[PATCH 2/2] tracing: Check field value in hist_field_name()

[Steven Rostedt]

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

The function hist_field_name() cannot handle being passed a NULL field
parameter. It should never be NULL, but due to a previous bug, NULL was
passed to the function and the kernel crashed due to a NULL dereference.
Mark Rutland reported this to me on IRC.

The bug was fixed, but to prevent future bugs from crashing the kernel,
check the field and add a WARN_ON() if it is NULL.

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Mark Rutland <mark.rutland@xxxxxxx>
Fixes: c6afad49d127f ("tracing: Add hist trigger 'sym' and 'sym-offset' modifiers")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 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 6e8ab726a7b5..486cca3c2b75 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1331,6 +1331,9 @@ static const char *hist_field_name(struct hist_field *field,
 {
 	const char *field_name = "";
 
+	if (WARN_ON_ONCE(!field))
+		return field_name;
+
 	if (level > 1)
 		return field_name;
 
-- 
2.39.1