linux-kernel - Re: [PATCH v4 7/7] tracing: Change synthetic event string format to limit printed length

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Date:   Mon, 5 Oct 2020 18:17:51 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <zanussi@...nel.org>
Cc:     axelrasmussen@...gle.com, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/7] tracing: Change synthetic event string format to
 limit printed length

On Sun,  4 Oct 2020 17:14:09 -0500
Tom Zanussi <zanussi@...nel.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> Change the format for printing synthetic field strings to limit the
> length of the string printed even if it's not correctly terminated.
> 
> Description from Steve:
> 
> I also added this for a bit of paranoid, and probably should be a
> separate patch, just to make sure if the string isn't nul terminated,
> this will keep it from bleeding pass the end of the string.

Just FYI. In the future, for something like this, you should still have
your own Signed-off-by, as you are sending it (and part of the commit
path). You could also add:

[ Need signed-off-by from Steven ]

Which I would have also added as well.

Thanks!

-- Steve


> ---
>  kernel/trace/trace_events_synth.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
> index 24bc6d61aa40..742ce5f62d6d 100644
> --- a/kernel/trace/trace_events_synth.c
> +++ b/kernel/trace/trace_events_synth.c
> @@ -234,7 +234,7 @@ static const char *synth_field_fmt(char *type)
>  	else if (strcmp(type, "gfp_t") == 0)
>  		fmt = "%x";
>  	else if (synth_field_is_string(type))
> -		fmt = "%s";
> +		fmt = "%.*s";
>  
>  	return fmt;
>  }
> @@ -303,11 +303,13 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
>  				str_field = (char *)entry + data_offset;
>  
>  				trace_seq_printf(s, print_fmt, se->fields[i]->name,
> +						 STR_VAR_LEN_MAX,
>  						 str_field,
>  						 i == se->n_fields - 1 ? "" : " ");
>  				n_u64++;
>  			} else {
>  				trace_seq_printf(s, print_fmt, se->fields[i]->name,
> +						 STR_VAR_LEN_MAX,
>  						 (char *)&entry->fields[n_u64],
>  						 i == se->n_fields - 1 ? "" : " ");
>  				n_u64 += STR_VAR_LEN_MAX / sizeof(u64);