linux-kernel - Re: [PATCH] powerpc: kernel: fix a refcount leak in format

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Message-ID: <825f5cba-a62b-a691-225e-22f6bb9b10a8@linux.ibm.com>
Date:   Tue, 1 Mar 2022 11:50:13 -0800
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Hangyu Hua <hbh25y@...il.com>, benh@...nel.crashing.org,
        paulus@...ba.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: kernel: fix a refcount leak in format_show()

On 3/1/22 04:55, Michael Ellerman wrote:
> Hangyu Hua <hbh25y@...il.com> writes:
>> node needs to be dropped when of_property_read_string fails. So an earlier call
>> to of_node_put is required here.
> 
> That's true but ...
> 
>> diff --git a/arch/powerpc/kernel/secvar-sysfs.c b/arch/powerpc/kernel/secvar-sysfs.c
>> index a0a78aba2083..cd0fa7028d86 100644
>> --- a/arch/powerpc/kernel/secvar-sysfs.c
>> +++ b/arch/powerpc/kernel/secvar-sysfs.c
>> @@ -30,13 +30,12 @@ static ssize_t format_show(struct kobject *kobj, struct kobj_attribute *attr,
>>  		return -ENODEV;
> 
> There's also a reference leak there ^
> 
> So if you're going to touch this code I'd like you to fix both reference
> leaks in a single patch please.
> 
> Having the error cases set rc and then goto "out" which does the
> of_node_put() is the obvious solution I think.

update_kobj_size() in the same source file provides a good example of the
suggested solution.

-Tyrel

> 
> cheers
> 
>>  	rc = of_property_read_string(node, "format", &format);
>> +	of_node_put(node);
>>  	if (rc)
>>  		return rc;
>>  
>>  	rc = sprintf(buf, "%s\n", format);
>>  
>> -	of_node_put(node);
>> -
>>  	return rc;
>>  }
>>  
>> -- 
>> 2.25.1