netdev - Re: [PATCH v3] net: mdiobus: fix an OF node reference leak

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Message-ID: <06dcce52-5df2-4e78-9f7a-418c3e16e4db@pf.is.s.u-tokyo.ac.jp>
Date: Wed, 18 Dec 2024 12:54:06 +0900
From: Joe Hattori <joe@...is.s.u-tokyo.ac.jp>
To: Andrew Lunn <andrew@...n.ch>
Cc: hkallweit1@...il.com, linux@...linux.org.uk, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 netdev@...r.kernel.org
Subject: Re: [PATCH v3] net: mdiobus: fix an OF node reference leak

Thank you for your review.

On 12/16/24 18:33, Andrew Lunn wrote:
> On Mon, Dec 16, 2024 at 10:40:55AM +0900, Joe Hattori wrote:
>> fwnode_find_mii_timestamper() calls of_parse_phandle_with_fixed_args()
>> but does not decrement the refcount of the obtained OF node. Add an
>> of_node_put() call before returning from the function.
>>
>> This bug was detected by an experimental static analysis tool that I am
>> developing.
> 
> Just out of curiosity, have you improved this tool so it now reports
> the missing put you handled in version 3? I expect there is more code
> with the same error which a static analyser should be able to find
> when examining the abstract syntax tree.

Yes, and I am experimenting with other driver codes as well.

> 
>> +++ b/drivers/net/mdio/fwnode_mdio.c
>> @@ -41,6 +41,7 @@ static struct mii_timestamper *
>>   fwnode_find_mii_timestamper(struct fwnode_handle *fwnode)
>>   {
>>   	struct of_phandle_args arg;
>> +	struct mii_timestamper *mii_ts;
>>   	int err;
> 
> The netdev subsystem wants variables declared longest first, shortest
> last, also known as reverse Christmas tree. As you work in different
> parts of the tree, you will find each subsystem has its own set of
> rules you will need to learn.

TIL. Applied in the v4 patch.

>    
>>   	if (is_acpi_node(fwnode))
>> @@ -53,10 +54,14 @@ fwnode_find_mii_timestamper(struct fwnode_handle *fwnode)
>>   	else if (err)
>>   		return ERR_PTR(err);
>>   
>> -	if (arg.args_count != 1)
>> +	if (arg.args_count != 1) {
>> +		of_node_put(arg.np);
>>   		return ERR_PTR(-EINVAL);
>> +	}
>>   
>> -	return register_mii_timestamper(arg.np, arg.args[0]);
>> +	mii_ts = register_mii_timestamper(arg.np, arg.args[0]);
>> +	of_node_put(arg.np);
>> +	return mii_ts;
>>   }
> 
> Although this is correct, a more normal practice is to put all the
> cleanup at the end of the function and use a goto:
> 
> 	if (arg.args_count != 1) {
> 		mii_ts = ERR_PTR(-EINVAL);
> 		goto put_node;
> 	}
> 
> 	mii_ts = register_mii_timestamper(arg.np, arg.args[0]);
> 
> put_node:
>          of_node_put(arg.np);
> 	return mii_ts;
> }
> 
> This tends to be more scalable, especially when more cleanup is
> required.

Makes sense. Applied in the v4 patch as well.

> 
> 	Andrew

Best,
Joe