batadv_neigh_node_create() is used to create a neigh node object, whose
fields will be initialized with the specific object. When a new
reference of the specific object is created during the initialization,
its refcount should be increased.
However, when "neigh_node" object initializes its orig_node field with
the "orig_node" object, the function forgets to hold the refcount of the
"orig_node", causing a potential refcount leak and use-after-free issue
for the reason that the object can be freed in other places.
Fix this issue by increasing the refcount of orig_node object during the
initialization and adding corresponding batadv_orig_node_put() in
batadv_neigh_node_release().
Signed-off-by: Xiyu Yang <[email protected]>
Signed-off-by: Xin Tan <[email protected]>
---
net/batman-adv/originator.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index 805d8969bdfb..d6c2296f8e35 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -306,6 +306,8 @@ static void batadv_neigh_node_release(struct kref *ref)
batadv_hardif_put(neigh_node->if_incoming);
+ batadv_orig_node_put(neigh_node->orig_node);
+
kfree_rcu(neigh_node, rcu);
}
@@ -685,6 +687,7 @@ batadv_neigh_node_create(struct batadv_orig_node *orig_node,
kref_get(&hard_iface->refcount);
ether_addr_copy(neigh_node->addr, neigh_addr);
neigh_node->if_incoming = hard_iface;
+ kref_get(&orig_node->refcount);
neigh_node->orig_node = orig_node;
neigh_node->last_seen = jiffies;
--
2.7.4
On Friday, 18 September 2020 05:03:19 CEST Xiyu Yang wrote:
> batadv_neigh_node_create() is used to create a neigh node object, whose
> fields will be initialized with the specific object. When a new
> reference of the specific object is created during the initialization,
> its refcount should be increased.
>
> However, when "neigh_node" object initializes its orig_node field with
> the "orig_node" object, the function forgets to hold the refcount of the
> "orig_node", causing a potential refcount leak and use-after-free issue
> for the reason that the object can be freed in other places.
>
> Fix this issue by increasing the refcount of orig_node object during the
> initialization and adding corresponding batadv_orig_node_put() in
> batadv_neigh_node_release().
I will most likely not add this patch because I have concerns that this would
need an active garbage collector to fix the reference counter loop.
Please check batadv_neigh_node::orig_node (whose reference counter you've just
incremented) and batadv_orig_node::neigh_list (with batadv_neigh_node). And at
the same time the batadv_neigh_node_release and batadv_orig_node_release. So
the originator will only free the reference (and thus potentially call
batadv_neigh_node_release) when its own reference counter is zero. But it
cannot become zero because the neigh_node is holding a reference to this
originator.
Kind regards,
Sven