On 11/18/21 11:44, Darren Kenny wrote: > Hi Philippe, > > A small nit below, but otherwise looks good. > > On Thursday, 2021-11-18 at 00:24:21 +01, Philippe Mathieu-Daudé 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) <p...@zju.edu.cn> >> BugLink: https://bugs.launchpad.net/qemu/+bug/1912780 >> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/338 >> Signed-off-by: Philippe Mathieu-Daudé <phi...@redhat.com> >> --- >> 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) >> >> static FDrive *get_cur_drv(FDCtrl *fdctrl) >> { >> - return get_drv(fdctrl, fdctrl->cur_drv); >> + FDrive *cur_drv = 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'?
OK. I forgot to add Cc: qemu-sta...@nongnu.org so will respin. Thanks, Phil.
