In the Linux kernel, the following vulnerability has been resolved: fprobe: Fix...

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

fprobe: Fix unregister_fprobe() to wait for RCU grace period

Commit 4346ba1604093 ("fprobe: Rewrite fprobe on function-graph tracer") changed fprobe to register struct fprobe to an rcu-hlist, but it forgot to wait for RCU GP. Thus there can be use-after-free if the fprobe is released right after unregistering. This can be happened on fprobe event and sample module code.

To fix this issue, add synchronize_rcu() in unregister_fprobe().

Note that BPF is OK because fprobe is used as a part of bpf_kprobe_multi_link. This unregisters its fprobe in bpf_kprobe_multi_link_release() and it is deallocated via bpf_kprobe_multi_link_dealloc(), which is invoked from bpf_link_defer_dealloc_rcu_gp() RCU callback.

For BPF, this also introduced unregister_fprobe_async() which does NOT wait for RCU grace priod.