[PATCH v2] tracing: Add size check when printing trace_marker output

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

If for some reason the trace_marker write does not have a nul byte for the
string, it will overflow the print:

  trace_seq_printf(s, ": %s", field->buf);

The field->buf could be missing the nul byte. To prevent overflow, add the
max size that the buf can be by using the event size and the field
location.

  int max = iter->ent_size - offsetof(struct print_entry, buf);

  trace_seq_printf(s, ": %*.s", max, field->buf);

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
Changes since v1: https://lore.kernel.org/linux-trace-kernel/20231212084444.4619b8ce@xxxxxxxxxxxxxxxxxx

- Use "%.*s" and not "%*s" otherwise it right aligns the output.

[ Masami, I kept your review by. ]

 kernel/trace/trace_output.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d01083..3e7fa44dc2b2 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1587,11 +1587,12 @@ static enum print_line_t trace_print_print(struct trace_iterator *iter,
 {
 	struct print_entry *field;
 	struct trace_seq *s = &iter->seq;
+	int max = iter->ent_size - offsetof(struct print_entry, buf);
 
 	trace_assign_type(field, iter->ent);
 
 	seq_print_ip_sym(s, field->ip, flags);
-	trace_seq_printf(s, ": %s", field->buf);
+	trace_seq_printf(s, ": %.*s", max, field->buf);
 
 	return trace_handle_return(s);
 }
@@ -1600,10 +1601,11 @@ static enum print_line_t trace_print_raw(struct trace_iterator *iter, int flags,
 					 struct trace_event *event)
 {
 	struct print_entry *field;
+	int max = iter->ent_size - offsetof(struct print_entry, buf);
 
 	trace_assign_type(field, iter->ent);
 
-	trace_seq_printf(&iter->seq, "# %lx %s", field->ip, field->buf);
+	trace_seq_printf(&iter->seq, "# %lx %.*s", field->ip, max, field->buf);
 
 	return trace_handle_return(&iter->seq);
 }
-- 
2.42.0