[PATCH 1/1] tracing: fix possible null pointer dereference

[Yuanjun Gong]

From: Gong Yuanjun <ruc_gongyuanjun@xxxxxxx>

In hist_trigger_elt_data_alloc(), elt_data is freed by
hist_elt_data_free() if kcalloc fails.

static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
{
...
elt_data->field_var_str = kcalloc(n_str, sizeof(char *), GFP_KERNEL);
        if (!elt_data->field_var_str) {
                hist_elt_data_free(elt_data);
                return -EINVAL;
        }
...}

In hist_elt_data_free() the elt_data->field_var_str field should be
checked before dereference.

Signed-off-by: Gong Yuanjun <ruc_gongyuanjun@xxxxxxx>
---
 kernel/trace/trace_events_hist.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 44db5ba9cabb..73177c9f94b2 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1576,11 +1576,11 @@ static void hist_elt_data_free(struct hist_elt_data *elt_data)
 {
 	unsigned int i;
 
-	for (i = 0; i < elt_data->n_field_var_str; i++)
-		kfree(elt_data->field_var_str[i]);
-
-	kfree(elt_data->field_var_str);
-
+	if (elt_data->field_var_str) {
+		for (i = 0; i < elt_data->n_field_var_str; i++)
+			kfree(elt_data->field_var_str[i]);
+		kfree(elt_data->field_var_str);
+	}
 	kfree(elt_data->comm);
 	kfree(elt_data);
 }
-- 
2.17.1