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envelope-from=darren.kenny@oracle.com; helo=mx0a-00069f02.pphosted.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Laurent Vivier , Thomas Huth , Prasad J Pandit , qemu-block@nongnu.org, John Snow , Markus Armbruster , Alexander Bulekov , Hanna Reitz , Paolo Bonzini , Gaoning Pan , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Philippe, A small nit below, but otherwise looks good. On Thursday, 2021-11-18 at 00:24:21 +01, Philippe Mathieu-Daud=C3=A9 wrote: > Guest might select another drive on the bus by setting the > DRIVE_SEL bit of the DIGITAL OUTPUT REGISTER (DOR). > The current controller model doesn't expect a BlockBackend > to be NULL. A simple way to fix CVE-2021-20196 is to create > an empty BlockBackend when it is missing. All further > accesses will be safely handled, and the controller state > machines keep behaving correctly. > > Fixes: CVE-2021-20196 > Reported-by: Gaoning Pan (Ant Security Light-Year Lab) > BugLink: https://bugs.launchpad.net/qemu/+bug/1912780 > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/338 > Signed-off-by: Philippe Mathieu-Daud=C3=A9 > --- > hw/block/fdc.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/hw/block/fdc.c b/hw/block/fdc.c > index fa933cd3263..eab17e946d6 100644 > --- a/hw/block/fdc.c > +++ b/hw/block/fdc.c > @@ -1161,7 +1161,19 @@ static FDrive *get_drv(FDCtrl *fdctrl, int unit) > =20 > static FDrive *get_cur_drv(FDCtrl *fdctrl) > { > - return get_drv(fdctrl, fdctrl->cur_drv); > + FDrive *cur_drv =3D get_drv(fdctrl, fdctrl->cur_drv); > + > + if (!cur_drv->blk) { > + /* > + * Kludge: empty drive line selected. Create an anonymous > + * BlockBackend to avoid NULL deref with various BlockBackend > + * API calls within this model (CVE-2021-20196). > + * Due to the controller QOM model limitations, we don't > + * attach the created to the controller. > The created .... to the controller Something is missing here, maybe 'device'? Thanks, Darren. > + */ > + cur_drv->blk =3D blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL= ); > + } > + return cur_drv; > } > =20 > /* Status A register : 0x00 (read-only) */ > --=20 > 2.31.1