CVE-2023-52447

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

bpf: Defer the free of inner map when necessary

When updating or deleting an inner map in map array or map htab, the map

may still be accessed by non-sleepable program or sleepable program.

However bpf_map_fd_put_ptr() decreases the ref-counter of the inner map

directly through bpf_map_put(), if the ref-counter is the last one

(which is true for most cases), the inner map will be freed by

ops->map_free() in a kworker. But for now, most .map_free() callbacks

don't use synchronize_rcu() or its variants to wait for the elapse of a

RCU grace period, so after the invocation of ops->map_free completes,

the bpf program which is accessing the inner map may incur

use-after-free problem.

Fix the free of inner map by invoking bpf_map_free_deferred() after both

one RCU grace period and one tasks trace RCU grace period if the inner

map has been removed from the outer map before. The deferment is

accomplished by using call_rcu() or call_rcu_tasks_trace() when

releasing the last ref-counter of bpf map. The newly-added rcu_head

field in bpf_map shares the same storage space with work field to

reduce the size of bpf_map.