printk: fix string termination for record_print_text()

stable inclusion
from stable-5.10.12
commit d5ac8304e18025a522b5d1d87629e926064ce134
bugzilla: 47876

--------------------------------

commit 08d60e59 upstream.

Commit f0e386ee ("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: f0e386ee ("printk: fix buffer overflow potential for print_text()")
Reported-by: NSven Schnelle <svens@linux.ibm.com>
Signed-off-by: NJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210124202728.4718-1-john.ogness@linutronix.deSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

kernel/printk/printk.c

@@ -1445,7 +1445,7 @@ 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;
 }