linux-kernel - [PATCH AUTOSEL 6.1 2/9] printk: Fix signed integer overflow when defining LOG_BUF_LEN

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Message-Id: <20250126145651.943149-2-sashal@kernel.org>
Date: Sun, 26 Jan 2025 09:56:44 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Kuan-Wei Chiu <visitorckw@...il.com>,
	Petr Mladek <pmladek@...e.com>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 6.1 2/9] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

From: Kuan-Wei Chiu <visitorckw@...il.com>

[ Upstream commit 3d6f83df8ff2d5de84b50377e4f0d45e25311c7a ]

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>
Acked-by: Petr Mladek <pmladek@...e.com>
Link: https://lore.kernel.org/r/20240928113608.1438087-1-visitorckw@gmail.com
Signed-off-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 5a88134fba79f..c93beab96c860 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -403,7 +403,7 @@ 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;
-- 
2.39.5