bpf: sanitize bpf tracepoint access

during bpf program loading remember the last byte of ctx access
and at the time of attaching the program to tracepoint check that
the program doesn't access bytes beyond defined in tracepoint fields

This also disallows access to __dynamic_array fields, but can be
relaxed in the future.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/events/core.c

@@ -7133,6 +7133,14 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 		return -EINVAL;
 	}
 
+	if (is_tracepoint) {
+		int off = trace_event_get_offsets(event->tp_event);
+
+		if (prog->aux->max_ctx_offset > off) {
+			bpf_prog_put(prog);
+			return -EACCES;
+		}
+	}
 	event->tp_event->prog = prog;
 
 	return 0;