Re: perf,ftrace: fuzzer triggers warning in trace_events_filter code

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 12 Jun 2015 21:15:10 -0400 (EDT)
Vince Weaver <vincent.weaver@maine.edu> wrote:

> On Fri, 12 Jun 2015, Steven Rostedt wrote:
> 
> > On Fri, 12 Jun 2015 17:18:22 -0400 (EDT)
> > Vince Weaver <vincent.weaver@maine.edu> wrote:
> > 
> > > 
> > > So I've modified my fuzzer to try to exercise the 
> > > PERF_EVENT_IOC_SET_FILTER ioctl() and it is starting to turn up some 
> > > warnings.
> > 
> > Is there any way to know what the filter string you used that generated
> > this?
> 
> Various seem to trigger it.  One example is
> 
> 	ext4:ext4_truncate_exit
> 	(((dev<=913)blocks==916)common_type&756)
> 

Does this patch fix your issue?

-- Steve

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 71511ebc70db..dae84db83d97 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1369,19 +1369,26 @@ static int check_preds(struct filter_parse_state *ps)
 {
 	int n_normal_preds = 0, n_logical_preds = 0;
 	struct postfix_elt *elt;
+	int cnt = 0;
 
 	list_for_each_entry(elt, &ps->postfix, list) {
-		if (elt->op == OP_NONE)
+		if (elt->op == OP_NONE) {
+			cnt++;
 			continue;
+		}
 
 		if (elt->op == OP_AND || elt->op == OP_OR) {
 			n_logical_preds++;
+			cnt--;
 			continue;
 		}
+		if (elt->op != OP_NOT)
+			cnt--;
 		n_normal_preds++;
+		WARN_ON_ONCE(cnt < 0);
 	}
 
-	if (!n_normal_preds || n_logical_preds >= n_normal_preds) {
+	if (cnt != 1 || !n_normal_preds || n_logical_preds >= n_normal_preds) {
 		parse_error(ps, FILT_ERR_INVALID_FILTER, 0);
 		return -EINVAL;
 	}