In the Linux kernel, the following vulnerability has been resolved:
device property: fix infinite loop in fwnode_for_each_child_node()
When iterate over children of a fwnode that has a secondary fwnode,
fwnode_get_next_child_node() can enter an infinite loop if the secondary
fwnode has more than one child.
Parent Child
(Primary fwnode) FWa: {FWa1, FWa2, FWa3}
(Secondary fwnode) FWb: {FWb1, FWb2}
In this case:
┌─> fwnode_get_next_child_node(FWa, FWa1)
│ – fwnode_call_ptr_op(FWa, get_next_child_node, FWa1) returns FWa2
│
│ …
│
│ fwnode_get_next_child_node(FWa, FWa3)
│ – fwnode_call_ptr_op(FWa, get_next_child_node, FWa3) returns NULL
│ – fwnode_call_ptr_op(FWb, get_next_child_node, FWa3) returns FWb1
│
│ fwnode_get_next_child_node(FWa, FWb1)
│ – fwnode_call_ptr_op(FWa, get_next_child_node, FWb1) returns FWa1
└────┘
This cause fwnode_for_each_child_node() to loop indefinitely, reapeatedly
output {FWa1, FWa2, FWa3, FWb1, FWa1, …}.
The root cause is that when the current child (FWb1) belongs to the
secondary fwnode, calling get_next_child_node() on the parimary fwnode
incorrectly returns the first child (FWa1) again instead of NULL.
Fix this by dynamically checking the parent fwnode of the current child
before calling get_next_child_node(). This approach follows the pattern
established in commit b5b41ab6b0c1 (“device property: Check
fwnode->secondary in fwnode_graph_get_next_endpoint()”).
