Commit e31f7939 authored Jan 03, 2020 by Wen Yang Committed by Steven Rostedt (VMware) Jan 02, 2020

ftrace: Avoid potential division by zero in function profiler

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.

Link: http://lkml.kernel.org/r/20200103030248.14516-1-wenyang@linux.alibaba.com



Cc: stable@vger.kernel.org
Fixes: e330b3bc ("tracing: Show sample std dev in function profiling")
Fixes: 34886c8b ("tracing: add average time in function to function profiler")
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent b8299d36

kernel/trace/ftrace.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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);

Admin message