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

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Message-ID: <99de332c-d4e3-0628-8ad1-982032e67690@redhat.com>
Date:   Mon, 7 Jan 2019 23:42:20 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tomas Bortoli <tomasbortoli@...il.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()

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.

Paolo