linux-kernel - Re: [PATCH] KVM: validate userspace input in kvm_clear_dirty_log

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Date:   Mon, 14 Jan 2019 10:10:45 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        Tomas Bortoli <tomasbortoli@...il.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com
Subject: Re: [PATCH] KVM: validate userspace input in
 kvm_clear_dirty_log_protect()

On 11/01/19 14:49, Radim Krčmář wrote:
> 2019-01-08 17:28+0100, Tomas Bortoli:
>> Hi Paolo,
>>
>> On 1/7/19 11:42 PM, Paolo Bonzini wrote:
>>> On 02/01/19 18:29, Tomas Bortoli wrote:
>>>>  	n = kvm_dirty_bitmap_bytes(memslot);
>>>> +
>>>> +	if (n << 3 < log->num_pages || log->first_page > log->num_pages)
>>>> +		return -EINVAL;
>>>> +
>>>
>>> This should be
>>>
>>> 	if (log->first_page > memslot->npages ||
> 
> (Wouldn't this be clearer with a >= instead?)

log->first_page == memslot->npages is technically okay if log->num_pages
is zero.

Paolo

>>> 	    log->num_pages > memslot->npages - log->first_page)
>>> 		return -EINVAL;
>>>
>>> i.e. the comparison should check the last page in the range, not the
>>> number of pages.  In addition, using "n" is unnecessary since we do have
>>> the memslot.  I'll do the changes myself if you prefer, but an ack would
>>> be nice.
>>>
>>>
>>
>>
>> Yeah, I agree. Thanks for the reply and sure you can do the changes, np :)
> 
> Done that and applied, thanks.
>