linux-kernel - Re: [PATCH 4.19 29/58] bonding: fix data-races around agg_select

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Message-ID: <20220222153528.GA27262@amd>
Date:   Tue, 22 Feb 2022 16:35:28 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        syzbot <syzkaller@...glegroups.com>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 4.19 29/58] bonding: fix data-races around
 agg_select_timer

Hi!

> syzbot reported that two threads might write over agg_select_timer
> at the same time. Make agg_select_timer atomic to fix the races.

Ok, but:

> --- a/drivers/net/bonding/bond_3ad.c
> +++ b/drivers/net/bonding/bond_3ad.c
> @@ -249,7 +249,7 @@ static inline int __check_agg_selection_
>  	if (bond == NULL)
>  		return 0;
>  
> -	return BOND_AD_INFO(bond).agg_select_timer ? 1 : 0;
> +	return atomic_read(&BOND_AD_INFO(bond).agg_select_timer) ? 1 : 0;
>  }

This could probably use !!.

> +static bool bond_agg_timer_advance(struct bonding *bond)
> +{
> +	int val, nval;
> +
> +	while (1) {
> +		val = atomic_read(&BOND_AD_INFO(bond).agg_select_timer);
> +		if (!val)
> +			return false;
> +		nval = val - 1;
> +		if (atomic_cmpxchg(&BOND_AD_INFO(bond).agg_select_timer,
> +				   val, nval) == val)
> +			break;
> +	}
> +	return nval == 0;
> +}

This should really be atomic_dec_if_positive, no?

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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