>,
        "Bruce Curtis" <brucec@...flix.com>
Subject: Re: [PATCH net 2/4] tcp: tcp_fragment() should apply sane memory
 limits



On 17 Jun 2019, at 10:03, Eric Dumazet wrote:

> Jonathan Looney reported that a malicious peer can force a sender
> to fragment its retransmit queue into tiny skbs, inflating memory
> usage and/or overflow 32bit counters.
>
> TCP allows an application to queue up to sk_sndbuf bytes,
> so we need to give some allowance for non malicious splitting
> of retransmit queue.
>
> A new SNMP counter is added to monitor how many times TCP
> did not allow to split an skb if the allowance was exceeded.
>
> Note that this counter might increase in the case applications
> use SO_SNDBUF socket option to lower sk_sndbuf.
>
> CVE-2019-11478 : tcp_fragment, prevent fragmenting a packet when the
> 	socket is already using more than half the allowed space
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Jonathan Looney <jtl@...flix.com>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
> Reviewed-by: Tyler Hicks <tyhicks@...onical.com>
> Cc: Bruce Curtis <brucec@...flix.com>
> Cc: Jonathan Lemon <jonathan.lemon@...il.com>
Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>