Re: [Qemu-devel] [PATCH] nvme: fix oob access issue(CVE-2018-16847)

[Li Qiang]

Kevin Wolf <address@hidden> 于2018年11月2日周五 下午11:42写道：

> Am 02.11.2018 um 16:22 hat Li Qiang geschrieben:
> > Hello Kevin,
> >
> > Kevin Wolf <address@hidden> 于2018年11月2日周五 下午6:54写道：
> >
> > > Am 02.11.2018 um 02:22 hat Li Qiang geschrieben:
> > > > Currently, the nvme_cmb_ops mr doesn't check the addr and size.
> > > > This can lead an oob access issue. This is triggerable in the guest.
> > > > Add check to avoid this issue.
> > > >
> > > > Fixes CVE-2018-16847.
> > > >
> > > > Reported-by: Li Qiang <address@hidden>
> > > > Reviewed-by: Paolo Bonzini <address@hidden>
> > > > Signed-off-by: Li Qiang <address@hidden>
> > > > ---
> > > >  hw/block/nvme.c | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > > > index fc7dacb..d097add 100644
> > > > --- a/hw/block/nvme.c
> > > > +++ b/hw/block/nvme.c
> > > > @@ -1175,6 +1175,10 @@ static void nvme_cmb_write(void *opaque,
> hwaddr
> > > addr, uint64_t data,
> > > >      unsigned size)
> > > >  {
> > > >      NvmeCtrl *n = (NvmeCtrl *)opaque;
> > > > +
> > > > +    if (addr + size > NVME_CMBSZ_GETSIZE(n->bar.cmbsz)) {
> > >
> > > What prevents a guest from moving the device to the end of the address
> > > space and causing an integer overflow in addr + size?
> > >
> > >
> > This can't happen as the addr can't be any value, it just can be in the
> > Memory Region n->ctrl_mem defines.
>
> Yes, but can't the guest map that memory region whereever it wants?
>
>
I think it can't happen, as the 'addr' here is the relative offset in the
MR.
As we don't (can't) register such a MMIO region(the end of this region is
very big to
make addr+size overflow, size here can only be 1,2, 4, 8,). So the 'addr'
here can't be that large.

Thanks,
Li Qiang


> (As Keith confirmed, the integer overflow doesn't seem to have any bad
> consequences here, but anyway.)
>
> Kevin
>