In the Linux kernel, the following vulnerability has been resolved:bpf: Defer the free of inner map when necessaryWhen updating or deleting an inner map in map array or map htab, the mapmay still be accessed by non-sleepable program or sleepable program.However bpf_map_fd_put_ptr() decreases the ref-counter of the inner mapdirectly through bpf_map_put(), if the ref-counter is the last one(which is true for most cases), the inner map will be freed byops->map_free() in a kworker. But for now, most .map_free() callbacksdon't use synchronize_rcu() or its variants to wait for the elapse of aRCU grace period, so after the invocation of ops->map_free completes,the bpf program which is accessing the inner map may incuruse-after-free problem.Fix the free of inner map by invoking bpf_map_free_deferred() after bothone RCU grace period and one tasks trace RCU grace period if the innermap has been removed from the outer map before. The deferment isaccomplished by using call_rcu() or call_rcu_tasks_trace() whenreleasing the last ref-counter of bpf map. The newly-added rcu_headfield in bpf_map shares the same storage space with work field toreduce the size of bpf_map.
