linux-kernel - Re: [PATCH] media: em28xx: Fix possible memory leak of em28xx struct

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Date:   Tue, 4 May 2021 16:07:27 -0300
From:   Igor Torrente <igormtorrente@...il.com>
To:     Shuah Khan <skhan@...uxfoundation.org>, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        hverkuil-cisco@...all.nl
Subject: Re: [PATCH] media: em28xx: Fix possible memory leak of em28xx struct



On 5/3/21 5:06 PM, Shuah Khan wrote:
> Hi Igor,
> 
> On 5/3/21 11:37 AM, Igor Matheus Andrade Torrente wrote:
>> The em28xx struct kref isn't being decreased after an error in the
>> em28xx_ir_init, leading to a possible memory leak.
>>
>> A kref_put is added to the error handler code.
>>
>> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@...il.com>
>> ---
>>   drivers/media/usb/em28xx/em28xx-input.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/media/usb/em28xx/em28xx-input.c 
>> b/drivers/media/usb/em28xx/em28xx-input.c
>> index 5aa15a7a49de..b89527014cad 100644
>> --- a/drivers/media/usb/em28xx/em28xx-input.c
>> +++ b/drivers/media/usb/em28xx/em28xx-input.c
>> @@ -720,7 +720,8 @@ static int em28xx_ir_init(struct em28xx *dev)
>>               dev->board.has_ir_i2c = 0;
>>               dev_warn(&dev->intf->dev,
>>                    "No i2c IR remote control device found.\n");
>> -            return -ENODEV;
>> +            err = -ENODEV;
>> +            goto ref_put;
> 
> This doesn't look right. em28xx_init_buttons() is already happened and
> em28xx_shutdown_buttons() needs to be done from fini. fini needs to run
> with this ref. If ref is released here, device might be released before
> em28xx_shutdown_buttons() can run leading to potential use-after-free
> 

Thanks for the feedback.

I sent a patch V2 that I think fix the problem pointed out.

>>           }
>>       }
>> @@ -735,7 +736,7 @@ static int em28xx_ir_init(struct em28xx *dev)
>>       ir = kzalloc(sizeof(*ir), GFP_KERNEL);
>>       if (!ir)
>> -        return -ENOMEM;
>> +        goto ref_put;
> 
> This doesn't look right. Same comment as above. fini accounts for null
> ir.
> 
>        em28xx_shutdown_buttons(dev);
> 
>         /* skip detach on non attached boards */
>         if (!ir)
>                 goto ref_put;
> 
> 
>>       rc = rc_allocate_device(RC_DRIVER_SCANCODE);
>>       if (!rc)
>>           goto error;
>> @@ -839,6 +840,8 @@ static int em28xx_ir_init(struct em28xx *dev)
>>       dev->ir = NULL;
>>       rc_free_device(rc);
>>       kfree(ir);
>> +ref_put:
>> +    kref_put(&dev->ref, em28xx_free_device);
>>       return err;
>>   }
>>
> 
> thanks,
> -- Shuah

Best regard,
---
Igor M. A. Torrente