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

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Message-ID: <87ilokbx12.fsf@redhat.com>
Date:   Tue, 28 Jun 2022 17:58:01 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Schspa Shi <schspa@...il.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vfio: Clear the caps->buf to NULL after free

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>

>
> 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);
>>  	}