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    Subject[PATCH 5.4 131/191] ftrace: Avoid potential division by zero in function profiler
    Date
    From: Wen Yang <wenyang@linux.alibaba.com>

    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: 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 <wenyang@linux.alibaba.com>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/kernel/trace/ftrace.c
    +++ b/kernel/trace/ftrace.c
    @@ -524,8 +524,7 @@ static int function_stat_show(struct seq
    }

    #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
    @@ -551,7 +550,8 @@ static int function_stat_show(struct seq
    * 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);

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