At 2022-06-29 21:06:17, "Pavel Machek" pavel@denx.de wrote:
Hi!
From: Liang He windhl@126.com
[ Upstream commit eb9e9bc4fa5fb489c92ec588b3fb35f042ba6d86 ]
of_find_matching_node(), of_find_compatible_node() and of_find_node_by_path() will return node pointers with refcout incremented. We should call of_node_put() when they are not used anymore.
It looks like this may introduces an use-after-free bug:
+++ b/arch/mips/pic32/pic32mzda/init.c @@ -131,13 +131,18 @@ static int __init pic32_of_prepare_platform_data(struct of_dev_auxdata *lookup) np = of_find_compatible_node(NULL, NULL, lookup->compatible); if (np) { lookup->name = (char *)np->name;
if (lookup->phys_addr)
if (lookup->phys_addr) {of_node_put(np); continue;} if (!of_address_to_resource(np, 0, &res)) lookup->phys_addr = res.start;of_node_put(np);lookup->name now contains pointer taken from np->name, but we did put() on the np. What guarantees np->name is not freed?
Best regards, Pavel
Hi, Pavel.
Thanks for you to review this patched code.
In fact, the |PUT| on 'np' will not lead to the |FREE|. First, before calling of_find_compatible_node(), the target object's refcount must be >= 1, as the object is alive. Then, after calling of_find_compatible_node(), its refcount must be >=2. So, after calling of_node_put(np), its refcount must be still >=1.
In fact, these |PUT|s are just used to keep refcount balance for the |GET| in of_find_compatible_node().
If there is anything wrong, please correct me.
Thans very much to review my patch code.
Liang
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