CVE-2023-52483

In the Linux kernel, the following vulnerability has been resolved: mctp:
perform route lookups under a RCU read-side lock Our current route lookups
(mctp_route_lookup and mctp_route_lookup_null) traverse the net’s route
list without the RCU read lock held. This means the route lookup is subject
to preemption, resulting in an potential grace period expiry, and so an
eventual kfree() while we still have the route pointer. Add the proper
read-side critical section locks around the route lookups, preventing
premption and a possible parallel kfree. The remaining net->mctp.routes
accesses are already under a rcu_read_lock, or protected by the RTNL for
updates. Based on an analysis from Sili Luo <[email protected]>, where
introducing a delay in the route lookup could cause a UAF on simultaneous
sendmsg() and route deletion.