[PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

[PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

[Kuan-Wei Chiu]

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@gmail.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

Re: [PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

[Petr Mladek]

On Sat 2024-09-28 19:36:08, Kuan-Wei Chiu wrote:
> 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@gmail.com>

Looks good to me.

Acked-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

[Kuan-Wei Chiu]

On Tue, Oct 01, 2024 at 01:27:03PM +0200, Petr Mladek wrote:
> On Sat 2024-09-28 19:36:08, Kuan-Wei Chiu wrote:
> > 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@gmail.com>
> 
> Looks good to me.
> 
> Acked-by: Petr Mladek <pmladek@suse.com>
>
It has been over a month since I submitted this patch, and with only
1-2 weeks left until the next merge window opens, I still haven't seen
it included in linux-next. I'd like to check on the current status of
this patch.

Regards,
Kuan-Wei

Re: [PATCH] printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

[Petr Mladek]

On Sat 2024-09-28 19:36:08, Kuan-Wei Chiu wrote:
> 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@gmail.com>

JFYI, the patch has been committed into printk/linux.git, branch
for-6.14.

Best Regards,
Petr

PS: I am terribly sorry for missing the merge window for 6.13.
    The patch went away from my radar and I have somehow missed
    even your reminder /o\