tracing: Rebuild full_name on each hist_field_name() call

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.

Link: https://patch.msgid.link/20260401112224.85582-1-pengpeng@iscas.ac.cn
Fixes: 067fe038e70f ("tracing: Add variable reference handling to hist triggers")
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Tested-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 67cb923..b2b675c 100644 (file)
--- 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;