From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37683) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gMcBD-0000wF-J7 for qemu-devel@nongnu.org; Tue, 13 Nov 2018 12:08:48 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gMcB9-00018y-8F for qemu-devel@nongnu.org; Tue, 13 Nov 2018 12:08:47 -0500 References: <20181113164544.9906-1-berto@igalia.com> From: Eric Blake Message-ID: Date: Tue, 13 Nov 2018 11:06:54 -0600 MIME-Version: 1.0 In-Reply-To: <20181113164544.9906-1-berto@igalia.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [for 3.1? PATCH] qcow2: Assert that refcount block offsets fit in the refcount table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alberto Garcia , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Kevin Wolf , Max Reitz On 11/13/18 10:45 AM, Alberto Garcia wrote: > Refcount table entries have a field to store the offset of the > refcount block. The rest of the bits of the entry are currently > reserved. > > The offset is always taken from the entry using REFT_OFFSET_MASK to > ensure that we only use the bits that belong to that field. > > While that mask is used every time we read from the refcount table, it > is never used when we write to it. Due to the other constraints of the > qcow2 format QEMU can never produce refcount block offsets that don't > fit in that field so any such offset when allocating a refcount block > would indicate a bug in QEMU. > --- > block/qcow2-refcount.c | 3 +++ > 1 file changed, 3 insertions(+) > Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org