From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55414) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVyLM-0005nv-Uw for qemu-devel@nongnu.org; Fri, 14 Jul 2017 07:01:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVyLG-0002Yz-Uy for qemu-devel@nongnu.org; Fri, 14 Jul 2017 07:01:09 -0400 Date: Fri, 14 Jul 2017 12:00:48 +0100 From: "Daniel P. Berrange" Message-ID: <20170714110048.GC28095@redhat.com> Reply-To: "Daniel P. Berrange" MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Subject: [Qemu-devel] qcow2 not cleaning up during image create failure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, qemu-block@nongnu.org Cc: Kevin Wolf I've just been looking at the qcow2 image creation code, and found that if any method in qcow2_create2() returns an error, then we'll report that, but leave the newly created image file on disk in some partially initialized state. A user may unwittingly use this file later with undefined behaviour. This is particularly bad if we fail to setup encryption, because the user is left with a file with no encryption enabled. So I'm wondering how is the best way to clean up after failure ? Naively I would like to just unlink(filename), but IIUC, filename is not guaranteed to refer to a local file, and AFAIK, there is not bdrv_delete() method todo this portably. If we can't delete a file (because its a block device or network volume), then we must at least blank out the just-written qcow2 header with zeros. Ideas / suggestions. You can demo this easily, by adding ret = -EINVAL; immediately after the first blk_pwrite() call in qcow2_create2() diff --git a/block/qcow2.c b/block/qcow2.c index 75d3e3c731..205c924f6d 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2778,6 +2778,7 @@ static int qcow2_create2(const char *filename, int64_t total_size, ret = blk_pwrite(blk, 0, header, cluster_size, 0); g_free(header); + ret = -EINVAL; if (ret < 0) { error_setg_errno(errp, -ret, "Could not write qcow2 header"); goto out; $ qemu-img create -f qcow2 eek.img 1g Formatting 'eek.img', fmt=qcow2 size=1073741824 cluster_size=65536 lazy_refcounts=off refcount_bits=16 qemu-img: eek.img: Could not write qcow2 header: Invalid argument $ qemu-img info eek.img image: eek.img file format: qcow2 virtual size: 0 (0 bytes) disk size: 64K cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false I imagine this may well affect other disk format drivers too. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|