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Subject[PATCH v2] kernel/resource.c: invalidate parent when freed resource has childs
Date
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
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