linux-kernel - [PATCH] tracing: devlink: Use dynamic size for string in devlink_trap

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Date:   Sun, 3 Jul 2022 11:18:09 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Jakub Kicinski <kuba@...nel.org>, Leon Romanovsky <leon@...nel.org>
Subject: [PATCH] tracing: devlink: Use dynamic size for string in
 devlink_trap_report event

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

The trace event devlink_trap_report uses the __dynamic_array() macro to
determine the size of the input_dev_name field. This is because it needs
to test the dev field for NULL, and will use "NULL" if it is. But it also
has the size of the dynamic array as a fixed IFNAMSIZ bytes. This defeats
the purpose of the dynamic array, as this will reserve that amount of
bytes on the ring buffer, and to make matters worse, it will even save
that size in the event as the event expects it to be dynamic (for which it
is not).

Instead, add the logic to calculate the size needed to save the
input_dev_name field and only allocate that on the ring buffer.

Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Leon Romanovsky <leon@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 include/trace/events/devlink.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/trace/events/devlink.h b/include/trace/events/devlink.h
index 2814f188d98c..93c2783609de 100644
--- a/include/trace/events/devlink.h
+++ b/include/trace/events/devlink.h
@@ -186,7 +186,7 @@ TRACE_EVENT(devlink_trap_report,
 		__string(driver_name, devlink_to_dev(devlink)->driver->name)
 		__string(trap_name, metadata->trap_name)
 		__string(trap_group_name, metadata->trap_group_name)
-		__dynamic_array(char, input_dev_name, IFNAMSIZ)
+		__dynamic_array(char, input_dev_name, input_dev ? strlen(input_dev->name) + 1 : sizeof("NULL"))
 	),

 	TP_fast_assign(
-- 
2.35.1