bpf: Fix UAF via mismatching bpf_prog/attachment RCU flavors

Uprobes always use bpf_prog_run_array_uprobe() under tasks-trace-RCU
protection. But it is possible to attach a non-sleepable BPF program to a
uprobe, and non-sleepable BPF programs are freed via normal RCU (see
__bpf_prog_put_noref()). This leads to UAF of the bpf_prog because a normal
RCU grace period does not imply a tasks-trace-RCU grace period.

Fix it by explicitly waiting for a tasks-trace-RCU grace period after
removing the attachment of a bpf_prog to a perf_event.

Fixes: 8c7dcb8 ("bpf: implement sleepable uprobes by chaining gps")
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/bpf/20241210-bpf-fix-actual-uprobe-uaf-v1-1-19439849dd44@google.com

Author: thejh

kernel/trace/bpf_trace.c

@@ -2258,6 +2258,13 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
 		bpf_prog_array_free_sleepable(old_array);
 	}
 
+	/*
+	 * It could be that the bpf_prog is not sleepable (and will be freed
+	 * via normal RCU), but is called from a point that supports sleepable
+	 * programs and uses tasks-trace-RCU.
+	 */
+	synchronize_rcu_tasks_trace();
+
 	bpf_prog_put(event->prog);
 	event->prog = NULL;