Overview
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/67af13f8.050a0220.21dd3.0038.GAE@google.com/
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().