CVE-2025-38212: Use After Free

In the Linux kernel, the following vulnerability has been resolved:

ipc: fix to protect IPCS lookups using RCU

syzbot reported that it discovered a use-after-free vulnerability, [0]

[0]: https://lore.kernel.org/all/[email protected]/

idr_for_each() is protected by rwsem, but this is not enough. If it is not protected by RCU read-critical region, when idr_for_each() calls radix_tree_node_free() through call_rcu() to free the radix_tree_node structure, the node will be freed immediately, and when reading the next node in radix_tree_for_each_slot(), the already freed memory may be read.

Therefore, we need to add code to make sure that idr_for_each() is protected within the RCU read-critical region when we call it in shm_destroy_orphaned().