Re: [PULL 1/3] vfio/pci: add support for VF token

[Peter Maydell]

On Tue, 9 May 2023 at 23:01, Alex Williamson <alex.williamson@redhat.com> wrote:
>
> From: Minwoo Im <minwoo.im@samsung.com>
>
> VF token was introduced [1] to kernel vfio-pci along with SR-IOV
> support [2].  This patch adds support VF token among PF and VF(s). To
> passthu PCIe VF to a VM, kernel >= v5.7 needs this.
>
> It can be configured with UUID like:
>
>   -device vfio-pci,host=DDDD:BB:DD:F,vf-token=<uuid>,...
>
> [1] 
> https://lore.kernel.org/linux-pci/158396393244.5601.10297430724964025753.stgit@gimli.home/
> [2] 
> https://lore.kernel.org/linux-pci/158396044753.5601.14804870681174789709.stgit@gimli.home/
>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Minwoo Im <minwoo.im@samsung.com>
> Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
> Link: 
> https://lore.kernel.org/r/20230320073522epcms2p48f682ecdb73e0ae1a4850ad0712fd780@epcms2p4
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Hi; Coverity points out that this change introduces a buffer
overrun (CID 1522913). I dunno why it's taken it so long
to notice...

> ---
>  hw/vfio/pci.c | 13 ++++++++++++-
>  hw/vfio/pci.h |  1 +
>  2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index ec9a854361ac..cf27f28936cb 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -2856,6 +2856,8 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>      int groupid;
>      int i, ret;
>      bool is_mdev;
> +    char uuid[UUID_FMT_LEN];

We define the array uuid[] as UUID_FMT_LEN bytes long...

> +    char *name;
>
>      if (!vbasedev->sysfsdev) {
>          if (!(~vdev->host.domain || ~vdev->host.bus ||
> @@ -2936,7 +2938,15 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>          goto error;
>      }
>
> -    ret = vfio_get_device(group, vbasedev->name, vbasedev, errp);
> +    if (!qemu_uuid_is_null(&vdev->vf_token)) {
> +        qemu_uuid_unparse(&vdev->vf_token, uuid);

...but qemu_uuid_unparse() writes UUID_FMT_LEN + 1 bytes,
including a trailing NUL.

Every other use of UUID_FMT_LEN to declare an array
uses "UUID_FMT_LEN + 1" to avoid this.

(In fact, every use of UUID_FMT_LEN at all uses "+ 1",
which suggests that perhaps defining it differently (and
perhaps with a different name) would reduce the risk of
this particular bug...)

thanks
-- PMM