linux-kernel - [PATCH v5 3/5] can: do not copy the payload of RTR frames

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Message-Id: <20211207121531.42941-4-mailhol.vincent@wanadoo.fr>
Date:   Tue,  7 Dec 2021 21:15:29 +0900
From:   Vincent Mailhol <mailhol.vincent@...adoo.fr>
To:     Marc Kleine-Budde <mkl@...gutronix.de>, linux-can@...r.kernel.org
Cc:     Oliver Hartkopp <socketcan@...tkopp.net>,
        Jimmy Assarsson <extja@...ser.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Yasushi SHOJI <yashi@...cecubics.com>
Subject: [PATCH v5 3/5] can: do not copy the payload of RTR frames

The actual payload length of the CAN Remote Transmission Request (RTR)
frames is always 0, i.e. nothing is transmitted on the wire. However,
those RTR frames still use the DLC to indicate the length of the
requested frame.

For this reason, it is incorrect to copy the payload of RTR frames
(the payload buffer would only contain garbage data). This patch
encapsulates the payload copy in a check toward the RTR flag.

CC: Yasushi SHOJI <yashi@...cecubics.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
---
 drivers/net/can/pch_can.c      | 15 ++++++++-------
 drivers/net/can/spi/mcp251x.c  |  3 ++-
 drivers/net/can/usb/mcba_usb.c |  8 ++++----
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/net/can/pch_can.c b/drivers/net/can/pch_can.c
index 6b45840db1f9..4bf9bfc4de72 100644
--- a/drivers/net/can/pch_can.c
+++ b/drivers/net/can/pch_can.c
@@ -677,16 +677,17 @@ static int pch_can_rx_normal(struct net_device *ndev, u32 obj_num, int quota)
 			cf->can_id = id;
 		}
 
-		if (id2 & PCH_ID2_DIR)
-			cf->can_id |= CAN_RTR_FLAG;
-
 		cf->len = can_cc_dlc2len((ioread32(&priv->regs->
 						    ifregs[0].mcont)) & 0xF);
 
-		for (i = 0; i < cf->len; i += 2) {
-			data_reg = ioread16(&priv->regs->ifregs[0].data[i / 2]);
-			cf->data[i] = data_reg;
-			cf->data[i + 1] = data_reg >> 8;
+		if (id2 & PCH_ID2_DIR) {
+			cf->can_id |= CAN_RTR_FLAG;
+		} else {
+			for (i = 0; i < cf->len; i += 2) {
+				data_reg = ioread16(&priv->regs->ifregs[0].data[i / 2]);
+				cf->data[i] = data_reg;
+				cf->data[i + 1] = data_reg >> 8;
+			}
 		}
 
 		rcv_pkts++;
diff --git a/drivers/net/can/spi/mcp251x.c b/drivers/net/can/spi/mcp251x.c
index 0579ab74f728..db3fa98569c4 100644
--- a/drivers/net/can/spi/mcp251x.c
+++ b/drivers/net/can/spi/mcp251x.c
@@ -733,7 +733,8 @@ static void mcp251x_hw_rx(struct spi_device *spi, int buf_idx)
 	}
 	/* Data length */
 	frame->len = can_cc_dlc2len(buf[RXBDLC_OFF] & RXBDLC_LEN_MASK);
-	memcpy(frame->data, buf + RXBDAT_OFF, frame->len);
+	if (!(frame->can_id & CAN_RTR_FLAG))
+		memcpy(frame->data, buf + RXBDAT_OFF, frame->len);
 
 	priv->net->stats.rx_packets++;
 	priv->net->stats.rx_bytes += frame->len;
diff --git a/drivers/net/can/usb/mcba_usb.c b/drivers/net/can/usb/mcba_usb.c
index a1a154c08b7f..162d2e11cadd 100644
--- a/drivers/net/can/usb/mcba_usb.c
+++ b/drivers/net/can/usb/mcba_usb.c
@@ -450,12 +450,12 @@ static void mcba_usb_process_can(struct mcba_priv *priv,
 		cf->can_id = (sid & 0xffe0) >> 5;
 	}
 
-	if (msg->dlc & MCBA_DLC_RTR_MASK)
-		cf->can_id |= CAN_RTR_FLAG;
-
 	cf->len = can_cc_dlc2len(msg->dlc & MCBA_DLC_MASK);
 
-	memcpy(cf->data, msg->data, cf->len);
+	if (msg->dlc & MCBA_DLC_RTR_MASK)
+		cf->can_id |= CAN_RTR_FLAG;
+	else
+		memcpy(cf->data, msg->data, cf->len);
 
 	stats->rx_packets++;
 	stats->rx_bytes += cf->len;
-- 
2.32.0