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

[Wei Yang]

On Fri, Aug 09, 2019 at 01:50:24PM +0000, Schmid, Carsten wrote:
>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@xxxxxxxxxx>
>---
>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) {

In theory, child may have siblings. Would it be possible to have several
devices under xhci-hcd?

>+                               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

-- 
Wei Yang
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