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Commit 010a7e84 authored by Wen Yang's avatar Wen Yang Committed by Greg Kroah-Hartman
Browse files

ftrace: Avoid potential division by zero in function profiler 

commit e31f7939c1c27faa5d0e3f14519eaf7c89e8a69d upstream.

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: default avatarWen Yang <wenyang@linux.alibaba.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d89a351b

kernel/trace/ftrace.c

+3 −3
Original line number Diff line number Diff line
@@ -554,8 +554,7 @@ 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
@@ -581,7 +580,8 @@ 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);