Resend [PATCH] kernel/resource.c: invalidate parent when freed resource has childs

["Schmid, Carsten" <Carsten_Schmid@mentor.com>]

When a resource is freed and has children, the childrens are
left without any hint that their parent is no more valid.
This caused at least one use-after-free in the xhci-hcd using
ext-caps driver when platform code released platform devices.

Fix this by setting child's parent to zero and warn.

Signed-off-by: Carsten Schmid <carsten_schmid@mentor.com>
---
Rationale:
When hunting for the root cause of a crash on a 4.14.86 kernel, i
have found the root cause and checked it being still present
upstream. Our case:
Having xhci-hcd and intel_xhci_usb_sw active we can see in
/proc/meminfo: (exceirpt)
  b3c00000-b3c0ffff : 0000:00:15.0
    b3c00000-b3c0ffff : xhci-hcd
      b3c08070-b3c0846f : intel_xhci_usb_sw
intel_xhci_usb_sw being a child of xhci-hcd.

Doing an unbind command
echo 0000:00:15.0 > /sys/bus/pci/drivers/xhci_hcd/unbind
leads to xhci-hcd being freed in __release_region.
The intel_xhci_usb_sw resource is accessed in platform code
in platform_device_del with
                for (i = 0; i < pdev->num_resources; i++) {
                        struct resource *r = &pdev->resource[i];
                        if (r->parent)
                                release_resource(r);
                }
as the resource's parent has not been updated, the release_resource
uses the parent:
        p = &old->parent->child;
which is now invalid.
Fix this by marking the parent invalid in the child and give a warning
in dmesg.
---
Advised by Greg (thanks):
Try resending it with at least the people who get_maintainer.pl says has
touched that file last in it. [CS:done]

Also, Linus is the unofficial resource.c maintainer.  I think he has a
set of userspace testing scripts for changes somewhere, so you should
 cc: him too.  And might as well add me :) [CS:done]

 thanks,

 greg k-h
---
 kernel/resource.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/resource.c b/kernel/resource.c
index 158f04ec1d4f..95340cb0b1c2 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1200,6 +1200,15 @@ void __release_region(struct resource *parent, resource_size_t start,
                        write_unlock(&resource_lock);
                        if (res->flags & IORESOURCE_MUXED)
                                wake_up(&muxed_resource_wait);
+
+                       write_lock(&resource_lock);
+                       if (res->child) {
+                               printk(KERN_WARNING "__release_region: %s has child %s,"
+                                               "invalidating childs parent\n",
+                                               res->name, res->child->name);
+                               res->child->parent = NULL;
+                       }
+                       write_unlock(&resource_lock);
                        free_resource(res);
                        return;
                }
--
2.17.1