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Tue, 5 May 2020 09:16:25 +0000 (UTC) Date: Tue, 5 May 2020 11:16:24 +0200 From: Kevin Wolf To: Alberto Garcia Subject: Re: [PATCH v3] qcow2: Avoid integer wraparound in qcow2_co_truncate() Message-ID: <20200505091624.GE5759@linux.fritz.box> References: <20200504155217.10325-1-berto@igalia.com> <6fefd4af-3687-7f38-3933-aa67f2f221e8@redhat.com> <20200505085412.GD5759@linux.fritz.box> MIME-Version: 1.0 In-Reply-To: <20200505085412.GD5759@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/05 03:48:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 05.05.2020 um 10:54 hat Kevin Wolf geschrieben: > Am 04.05.2020 um 19:07 hat Alberto Garcia geschrieben: > > On Mon 04 May 2020 06:01:19 PM CEST, Eric Blake wrote: > > >> +_supported_fmt qcow2 > > >> +_supported_proto file > > > > > > Do we have to limit it to qcow2 and file? Yes, it's testing a bugfix > > > for qcow2, but are there other formats that it doesn't hurt to have > > > the extra testing? > >=20 > > It doesn't work with any other format at the moment (meaning: reading > > the tail of the image after growing it returns the data from the backin= g > > file). > >=20 > > Also, it seems that qemu-img's -F does not work with other formats > > either. > >=20 > > > Also, I don't see anything preventing this from working with non-file > > > protocol. > >=20 > > Right, that can be updated I guess (whoever commits this, feel free to > > do it). >=20 > I don't know for which protocols it works. I know that qcow2 over nbd > doesn't work. >=20 > But I think there is a more important problem with the test: It seems to > pass even with old binaries that don't have the fix. Is this only on my > system or do you get the same? Ah, I do get the overflow in the calculation of the length for qcow2_cluster_zeroize(), but size_to_clusters() inside the function overflows back the other direction, so this ends up with nb_clusters =3D 0 and we don't do anything bad. We could probably trigger a bad case with data_file_raw=3Don, but then we don't have a backing file, so nothing sets BDRV_REQ_ZERO_WRITE. So I guess the bug isn't even really testable, but we just add the test in case something else in the same scenario breaks? Kevin