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

[Kevin Wolf <kwolf@redhat.com>]

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 <liq3ea@gmail.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Li Qiang <liq3ea@gmail.com>
> ---
>  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?

If this happens, we still have .max_access_size = 8. The next question is
then, is NVME_CMBSZ_GETSIZE guaranteed to be at least 8? I suppose yes,
but do we want to rely on this for security?

Kevin