From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51460) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XKBKa-0000Iz-9c for qemu-devel@nongnu.org; Wed, 20 Aug 2014 15:14:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XKBKU-0001N4-5H for qemu-devel@nongnu.org; Wed, 20 Aug 2014 15:14:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:13460) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XKBKT-0001MZ-TY for qemu-devel@nongnu.org; Wed, 20 Aug 2014 15:13:54 -0400 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s7KJDqC6004082 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Wed, 20 Aug 2014 15:13:53 -0400 Message-ID: <53F4F36D.8070905@redhat.com> Date: Wed, 20 Aug 2014 21:13:49 +0200 From: Max Reitz MIME-Version: 1.0 References: <1405117387-25539-1-git-send-email-mreitz@redhat.com> <1405117387-25539-2-git-send-email-mreitz@redhat.com> <20140820114059.GF6122@noname.redhat.com> In-Reply-To: <20140820114059.GF6122@noname.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/4] block: Correct bs->growable List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org, Stefan Hajnoczi , armbru@redhat.com On 20.08.2014 13:40, Kevin Wolf wrote: > Am 12.07.2014 um 00:23 hat Max Reitz geschrieben: >> Currently, the field "growable" in a BDS is set iff the BDS is opened in >> protocol mode (with O_BDRV_PROTOCOL). However, not every protocol block >> driver allows growing: NBD, for instance, does not. On the other hand, >> a non-protocol block driver may allow growing: The raw driver does. >> >> Fix this by correcting the "growable" field in the driver-specific open >> function for the BDS, if necessary. >> >> Signed-off-by: Max Reitz > I'm not sure I agree with bs->growable = true for raw. It's certainly > true that the backend can technically provide the functionality that > writes beyond EOF grow the file. That's not the point of bs->growable, > though. > > The point of it was to _forbid_ it to grow even when it's technically > possible (non-file protocols weren't really a thing back then, apart > from vvfat, so the assumption was that it's always technically > possible). growable was introduced with bdrv_check_request(), which is > supposed to reject guest requests after the end of the virtual disk (and > this fixed a CVE, see commit 71d0770c). You're now disabling this check > for raw. > > I think we need to make sure that bs->growable is only set if it is > opened for an image that has drv->requires_growing_file set and > therefore not directly used by a guest. > > Well, except that with node-name a guest will be able to use any image > in the chain... Might this mean that it's really a BlockBackend > property? I guess I can make things easy for me by just introducing some "really_growable" or "writes_beyond_eof" field or something for the sake of this series. ;-) Max