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

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Date:   Fri, 11 Jan 2019 14:49:56 +0100
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Tomas Bortoli <tomasbortoli@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, 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()

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->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.