From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from metis.whiteo.stw.pengutronix.de (metis.whiteo.stw.pengutronix.de [185.203.201.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C95A031771E for ; Tue, 23 Sep 2025 07:42:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.203.201.7 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758613381; cv=none; b=WWPdrivRyAvXwHEWOukSCFU9jbLEfLBIQ901WqBzLcKO6i1BMarMSwPUqO5BkqDl29PnLXCBz2hGuaVkLR13jvR4lyw3uyQtCisvIbaB6A2MmZUxKdPrk/zjED08ygtxbgjmPuW+itGsCw16r39Ayirs9J1YFwVEaMvWHHBIfiE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758613381; c=relaxed/simple; bh=3m9eC7t0D0zlyp+Qb62ggaSqoqeHcwSN8r6+vJRKhAI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=C/mGGmV25V8RUeJWfj7XXKYSejhwBfJXYS1wbHUPwJTJ5qy7TeCqF4KB32QK0PzCnwfCxtnhT3/r0PHppuHaa7Y9QnoHlH2Q9Lrl2y0kvvk/Wyg8zmGtZoDbOczqJiVOJc4KCKwLUyqaG5MnBrWYxZDVr5Iv89m+47p6pNu6T6w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de; spf=pass smtp.mailfrom=pengutronix.de; arc=none smtp.client-ip=185.203.201.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pengutronix.de Received: from drehscheibe.grey.stw.pengutronix.de ([2a0a:edc0:0:c01:1d::a2]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1v0xfg-0003cf-QX; Tue, 23 Sep 2025 09:42:44 +0200 Received: from moin.white.stw.pengutronix.de ([2a0a:edc0:0:b01:1d::7b] helo=bjornoya.blackshift.org) by drehscheibe.grey.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1v0xff-0003NR-2D; Tue, 23 Sep 2025 09:42:43 +0200 Received: from blackshift.org (p54b152ce.dip0.t-ipconnect.de [84.177.82.206]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) (Authenticated sender: mkl-all@blackshift.org) by smtp.blackshift.org (Postfix) with ESMTPSA id 19A40477A8D; Tue, 23 Sep 2025 07:34:32 +0000 (UTC) From: Marc Kleine-Budde To: netdev@vger.kernel.org Cc: davem@davemloft.net, kuba@kernel.org, linux-can@vger.kernel.org, kernel@pengutronix.de, Vincent Mailhol , Marc Kleine-Budde Subject: [PATCH net 6/7] can: mcba_usb: populate ndo_change_mtu() to prevent buffer overflow Date: Tue, 23 Sep 2025 09:32:52 +0200 Message-ID: <20250923073427.493034-7-mkl@pengutronix.de> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250923073427.493034-1-mkl@pengutronix.de> References: <20250923073427.493034-1-mkl@pengutronix.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2a0a:edc0:0:c01:1d::a2 X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.whiteo.stw.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: netdev@vger.kernel.org From: Vincent Mailhol Sending an PF_PACKET allows to bypass the CAN framework logic and to directly reach the xmit() function of a CAN driver. The only check which is performed by the PF_PACKET framework is to make sure that skb->len fits the interface's MTU. Unfortunately, because the mcba_usb driver does not populate its net_device_ops->ndo_change_mtu(), it is possible for an attacker to configure an invalid MTU by doing, for example: $ ip link set can0 mtu 9999 After doing so, the attacker could open a PF_PACKET socket using the ETH_P_CANXL protocol: socket(PF_PACKET, SOCK_RAW, htons(ETH_P_CANXL)) to inject a malicious CAN XL frames. For example: struct canxl_frame frame = { .flags = 0xff, .len = 2048, }; The CAN drivers' xmit() function are calling can_dev_dropped_skb() to check that the skb is valid, unfortunately under above conditions, the malicious packet is able to go through can_dev_dropped_skb() checks: 1. the skb->protocol is set to ETH_P_CANXL which is valid (the function does not check the actual device capabilities). 2. the length is a valid CAN XL length. And so, mcba_usb_start_xmit() receives a CAN XL frame which it is not able to correctly handle and will thus misinterpret it as a CAN frame. This can result in a buffer overflow. The driver will consume cf->len as-is with no further checks on these lines: usb_msg.dlc = cf->len; memcpy(usb_msg.data, cf->data, usb_msg.dlc); Here, cf->len corresponds to the flags field of the CAN XL frame. In our previous example, we set canxl_frame->flags to 0xff. Because the maximum expected length is 8, a buffer overflow of 247 bytes occurs! Populate net_device_ops->ndo_change_mtu() to ensure that the interface's MTU can not be set to anything bigger than CAN_MTU. By fixing the root cause, this prevents the buffer overflow. Fixes: 51f3baad7de9 ("can: mcba_usb: Add support for Microchip CAN BUS Analyzer") Signed-off-by: Vincent Mailhol Link: https://patch.msgid.link/20250918-can-fix-mtu-v1-4-0d1cada9393b@kernel.org Signed-off-by: Marc Kleine-Budde --- drivers/net/can/usb/mcba_usb.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/can/usb/mcba_usb.c b/drivers/net/can/usb/mcba_usb.c index 41c0a1c399bf..1f9b915094e6 100644 --- a/drivers/net/can/usb/mcba_usb.c +++ b/drivers/net/can/usb/mcba_usb.c @@ -761,6 +761,7 @@ static const struct net_device_ops mcba_netdev_ops = { .ndo_open = mcba_usb_open, .ndo_stop = mcba_usb_close, .ndo_start_xmit = mcba_usb_start_xmit, + .ndo_change_mtu = can_change_mtu, }; static const struct ethtool_ops mcba_ethtool_ops = { -- 2.51.0