From: Wen Yang Date: Fri, 3 Jan 2020 03:02:48 +0000 (+0800) Subject: ftrace: Avoid potential division by zero in function profiler X-Git-Tag: v3.16.83~94 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c59e74104cfd7df3ca0b5f59f1baee9c8c28b9ef;p=thirdparty%2Fkernel%2Fstable.git 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 Fixes: e330b3bcd8319 ("tracing: Show sample std dev in function profiling") Fixes: 34886c8bc590f ("tracing: add average time in function to function profiler") Signed-off-by: Wen Yang Signed-off-by: Steven Rostedt (VMware) [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index c59d43d54d321..ff5281a9c5d7c 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -595,8 +595,7 @@ static int function_stat_show(struct seq_file *m, void *v) #ifdef CONFIG_FUNCTION_GRAPH_TRACER seq_printf(m, " "); - avg = rec->time; - do_div(avg, rec->counter); + avg = div64_ul(rec->time, rec->counter); /* Sample standard deviation (s^2) */ if (rec->counter <= 1) @@ -613,7 +612,8 @@ 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);