linux-kernel - [PATCH 4.1 182/267] tracing/filter: Do not WARN on operand count going below zero

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Message-Id: <20150731194008.144544346@linuxfoundation.org>
Date:	Fri, 31 Jul 2015 12:40:33 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Vince Weaver <vincent.weaver@...ne.edu>,
	Sasha Levin <sasha.levin@...cle.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH 4.1 182/267] tracing/filter: Do not WARN on operand count going below zero

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>

commit b4875bbe7e68f139bd3383828ae8e994a0df6d28 upstream.

When testing the fix for the trace filter, I could not come up with
a scenario where the operand count goes below zero, so I added a
WARN_ON_ONCE(cnt < 0) to the logic. But there is legitimate case
that it can happen (although the filter would be wrong).

 # echo '>' > /sys/kernel/debug/events/ext4/ext4_truncate_exit/filter

That is, a single operation without any operands will hit the path
where the WARN_ON_ONCE() can trigger. Although this is harmless,
and the filter is reported as a error. But instead of spitting out
a warning to the kernel dmesg, just fail nicely and report it via
the proper channels.

Link: http://lkml.kernel.org/r/558C6082.90608@oracle.com

Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
Reported-by: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/trace/trace_events_filter.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1385,7 +1385,9 @@ static int check_preds(struct filter_par
 		if (elt->op != OP_NOT)
 			cnt--;
 		n_normal_preds++;
-		WARN_ON_ONCE(cnt < 0);
+		/* all ops should have operands */
+		if (cnt < 0)
+			break;
 	}
 
 	if (cnt != 1 || !n_normal_preds || n_logical_preds >= n_normal_preds) {


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