linux-kernel - Re: [PATCH net-next v12 12/13] net: ethtool: tsinfo: Add support for hwtstamp provider and get/set hwtstamp config

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Date: Fri, 17 May 2024 17:12:54 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Simon Horman <horms@...nel.org>
Cc: Florian Fainelli <florian.fainelli@...adcom.com>, Broadcom internal
 kernel review list <bcm-kernel-feedback-list@...adcom.com>, Andrew Lunn
 <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Richard Cochran <richardcochran@...il.com>, Radu
 Pirea <radu-nicolae.pirea@....nxp.com>, Jay Vosburgh
 <j.vosburgh@...il.com>, Andy Gospodarek <andy@...yhouse.net>, Nicolas Ferre
 <nicolas.ferre@...rochip.com>, Claudiu Beznea <claudiu.beznea@...on.dev>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, Jonathan Corbet
 <corbet@....net>, Horatiu Vultur <horatiu.vultur@...rochip.com>,
 UNGLinuxDriver@...rochip.com, Vladimir Oltean <vladimir.oltean@....com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, Maxime Chevallier
 <maxime.chevallier@...tlin.com>, Rahul Rameshbabu <rrameshbabu@...dia.com>
Subject: Re: [PATCH net-next v12 12/13] net: ethtool: tsinfo: Add support
 for hwtstamp provider and get/set hwtstamp config

On Sat, 4 May 2024 11:33:05 +0100
Simon Horman <horms@...nel.org> wrote:

> Hi Kory,
> 
> A few lines beyond this hunk, within the "if (hwtstamp)" block,
> is the following:
> 
> 		cfg->qualifier = dev->hwtstamp->qualifier;
> 
> Now that dev->hwtstamp is managed using RCU, I don't think it is correct
> to dereference it directly like this. Rather, the hwtstamp local variable,
> which has rcu_dereference'd this pointer should be used:
> 
> 		 cfg->qualifier = hwtstamp->qualifier;
> 
> Flagged by Sparse.

Yes indeed, thanks for the report.

> 
> ...
> 
> > diff --git a/net/ethtool/tsinfo.c b/net/ethtool/tsinfo.c  
> 
> ...
> 
> > +static int ethnl_tsinfo_dump_one_dev(struct sk_buff *skb, struct
> > net_device *dev,
> > +				     struct netlink_callback *cb)
> > +{
> > +	struct ethnl_tsinfo_dump_ctx *ctx = (void *)cb->ctx;
> > +	struct ptp_clock *ptp;
> > +	int ret;
> > +
> > +	netdev_for_each_ptp_clock_start(dev, ctx->pos_phcindex, ptp,
> > +					ctx->pos_phcindex) {
> > +		ret = ethnl_tsinfo_dump_one_ptp(skb, dev, cb, ptp);
> > +		if (ret < 0 && ret != -EOPNOTSUPP)
> > +			break;
> > +		ctx->pos_phcqualifier =
> > HWTSTAMP_PROVIDER_QUALIFIER_PRECISE;
> > +	}
> > +
> > +	return ret;  
> 
> Perhaps it is not possible, but if the loop iterates zero times then
> ret will be used uninitialised here.

Yes thanks!

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com