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 <[email protected]> --- 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. --- 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
