From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1708C433E7 for ; Fri, 16 Oct 2020 17:21:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 35D3F20E65 for ; Fri, 16 Oct 2020 17:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390767AbgJPRV3 (ORCPT ); Fri, 16 Oct 2020 13:21:29 -0400 Received: from smtp09.smtpout.orange.fr ([80.12.242.131]:48659 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390454AbgJPRV3 (ORCPT ); Fri, 16 Oct 2020 13:21:29 -0400 Received: from tomoyo.flets-east.jp ([153.230.197.127]) by mwinf5d44 with ME id ghMB2300J2lQRaH03hML2a; Fri, 16 Oct 2020 19:21:26 +0200 X-ME-Helo: tomoyo.flets-east.jp X-ME-Auth: bWFpbGhvbC52aW5jZW50QHdhbmFkb28uZnI= X-ME-Date: Fri, 16 Oct 2020 19:21:26 +0200 X-ME-IP: 153.230.197.127 From: Vincent Mailhol To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-can@vger.kernel.org, Marc Kleine-Budde , Wolfgang Grandegger Cc: Arunachalam Santhanam , Vincent Mailhol , "David S. Miller" , Jakub Kicinski , Masahiro Yamada Subject: [PATCH v4 2/4] can: dev: add a helper function to get the correct length of Classical frames Date: Sat, 17 Oct 2020 02:20:23 +0900 Message-Id: <20201016172053.229281-1-mailhol.vincent@wanadoo.fr> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201016171402.229001-1-mailhol.vincent@wanadoo.fr> References: <20201016171402.229001-1-mailhol.vincent@wanadoo.fr> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org In classical CAN, the length of the data (i.e. CAN payload) is not always equal to the DLC! If the frame is a Remote Transmission Request (RTR), data length is always zero regardless of DLC value and else, if the DLC is greater than 8, the length is 8. Contrary to common belief, ISO 11898-1 Chapter 8.4.2.3 (DLC field) do allow DLCs greater than 8 for Classical Frames and specifies that those DLCs shall indicate that the data field is 8 bytes long. Above facts are widely unknown and so many developpers uses the "len" field of "struct canfd_frame" to get the length of classical CAN frames: this is incorrect! This patch introduces function get_can_len() which can be used in remediation. The function takes the SKB as an input in order to be able to determine if the frame is classical or FD. Signed-off-by: Vincent Mailhol --- Changes in v4: None Changes in v3: - Make get_can_len() return u8. - Make the skb const. Reference: https://lkml.org/lkml/2020/9/30/883 Changes in v2: None --- include/linux/can/dev.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h index 41ff31795320..d90890172d2a 100644 --- a/include/linux/can/dev.h +++ b/include/linux/can/dev.h @@ -192,6 +192,29 @@ u8 can_dlc2len(u8 can_dlc); /* map the sanitized data length to an appropriate data length code */ u8 can_len2dlc(u8 len); +/* + * get_can_len(skb) - get the length of the CAN payload. + * + * In classical CAN, the length of the data (i.e. CAN payload) is not + * always equal to the DLC! If the frame is a Remote Transmission + * Request (RTR), data length is always zero regardless of DLC value + * and else, if the DLC is greater than 8, the length is 8. Contrary + * to common belief, ISO 11898-1 Chapter 8.4.2.3 (DLC field) do allow + * DLCs greater than 8 for Classical Frames and specifies that those + * DLCs shall indicate that the data field is 8 bytes long. + */ +static inline u8 get_can_len(const struct sk_buff *skb) +{ + const struct canfd_frame *cf = (const struct canfd_frame *)skb->data; + + if (can_is_canfd_skb(skb)) + return min_t(u8, cf->len, CANFD_MAX_DLEN); + else if (cf->can_id & CAN_RTR_FLAG) + return 0; + else + return min_t(u8, cf->len, CAN_MAX_DLEN); +} + struct net_device *alloc_candev_mqs(int sizeof_priv, unsigned int echo_skb_max, unsigned int txqs, unsigned int rxqs); #define alloc_candev(sizeof_priv, echo_skb_max) \ -- 2.26.2