[PATCH v2 1/2] tracing/hist: rebuild full_name on each hist_field_name() call

[Pengpeng Hou <pengpeng@iscas.ac.cn>]

hist_field_name() uses a static MAX_FILTER_STR_VAL buffer for fully
qualified variable-reference names, but it currently appends into that
buffer with strcat() without rebuilding it first. As a result, repeated
calls append a new "system.event.field" name onto the previous one,
which can eventually run past the end of full_name.

Build the name with snprintf() on each call and return NULL if the fully
qualified name does not fit in MAX_FILTER_STR_VAL.

Fixes: 067fe038e70f ("tracing: Add variable reference handling to hist triggers")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
v2:
- rebuild full_name on each call instead of falling back to field->name
- return NULL on overflow as suggested
- split out the snprintf() length check instead of using an inline if

 kernel/trace/trace_events_hist.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 73ea180cad55..f9c8a4f078ea 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1361,12 +1361,14 @@ static const char *hist_field_name(struct hist_field *field,
 		 field->flags & HIST_FIELD_FL_VAR_REF) {
 		if (field->system) {
 			static char full_name[MAX_FILTER_STR_VAL];
+			int len;
+
+			len = snprintf(full_name, sizeof(full_name), "%s.%s.%s",
+				       field->system, field->event_name,
+				       field->name);
+			if (len >= sizeof(full_name))
+				return NULL;
 
-			strcat(full_name, field->system);
-			strcat(full_name, ".");
-			strcat(full_name, field->event_name);
-			strcat(full_name, ".");
-			strcat(full_name, field->name);
 			field_name = full_name;
 		} else
 			field_name = field->name;
-- 
2.50.1 (Apple Git-155)