On Fri, 2014-02-14 at 17:35 +0000, Chris Wilson wrote:
> On Fri, Feb 14, 2014 at 07:23:32PM +0200, Imre Deak wrote:
> > pci_get_class(class, from) drops the refcount for 'from', so the
> > extra pci_dev_put we do on it will result in a use after free bug
> > sometime later starting with the WARN below.
>
> That's a very nice find.
>
> But you can tidy this loop up even more...
>
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > index 2d05d7c..4e4fc0c 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -347,7 +347,6 @@ void intel_detect_pch(struct drm_device *dev)
> > */
> > pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> > while (pch) {
>
> ...by noting that what you want here is
> while ((pch = pci_get_class(ISA<<8, pch)) {
>
> > - struct pci_dev *curr = pch;
> > if (pch->vendor == PCI_VENDOR_ID_INTEL) {
> > unsigned short id;
> > id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
> > @@ -385,15 +384,15 @@ void intel_detect_pch(struct drm_device *dev)
> > } else {
> > goto check_next;
> > }
> > - pci_dev_put(pch);
> > break;
> > }
> > check_next:
> > - pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
> > - pci_dev_put(curr);
> > + pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, pch);
> > }
> > if (!pch)
> > DRM_DEBUG_KMS("No PCH found?\n");
> > + else
> > + pci_dev_put(pch);
> > }
>
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 2d05d7c..9962aef 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -324,7 +324,7 @@ MODULE_DEVICE_TABLE(pci, pciidlist);
> void intel_detect_pch(struct drm_device *dev)
> {
> struct drm_i915_private *dev_priv = dev->dev_private;
> - struct pci_dev *pch;
> + struct pci_dev *pch = NULL;
>
> /* In all current cases, num_pipes is equivalent to the PCH_NOP setting
> * (which really amounts to a PCH but no South Display).
> @@ -345,12 +345,9 @@ void intel_detect_pch(struct drm_device *dev)
> * all the ISA bridge devices and check for the first match, instead
> * of only checking the first one.
> */
> - pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> - while (pch) {
> - struct pci_dev *curr = pch;
> + while ((pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, pch))) {
> if (pch->vendor == PCI_VENDOR_ID_INTEL) {
> - unsigned short id;
> - id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
> + unsigned short id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
> dev_priv->pch_id = id;
>
> if (id == INTEL_PCH_IBX_DEVICE_ID_TYPE) {
> @@ -382,18 +379,15 @@ void intel_detect_pch(struct drm_device *dev)
> DRM_DEBUG_KMS("Found LynxPoint LP PCH\n");
> WARN_ON(!IS_HASWELL(dev));
> WARN_ON(!IS_ULT(dev));
> - } else {
> - goto check_next;
> - }
> + } else
> + continue;
> +
> pci_dev_put(pch);
> break;
Yep, looks better. I would also move the pci_dev_put out of the loop and
remove the above continue. But it's fine for me either way.
--Imre
> }
> -check_next:
> - pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
> - pci_dev_put(curr);
> }
> if (!pch)
> - DRM_DEBUG_KMS("No PCH found?\n");
> + DRM_DEBUG_KMS("No PCH found.\n");
> }
>
>
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