[PATCH v2] 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.

In such case, warn and release all resources beyond.

Signed-off-by: Carsten Schmid <carsten_schmid@mentor.com>
---
v2:
- release everything below the released resource, not only
  one child; re-using __release_child_resources
  (Inspired by Linus Torvalds outline)
- warn only once
  (According to Linus Torvalds outline)
- Keep parent and child name in warning message
  (eases hunting for the involved parties)
---
 kernel/resource.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index c3cc6d85ec52..eb48d793aa74 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -239,7 +239,7 @@ static int __release_resource(struct resource *old, bool release_child)
 	return -EINVAL;
 }
 
-static void __release_child_resources(struct resource *r)
+static void __release_child_resources(struct resource *r, bool warn)
 {
 	struct resource *tmp, *p;
 	resource_size_t size;
@@ -252,9 +252,10 @@ static void __release_child_resources(struct resource *r)
 
 		tmp->parent = NULL;
 		tmp->sibling = NULL;
-		__release_child_resources(tmp);
+		__release_child_resources(tmp, warn);
 
-		printk(KERN_DEBUG "release child resource %pR\n", tmp);
+		if (warn)
+			printk(KERN_DEBUG "release child resource %pR\n", tmp);
 		/* need to restore size, and keep flags */
 		size = resource_size(tmp);
 		tmp->start = 0;
@@ -265,7 +266,7 @@ static void __release_child_resources(struct resource *r)
 void release_child_resources(struct resource *r)
 {
 	write_lock(&resource_lock);
-	__release_child_resources(r);
+	__release_child_resources(r, true);
 	write_unlock(&resource_lock);
 }
 
@@ -1172,7 +1173,20 @@ EXPORT_SYMBOL(__request_region);
  * @n: resource region size
  *
  * The described resource region must match a currently busy region.
+ * If the region has children they are released too.
  */
+static void check_children(struct resource *parent)
+{
+	if (parent->child) {
+		/* warn and release all children */
+		WARN_ONCE(1, "%s: %s has child %s, release all children\n",
+				__func__, parent->name, parent->child->name);
+		write_lock(&resource_lock);
+		__release_child_resources(parent, false);
+		write_unlock(&resource_lock);
+	}
+}
+
 void __release_region(struct resource *parent, resource_size_t start,
 		      resource_size_t n)
 {
@@ -1200,6 +1214,10 @@ void __release_region(struct resource *parent, resource_size_t start,
 			write_unlock(&resource_lock);
 			if (res->flags & IORESOURCE_MUXED)
 				wake_up(&muxed_resource_wait);
+
+			/* You should'nt release a resource that has children */
+			check_children(res);
+
 			free_resource(res);
 			return;
 		}
-- 
2.17.1