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

[Steven Rostedt <rostedt@kernel.org>]

From: Steven Rostedt <rostedt@goodmis.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@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