linux-kernel - [PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN

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Message-Id: <20240928113608.1438087-1-visitorckw@gmail.com>
Date: Sat, 28 Sep 2024 19:36:08 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: Petr Mladek <pmladek@...e.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Ching-Chun Huang <jserv@...s.ncku.edu.tw>,
	linux-kernel@...r.kernel.org,
	Kuan-Wei Chiu <visitorckw@...il.com>
Subject: [PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

Shifting 1 << 31 on a 32-bit int causes signed integer overflow, which
leads to undefined behavior. To prevent this, cast 1 to u32 before
performing the shift, ensuring well-defined behavior.

This change explicitly avoids any potential overflow by ensuring that
the shift occurs on an unsigned 32-bit integer.

Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
Note: Build test only.

 kernel/printk/printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index beb808f4c367..ea0b2290e2d1 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -523,7 +523,7 @@ static struct latched_seq clear_seq = {
 /* record buffer */
 #define LOG_ALIGN __alignof__(unsigned long)
 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
-#define LOG_BUF_LEN_MAX (u32)(1 << 31)
+#define LOG_BUF_LEN_MAX ((u32)1 << 31)
 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
 static char *log_buf = __log_buf;
 static u32 log_buf_len = __LOG_BUF_LEN;
-- 
2.34.1