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

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Date:   Tue, 8 Jan 2019 17:28:05 +0100
From:   Tomas Bortoli <tomasbortoli@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, rkrcmar@...hat.com,
        kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, syzkaller@...glegroups.com
Subject: Re: [PATCH] KVM: validate userspace input in
 kvm_clear_dirty_log_protect()

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 ||
> 	    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 :)

Tomas