diff options
| author | Philippe Mathieu-Daudé <philmd@redhat.com> | 2021-11-24 17:15:35 +0100 |
|---|---|---|
| committer | John Snow <jsnow@redhat.com> | 2021-12-02 01:09:38 -0500 |
| commit | 1ab95af033a419e7a64e2d58e67dd96b20af5233 (patch) | |
| tree | f06772abbb769e6a5718bb49befab7958944516f | |
| parent | b154791e7b6d4ca5cdcd54443484d97360bd7ad2 (diff) | |
hw/block/fdc: Kludge missing floppy drive to fix CVE-2021-20196
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.
Cc: qemu-stable@nongnu.org
Fixes: CVE-2021-20196
Reported-by: Gaoning Pan (Ant Security Light-Year Lab) <pgn@zju.edu.cn>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20211124161536.631563-3-philmd@redhat.com
BugLink: https://bugs.launchpad.net/qemu/+bug/1912780
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/338
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
| -rw-r--r-- | hw/block/fdc.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/hw/block/fdc.c b/hw/block/fdc.c index 1dbf3f6028..21d18ac2e3 100644 --- a/hw/block/fdc.c +++ b/hw/block/fdc.c @@ -1166,7 +1166,19 @@ 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 device. + */ + cur_drv->blk = blk_create_empty_drive(); + } + return cur_drv; } /* Status A register : 0x00 (read-only) */ |