From patchwork Sat Sep 26 17:57:52 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent MAILHOL X-Patchwork-Id: 260120 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=-12.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 526A0C4727F for ; Sat, 26 Sep 2020 17:59:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1DBE5206FC for ; Sat, 26 Sep 2020 17:59:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730070AbgIZR7W (ORCPT ); Sat, 26 Sep 2020 13:59:22 -0400 Received: from smtp11.smtpout.orange.fr ([80.12.242.133]:32823 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726210AbgIZR7V (ORCPT ); Sat, 26 Sep 2020 13:59:21 -0400 Received: from tomoyo.flets-east.jp ([153.230.197.127]) by mwinf5d89 with ME id YhyX2300D2lQRaH03hzH1w; Sat, 26 Sep 2020 19:59:20 +0200 X-ME-Helo: tomoyo.flets-east.jp X-ME-Auth: bWFpbGhvbC52aW5jZW50QHdhbmFkb28uZnI= X-ME-Date: Sat, 26 Sep 2020 19:59:20 +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, Wolfgang Grandegger , Marc Kleine-Budde , "David S . Miller" Cc: Vincent Mailhol Subject: [PATCH 2/6] can: dev: add a helper function to get the correct length of Classical frames Date: Sun, 27 Sep 2020 02:57:52 +0900 Message-Id: <20200926175810.278529-3-mailhol.vincent@wanadoo.fr> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200926175810.278529-1-mailhol.vincent@wanadoo.fr> References: <20200926175810.278529-1-mailhol.vincent@wanadoo.fr> MIME-Version: 1.0 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 --- 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 5e3d45525bd3..72a8a60c0094 100644 --- a/include/linux/can/dev.h +++ b/include/linux/can/dev.h @@ -177,6 +177,29 @@ 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 int get_can_len(struct sk_buff *skb) +{ + struct canfd_frame *cf = (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) \