netdev - Re: [PATCH net] pkt_sched: fq: do not accept silly TCA_FQ

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Message-Id: <20200108.124137.101510987796630147.davem@davemloft.net>
Date:   Wed, 08 Jan 2020 12:41:37 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, fw@...len.de,
        syzbot+dc9071cc5a85950bdfce@...kaller.appspotmail.com
Subject: Re: [PATCH net] pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM

From: Eric Dumazet <edumazet@...gle.com>
Date: Mon,  6 Jan 2020 06:10:39 -0800

> As diagnosed by Florian :
> 
> If TCA_FQ_QUANTUM is set to 0x80000000, fq_deueue()
> can loop forever in :
> 
> if (f->credit <= 0) {
>   f->credit += q->quantum;
>   goto begin;
> }
> 
> ... because f->credit is either 0 or -2147483648.
> 
> Let's limit TCA_FQ_QUANTUM to no more than 1 << 20 :
> This max value should limit risks of breaking user setups
> while fixing this bug.
> 
> Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Diagnosed-by: Florian Westphal <fw@...len.de>
> Reported-by: syzbot+dc9071cc5a85950bdfce@...kaller.appspotmail.com

Applied and queued up for -stable, thanks.