[PATCH] printk: fix string termination for record_print_text()

[PATCH] printk: fix string termination for record_print_text()

[John Ogness]

Commit f0e386ee0c0b ("printk: fix buffer overflow potential for
print_text()") added string termination in record_print_text().
However it used the wrong base pointer for adding the terminator.
This led to a 0-byte being written somewhere beyond the buffer.

Use the correct base pointer when adding the terminator.

Fixes: f0e386ee0c0b ("printk: fix buffer overflow potential for print_text()")
Reported-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 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 6639a0cfe0ac..5a95c688621f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1398,7 +1398,7 @@ static size_t record_print_text(struct printk_record *r, bool syslog,
 	 * not counted in the return value.
 	 */
 	if (buf_size > 0)
-		text[len] = 0;
+		r->text_buf[len] = 0;
 
 	return len;
 }
-- 
2.20.1

Re: [PATCH] printk: fix string termination for record_print_text()

[Petr Mladek]

On Sun 2021-01-24 21:33:28, John Ogness wrote:
> Commit f0e386ee0c0b ("printk: fix buffer overflow potential for
> print_text()") added string termination in record_print_text().
> However it used the wrong base pointer for adding the terminator.
> This led to a 0-byte being written somewhere beyond the buffer.
> 
> Use the correct base pointer when adding the terminator.
> 
> Fixes: f0e386ee0c0b ("printk: fix buffer overflow potential for print_text()")
> Reported-by: Sven Schnelle <svens@linux.ibm.com>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

The patch is pushed in kernel/printk.git, branch printk-rework.

I am going to send pull request for-5.11 later today.

Thanks a lot for the debugging and quick fix. I feel shame that
I did not caught this during the review.

Best Regards,
Petr