linux-kernel - [PATCH v2] ftrace: avoid potential division by zero

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Message-Id: <20200103030248.14516-1-wenyang@linux.alibaba.com>
Date:   Fri,  3 Jan 2020 11:02:48 +0800
From:   Wen Yang <wenyang@...ux.alibaba.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     xlpang@...ux.alibaba.com, Wen Yang <wenyang@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] ftrace: avoid potential division by zero

The ftrace_profile->counter is unsigned long and
do_div truncates it to 32 bits, which means it can test
non-zero and be truncated to zero for division.
Fix this issue by using div64_ul() instead.

Signed-off-by: Wen Yang <wenyang@...ux.alibaba.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org
---
v2: get rid of the pre-assigning of avg.

 kernel/trace/ftrace.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index ac99a35..9bf1f2c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -526,8 +526,7 @@ static int function_stat_show(struct seq_file *m, void *v)
 	}
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	avg = rec->time;
-	do_div(avg, rec->counter);
+	avg = div64_ul(rec->time, rec->counter);
 	if (tracing_thresh && (avg < tracing_thresh))
 		goto out;
 #endif
@@ -553,7 +552,8 @@ static int function_stat_show(struct seq_file *m, void *v)
 		 * Divide only 1000 for ns^2 -> us^2 conversion.
 		 * trace_print_graph_duration will divide 1000 again.
 		 */
-		do_div(stddev, rec->counter * (rec->counter - 1) * 1000);
+		stddev = div64_ul(stddev,
+				  rec->counter * (rec->counter - 1) * 1000);
 	}
 
 	trace_seq_init(&s);
-- 
1.8.3.1