linux-kernel - Re: [PATCH v2] vfio: Clear the caps->buf to NULL after free

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Date:   Wed, 29 Jun 2022 12:51:51 +0800
From:   Schspa Shi <schspa@...il.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vfio: Clear the caps->buf to NULL after free


Cornelia Huck <cohuck@...hat.com> writes:

> On Tue, Jun 28 2022, Alex Williamson 
> <alex.williamson@...hat.com> wrote:
>
>> On Tue, 28 Jun 2022 23:24:29 +0800
>> Schspa Shi <schspa@...il.com> wrote:
>>
>>> API vfio_info_cap_add will free caps->buf, clear it to NULL 
>>> after
>>> free.
>>
>> Should this be something like:
>>
>>     On buffer resize failure, vfio_info_cap_add() will free the 
>>     buffer,
>>     report zero for the size, and return -ENOMEM.  As 
>>     additional
>>     hardening, also clear the buffer pointer to prevent any 
>>     chance of a
>>     double free.
>
> I like that better. With that,
>
> Reviewed-by: Cornelia Huck <cohuck@...hat.com>
>

I have send a V3 patch for this comment change, please review it.

>>
>> Thanks,
>> Alex
>>  
>>> Signed-off-by: Schspa Shi <schspa@...il.com>
>>> ---
>>>  drivers/vfio/vfio.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>> 
>>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
>>> index 61e71c1154be..a0fb93866f61 100644
>>> --- a/drivers/vfio/vfio.c
>>> +++ b/drivers/vfio/vfio.c
>>> @@ -1812,6 +1812,7 @@ struct vfio_info_cap_header 
>>> *vfio_info_cap_add(struct vfio_info_cap *caps,
>>>  	buf = krealloc(caps->buf, caps->size + size, GFP_KERNEL);
>>>  	if (!buf) {
>>>  		kfree(caps->buf);
>>> +		caps->buf = NULL;
>>>  		caps->size = 0;
>>>  		return ERR_PTR(-ENOMEM);
>>>  	}

-- 
BRs
Schspa Shi