printk: Use scnprintf() to print the message about the dropped messages on a console

[PATCH] printk: Use scnprintf() to print the message about the dropped messages on a console

Posted by Petr Mladek 2 years, 8 months ago

Use scnprintf() for printing the message about dropped messages on
a console. It returns the really written length of the message.
It prevents potential buffer overflow when the returned length is
later used to copy the buffer content.

Note that the previous code was safe because the scratch buffer was
big enough and the message always fit in. But scnprintf() makes
it more safe, definitely.

Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1530570 ("Memory - corruptions")
Fixes: c4fcc617e148 ("printk: introduce console_prepend_dropped() for dropped messages")
Link: https://lore.kernel.org/r/202301131544.D9E804CCD@keescook
Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 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 55338bfd3b55..a9b7dade0d2e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2716,7 +2716,7 @@ static void console_prepend_dropped(struct printk_message *pmsg, unsigned long d
 	char *outbuf = &pbufs->outbuf[0];
 	size_t len;
 
-	len = snprintf(scratchbuf, scratchbuf_sz,
+	len = scnprintf(scratchbuf, scratchbuf_sz,
 		       "** %lu printk messages dropped **\n", dropped);
 
 	/*
-- 
2.35.3

Re: [PATCH] printk: Use scnprintf() to print the message about the dropped messages on a console

Posted by Petr Mladek 2 years, 7 months ago

On Tue 2023-01-17 17:10:31, Petr Mladek wrote:
> Use scnprintf() for printing the message about dropped messages on
> a console. It returns the really written length of the message.
> It prevents potential buffer overflow when the returned length is
> later used to copy the buffer content.
> 
> Note that the previous code was safe because the scratch buffer was
> big enough and the message always fit in. But scnprintf() makes
> it more safe, definitely.
> 
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1530570 ("Memory - corruptions")
> Fixes: c4fcc617e148 ("printk: introduce console_prepend_dropped() for dropped messages")
> Link: https://lore.kernel.org/r/202301131544.D9E804CCD@keescook
> Signed-off-by: Petr Mladek <pmladek@suse.com>

JFYI, the patch has been comitted into printk/linux.git,
branch rework/buffers-cleanup.

Best Regards,
Petr

Re: [PATCH] printk: Use scnprintf() to print the message about the dropped messages on a console

Posted by John Ogness 2 years, 8 months ago

On 2023-01-17, Petr Mladek <pmladek@suse.com> wrote:
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1530570 ("Memory - corruptions")
> Fixes: c4fcc617e148 ("printk: introduce console_prepend_dropped() for dropped messages")
> Link: https://lore.kernel.org/r/202301131544.D9E804CCD@keescook
> Signed-off-by: Petr Mladek <pmladek@suse.com>

Reviewed-by: John Ogness <john.ogness@linutronix.de>

Re: [PATCH] printk: Use scnprintf() to print the message about the dropped messages on a console

Posted by Sergey Senozhatsky 2 years, 7 months ago

On (23/01/17 22:54), John Ogness wrote:
> On 2023-01-17, Petr Mladek <pmladek@suse.com> wrote:
> > Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> > Addresses-Coverity-ID: 1530570 ("Memory - corruptions")
> > Fixes: c4fcc617e148 ("printk: introduce console_prepend_dropped() for dropped messages")
> > Link: https://lore.kernel.org/r/202301131544.D9E804CCD@keescook
> > Signed-off-by: Petr Mladek <pmladek@suse.com>
> 
> Reviewed-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>