[PATCH 4.19 28/36] tracing: Check field value in hist_field_name()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit 9f116f76fa8c04c81aef33ad870dbf9a158e5b70 upstream.

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.

Link: https://lkml.kernel.org/r/20230302020810.762384440@goodmis.org

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Mark Rutland <mark.rutland@arm.com>
Fixes: c6afad49d127f ("tracing: Add hist trigger 'sym' and 'sym-offset' modifiers")
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/trace/trace_events_hist.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1764,6 +1764,9 @@ static const char *hist_field_name(struc
 {
 	const char *field_name = "";
 
+	if (WARN_ON_ONCE(!field))
+		return field_name;
+
 	if (level > 1)
 		return field_name;