netdev - [PATCH net-next] can: slcan: use scnprintf() as a hardening measure

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Date:   Wed, 6 Jul 2022 10:59:48 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Wolfgang Grandegger <wg@...ndegger.com>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: [PATCH net-next] can: slcan: use scnprintf() as a hardening measure

The snprintf() function returns the number of bytes which *would* have
been copied if there were no space.  So, since this code does not check
the return value, there if the buffer was not large enough then there
would be a buffer overflow two lines later when it does:

	actual = sl->tty->ops->write(sl->tty, sl->xbuff, n);

Use scnprintf() instead because that returns the number of bytes which
were actually copied.

Fixes: 52f9ac85b876 ("can: slcan: allow to send commands to the adapter")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 drivers/net/can/slcan/slcan-core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
index 54d29a410ad5..92bdd49996d1 100644
--- a/drivers/net/can/slcan/slcan-core.c
+++ b/drivers/net/can/slcan/slcan-core.c
@@ -647,7 +647,7 @@ static int slcan_transmit_cmd(struct slcan *sl, const unsigned char *cmd)
 		return -ENODEV;
 	}
 
-	n = snprintf(sl->xbuff, sizeof(sl->xbuff), "%s", cmd);
+	n = scnprintf(sl->xbuff, sizeof(sl->xbuff), "%s", cmd);
 	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
 	actual = sl->tty->ops->write(sl->tty, sl->xbuff, n);
 	sl->xleft = n - actual;
-- 
2.35.1