linux-kernel - [PATCH v4 12/13] tracing: Check for printable characters when printing field dyn strings

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Message-ID: <20251021005234.245481539@kernel.org>
Date: Mon, 20 Oct 2025 20:52:07 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Takaya Saeki <takayas@...gle.com>,
 Tom Zanussi <zanussi@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Ian Rogers <irogers@...gle.com>,
 Douglas Raillard <douglas.raillard@....com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Ingo Molnar <mingo@...hat.com>
Subject: [PATCH v4 12/13] tracing: Check for printable characters when printing field dyn
 strings

From: Steven Rostedt <rostedt@...dmis.org>

When the "fields" option is enabled, it prints each trace event field
based on its type. But a dynamic array and a dynamic string can both have
a "char *" type. Printing it as a string can cause escape characters to be
printed and mess up the output of the trace.

For dynamic strings, test if there are any non-printable characters, and
if so, print both the string with the non printable characters as '.', and
the print the hex value of the array.

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_output.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 97db0b0ccf3e..718b255b6fd8 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -950,7 +950,9 @@ static void print_fields(struct trace_iterator *iter, struct trace_event_call *c
 	int offset;
 	int len;
 	int ret;
+	int i;
 	void *pos;
+	char *str;
 
 	list_for_each_entry_reverse(field, head, link) {
 		trace_seq_printf(&iter->seq, " %s=", field->name);
@@ -977,8 +979,29 @@ static void print_fields(struct trace_iterator *iter, struct trace_event_call *c
 				trace_seq_puts(&iter->seq, "<OVERFLOW>");
 				break;
 			}
-			pos = (void *)iter->ent + offset;
-			trace_seq_printf(&iter->seq, "%.*s", len, (char *)pos);
+			str = (char *)iter->ent + offset;
+			/* Check if there's any non printable strings */
+			for (i = 0; i < len; i++) {
+				if (str[i] && !(isascii(str[i]) && isprint(str[i])))
+					break;
+			}
+			if (i < len) {
+				for (i = 0; i < len; i++) {
+					if (isascii(str[i]) && isprint(str[i]))
+						trace_seq_putc(&iter->seq, str[i]);
+					else
+						trace_seq_putc(&iter->seq, '.');
+				}
+				trace_seq_puts(&iter->seq, " (");
+				for (i = 0; i < len; i++) {
+					if (i)
+						trace_seq_putc(&iter->seq, ':');
+					trace_seq_printf(&iter->seq, "%02x", str[i]);
+				}
+				trace_seq_putc(&iter->seq, ')');
+			} else {
+				trace_seq_printf(&iter->seq, "%.*s", len, str);
+			}
 			break;
 		case FILTER_PTR_STRING:
 			if (!iter->fmt_size)
-- 
2.51.0