From nobody Thu Oct 2 10:38:49 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 8A8683002C4; Thu, 18 Sep 2025 09:01:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758186117; cv=none; b=ZD6FHIGPyncvDfugzh9bnHvzJkWRZzqS3KIyz9Cwf2mqPyeDC1o36ly9FEQhlcUsxB07vn0fhS6AYopAkNhVdGJ0GdJTadfG267MBvAjBmjvDxuhV/RtqZcPcI3lxvwOiC+SIeG41hC/buKq+fQ72yaHCGy17uwKTY8MG+blmB4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758186117; c=relaxed/simple; bh=jwRTUoN54HeyKKOV4Dj4gsSdmsvGsDnd8DlVRGDSbDU=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=unOPKE0FOUs3O1KRHCha4ReKxS2JJUcoxN+VpplYQwcthrQMYvPzW/59gJdDrjaWh9d84gkvcudS7sk99ZaqekI0P+VnWVYYSB1xDJz7fBTLQ5WRhmcZh3FKbGMOITOPs5eZnSeyUI6BI47GkpSz5PO0FZ8bKu164Hz2vkjYfZ0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GxoH68x7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GxoH68x7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D35ECC4CEF0; Thu, 18 Sep 2025 09:01:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758186117; bh=jwRTUoN54HeyKKOV4Dj4gsSdmsvGsDnd8DlVRGDSbDU=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=GxoH68x7hQHtLVtLVFaUYb+D7yUzMQAZLIcgN2NuzCvOueygHkFoCIZpYVskFiuxX y1TATBou4FNIrB9zORxwf1WlGgQDx1qcA8PYE7mHvTFGHzVCicFJUwRQ+a2yCVmcvO rM8g62VcDBWqaVYPddsMgb5LImWZa41OdSK5Y0rqFxnQ4DbfrQBkXJyQikO8/kUFEp J9nM5mVxOGfBgnoghgHUUQdEXBs7MIiePFYyp53CuZVYCSEiXXaGD3RoP+Ki8t2Psg bX/+R5//IRXVQRwAD9i/v2Uu9b2i7Usb6raiG+75yt5mpXFkU/ye8HASukUJ+zEtDf RPELvjxDeOA6g== From: Vincent Mailhol Date: Thu, 18 Sep 2025 18:00:27 +0900 Subject: [PATCH 4/4] can: mcba_usb: populate ndo_change_mtu() to prevent buffer overflow Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250918-can-fix-mtu-v1-4-0d1cada9393b@kernel.org> References: <20250918-can-fix-mtu-v1-0-0d1cada9393b@kernel.org> In-Reply-To: <20250918-can-fix-mtu-v1-0-0d1cada9393b@kernel.org> To: Marc Kleine-Budde , Oliver Hartkopp Cc: Arunachalam Santhanam , Akshay Bhat , Wolfgang Grandegger , Chen-Yu Tsai , Jernej Skrabec , Samuel Holland , Maxime Ripard , Gerhard Bertelsmann , Yasushi SHOJI , =?utf-8?q?Remigiusz_Ko=C5=82=C5=82=C4=85taj?= , linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev, Vincent Mailhol X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=2629; i=mailhol@kernel.org; h=from:subject:message-id; bh=jwRTUoN54HeyKKOV4Dj4gsSdmsvGsDnd8DlVRGDSbDU=; b=owGbwMvMwCV2McXO4Xp97WbG02pJDBmnT5Wa/3W9fdJ1Pmfsm6Utj1ZGxk9zsm+6r7lgB+Pcm 5eDojZs7ChlYRDjYpAVU2RZVs7JrdBR6B126K8lzBxWJpAhDFycAjAR0WaG/wW/Ql+G9f/64zBv YUxp32L9bP/UrZ+OrlxjbPWX05p91n1Ghmdnr4fNte61cj9dc6HiXP0mz5MHYxaub63d7v08Qvr yE0YA X-Developer-Key: i=mailhol@kernel.org; a=openpgp; fpr=ED8F700574E67F20E574E8E2AB5FEB886DBB99C2 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 =3D { .flags =3D 0xff, .len =3D 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 =3D 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 Anal= yzer") Signed-off-by: Vincent Mailhol --- 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 41c0a1c399bf36104fbf8991b537acdb01e7e950..1f9b915094e64de875adff35026= e9cd3beb0410d 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 =3D { .ndo_open =3D mcba_usb_open, .ndo_stop =3D mcba_usb_close, .ndo_start_xmit =3D mcba_usb_start_xmit, + .ndo_change_mtu =3D can_change_mtu, }; =20 static const struct ethtool_ops mcba_ethtool_ops =3D { --=20 2.49.1