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

Steven Rostedt
2025-10-21T00:52:13Z

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@goodmis.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