Re: [PATCH 1/2] pci: bounds check offsets into config_map

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 20, 2011 at 07:49:34PM -0400, Donald Dutile wrote:
> Bounds check to avoid walking off config_map[]
> and corrupting what is after it.
> 
> Signed-off-by: Donald Dutile <ddutile@redhat.com>
> cc: Alex Williamson <alex.williamson@redhat.com>
> cc: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
>  hw/pci.c |   16 ++++++++++++++--
>  1 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 5deaa04..9a7ff2d 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -2078,12 +2078,24 @@ int pci_add_capability(PCIDevice *pdev, uint8_t cap_id,
>          }
>      } else {
>          int i;
> +	uint32_t config_size = pci_config_size(pdev);

This is actually slightly wrong: even for express
devices, legacy capabilities can not spill out from
the low 256 bytes: the extended config space has its
own capability list always starting with the express
capability at offset 256.

> +
> +	/* ensure don't walk off end of config_map[] */
> +	if (offset > (config_size - size)) {

I prefer not to have () around math here.


> +            fprintf(stderr, "ERROR: %04x:%02x:%02x.%x "
> +                    "Attempt to add PCI capability 0x%x at offset 0x%x,"
> +                    "size 0x%x, which exceeds emulated PCI config space 0x%x\n",
> +                    pci_find_domain(pdev->bus), pci_bus_num(pdev->bus),
> +                    PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn),
> +                    cap_id, offset, size, config_size);
> +	    return -EINVAL;
> +	}
>  
>          for (i = offset; i < offset + size; i++) {
>              if (pdev->config_map[i]) {
>                  fprintf(stderr, "ERROR: %04x:%02x:%02x.%x "
> -                        "Attempt to add PCI capability %x at offset "
> -                        "%x overlaps existing capability %x at offset %x\n",
> +                        "Attempt to add PCI capability 0x%x at offset "
> +                        "0x%x overlaps existing capability 0x%x at offset 0x%x\n",
>                          pci_find_domain(pdev->bus), pci_bus_num(pdev->bus),
>                          PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn),
>                          cap_id, offset, pdev->config_map[i], i);