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

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Date:   Wed, 07 Oct 2020 09:24:43 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.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

Hi Steve,

On Mon, 2020-10-05 at 18:17 -0400, Steven Rostedt wrote:
> 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.
> 

Yeah, will do that next time.  Thanks for the tip.

Tom

> 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);
> 
>