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

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Date:   Tue, 17 Jan 2023 17:10:31 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        coverity-bot <keescook@...omium.org>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        linux-next@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        coverity-bot <keescook+coverity-bot@...omium.org>
Subject: [PATCH] printk: Use scnprintf() to print the message about the dropped messages on a console

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@...omium.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@...e.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