[PATCH] tracing: Fix potential double free in create_var_ref()

[Keita Suzuki <keitasuzuki.park@sslab.ics.keio.ac.jp>]

In create_var_ref(), init_var_ref() is called to initialize the fields
of variable ref_field, which is allocated in the previous function call
to create_hist_field(). Function init_var_ref() allocates the
corresponding fields such as ref_field->system, but frees these fields
when the function encounters an error. The caller later calls
destroy_hist_field() to conduct error handling, which frees the fields
and the variable itself. This results in double free of the fields which
are already freed in the previous function.

Fix this by storing NULL to the corresponding fields when they are freed
in init_var_ref().

Signed-off-by: Keita Suzuki <keitasuzuki.park@sslab.ics.keio.ac.jp>
---
 kernel/trace/trace_events_hist.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 44db5ba9cabb..a0e41906d9ce 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2093,8 +2093,11 @@ static int init_var_ref(struct hist_field *ref_field,
 	return err;
  free:
 	kfree(ref_field->system);
+	ref_field->system = NULL;
 	kfree(ref_field->event_name);
+	ref_field->event_name = NULL;
 	kfree(ref_field->name);
+	ref_field->name = NULL;
 
 	goto out;
 }
-- 
2.25.1