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    Subject[PATCH 4.14 081/183] tracing: Use strncpy instead of memcpy for string keys in hist triggers
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tom Zanussi <tom.zanussi@linux.intel.com>

    commit 9f0bbf3115ca9f91f43b7c74e9ac7d79f47fc6c2 upstream.

    Because there may be random garbage beyond a string's null terminator,
    it's not correct to copy the the complete character array for use as a
    hist trigger key. This results in multiple histogram entries for the
    'same' string key.

    So, in the case of a string key, use strncpy instead of memcpy to
    avoid copying in the extra bytes.

    Before, using the gdbus entries in the following hist trigger as an
    example:

    # echo 'hist:key=comm' > /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
    # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist

    ...

    { comm: ImgDecoder #4 } hitcount: 203
    { comm: gmain } hitcount: 213
    { comm: gmain } hitcount: 216
    { comm: StreamTrans #73 } hitcount: 221
    { comm: mozStorage #3 } hitcount: 230
    { comm: gdbus } hitcount: 233
    { comm: StyleThread#5 } hitcount: 253
    { comm: gdbus } hitcount: 256
    { comm: gdbus } hitcount: 260
    { comm: StyleThread#4 } hitcount: 271

    ...

    # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist | egrep gdbus | wc -l
    51

    After:

    # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist | egrep gdbus | wc -l
    1

    Link: http://lkml.kernel.org/r/50c35ae1267d64eee975b8125e151e600071d4dc.1549309756.git.tom.zanussi@linux.intel.com

    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: stable@vger.kernel.org
    Fixes: 79e577cbce4c4 ("tracing: Support string type key properly")
    Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/trace/trace_events_hist.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/kernel/trace/trace_events_hist.c
    +++ b/kernel/trace/trace_events_hist.c
    @@ -872,9 +872,10 @@ static inline void add_to_key(char *comp
    /* ensure NULL-termination */
    if (size > key_field->size - 1)
    size = key_field->size - 1;
    - }

    - memcpy(compound_key + key_field->offset, key, size);
    + strncpy(compound_key + key_field->offset, (char *)key, size);
    + } else
    + memcpy(compound_key + key_field->offset, key, size);
    }

    static void event_hist_trigger(struct event_trigger_data *data, void *rec)

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