linux-kernel - Re: [PATCHv2 net] bonding: fix missed rcu protection

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Message-ID: <YoRXjeCR2bbr5qzF@Laptop-X1>
Date:   Wed, 18 May 2022 10:18:53 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Jonathan Toppins <jtoppins@...hat.com>
Cc:     andy@...yhouse.net, davem@...emloft.net, dsahern@...il.com,
        eric.dumazet@...il.com, j.vosburgh@...il.com, kuba@...nel.org,
        netdev@...r.kernel.org, pabeni@...hat.com,
        syzbot+92beb3d46aab498710fa@...kaller.appspotmail.com,
        vfalico@...il.com, vladimir.oltean@....com,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 net] bonding: fix missed rcu protection

On Tue, May 17, 2022 at 01:32:58PM -0400, Jonathan Toppins wrote:
> Signed-off-by: Jonathan Toppins <jtoppins@...hat.com>
> ---
> RESEND, list still didn't receive my last version
> 
> The diffstat is slightly larger but IMO a slightly more readable version.
> When I was reading v2 I found myself jumping around.

Hi Jon,

Thanks for the commit. But..

> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 38e152548126..f9d27b63c454 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -5591,23 +5591,32 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
>  	const struct ethtool_ops *ops;
>  	struct net_device *real_dev;
>  	struct phy_device *phydev;
> +	int ret = 0;
>  
> +	rcu_read_lock();
>  	real_dev = bond_option_active_slave_get_rcu(bond);
> -	if (real_dev) {
> -		ops = real_dev->ethtool_ops;
> -		phydev = real_dev->phydev;
> -
> -		if (phy_has_tsinfo(phydev)) {
> -			return phy_ts_info(phydev, info);
> -		} else if (ops->get_ts_info) {
> -			return ops->get_ts_info(real_dev, info);
> -		}
> -	}
> +	if (real_dev)
> +		dev_hold(real_dev);
> +	rcu_read_unlock();
> +
> +	if (!real_dev)
> +		goto software;
>  
> +	ops = real_dev->ethtool_ops;
> +	phydev = real_dev->phydev;
> +
> +	if (phy_has_tsinfo(phydev))
> +		ret = phy_ts_info(phydev, info);
> +	else if (ops->get_ts_info)
> +		ret = ops->get_ts_info(real_dev, info);
	else {
		dev_put(real_dev);
		goto software;
	}

Here we need another check and goto software if !phy_has_tsinfo() and
no ops->get_ts_info. With this change we also have 2 goto and dev_put().

> +
> +	dev_put(real_dev);
> +	return ret;
> +
> +software:
>  	info->so_timestamping = SOF_TIMESTAMPING_RX_SOFTWARE |
>  				SOF_TIMESTAMPING_SOFTWARE;
>  	info->phc_index = -1;
> -
>  	return 0;
>  }

As Jakub remind, dev_hold() and dev_put() can take NULL now. So how about
this new patch:

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 38e152548126..b5c5196e03ee 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -5591,16 +5591,23 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
 	const struct ethtool_ops *ops;
 	struct net_device *real_dev;
 	struct phy_device *phydev;
+	int ret = 0;
 
+	rcu_read_lock();
 	real_dev = bond_option_active_slave_get_rcu(bond);
+	dev_hold(real_dev);
+	rcu_read_unlock();
+
 	if (real_dev) {
 		ops = real_dev->ethtool_ops;
 		phydev = real_dev->phydev;
 
 		if (phy_has_tsinfo(phydev)) {
-			return phy_ts_info(phydev, info);
+			ret = phy_ts_info(phydev, info);
+			goto out;
 		} else if (ops->get_ts_info) {
-			return ops->get_ts_info(real_dev, info);
+			ret = ops->get_ts_info(real_dev, info);
+			goto out;
 		}
 	}
 
@@ -5608,7 +5615,9 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
 				SOF_TIMESTAMPING_SOFTWARE;
 	info->phc_index = -1;
 
-	return 0;
+out:
+	dev_put(real_dev);
+	return ret;
 }

Thanks
Hangbin