Re: [PATCH v3 0/3] tracing: Add dynamic strings for synthetic events

[Steven Rostedt <rostedt@goodmis.org>]

On Thu,  1 Oct 2020 16:46:43 -0500
Tom Zanussi <zanussi@kernel.org> wrote:

> Hi,
> 
> This is v3 of the dynamic string support for synthetic events.
> 
> No code changes since v2, just added Fixes: tag for 'tracing: Fix
> parse_synth_field() error handling' as suggested by Masami along with
> his Reviewed-by, and Axel's Tested-bys.
> 

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.

-- Steve

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 4b3ec570147a..d81739990a53 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);