linux-kernel - Re: [PATCH] misc: ocxl: fix possible double free in ocxl_file_register

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Date:   Tue, 19 Apr 2022 19:02:24 +0800
From:   Hangyu Hua <hbh25y@...il.com>
To:     Frederic Barrat <fbarrat@...ux.ibm.com>, ajd@...ux.ibm.com,
        arnd@...db.de, gregkh@...uxfoundation.org, mpe@...erman.id.au,
        alastair@...ilva.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc: ocxl: fix possible double free in
 ocxl_file_register_afu

On 2022/4/19 17:09, Frederic Barrat wrote:
> 
> 
> On 18/04/2022 10:57, Hangyu Hua wrote:
>> info_release() will be called in device_unregister() when info->dev's
>> reference count is 0. So there is no need to call ocxl_afu_put() and
>> kfree() again.
>>
>> Fix this by adding free_minor() and return to err_unregister error path.
>>
>> Fixes: 75ca758adbaf ("ocxl: Create a clear delineation between ocxl 
>> backend & frontend")
>> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
>> ---
> 
> 
> Thanks for fixing that error path!
> I'm now thinking it would be cleaner to have the call to free_minor() in 
> the info_release() callback but that would be another patch.
> In any case:
> Acked-by: Frederic Barrat <fbarrat@...ux.ibm.com>
> 
>    Fred
> 

I think it is a good idea to use callbacks to handle all garbage 
collections. And free_minor is used only in ocxl_file_register_afu() 
andocxl_file_unregister_afu(). So this should only require minor changes.

Thanks.

> 
>>   drivers/misc/ocxl/file.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/misc/ocxl/file.c b/drivers/misc/ocxl/file.c
>> index d881f5e40ad9..6777c419a8da 100644
>> --- a/drivers/misc/ocxl/file.c
>> +++ b/drivers/misc/ocxl/file.c
>> @@ -556,7 +556,9 @@ int ocxl_file_register_afu(struct ocxl_afu *afu)
>>   err_unregister:
>>       ocxl_sysfs_unregister_afu(info); // safe to call even if 
>> register failed
>> +    free_minor(info);
>>       device_unregister(&info->dev);
>> +    return rc;
>>   err_put:
>>       ocxl_afu_put(afu);
>>       free_minor(info);