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From:   Hangyu Hua <hbh25y@gmail.com>
To:     rcsekar@samsung.com, wg@grandegger.com, mkl@pengutronix.de,
        davem@davemloft.net, kuba@kernel.org
Cc:     linux-can@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Hangyu Hua <hbh25y@gmail.com>
Subject: [PATCH] can: m_can: fix a possible use after free in m_can_tx_handler()
Date:   Thu, 17 Mar 2022 11:01:43 +0800
Message-Id: <20220317030143.14668-1-hbh25y@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

can_put_echo_skb will clone skb then free the skb. It is better to avoid using
skb after can_put_echo_skb.

Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
---
 drivers/net/can/m_can/m_can.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 1a4b56f6fa8c..98be5742f4f5 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -1607,6 +1607,7 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 	u32 cccr, fdflags;
 	int err;
 	int putidx;
+	unsigned int len = skb->len;
 
 	cdev->tx_skb = NULL;
 
@@ -1642,7 +1643,7 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 		if (cdev->can.ctrlmode & CAN_CTRLMODE_FD) {
 			cccr = m_can_read(cdev, M_CAN_CCCR);
 			cccr &= ~CCCR_CMR_MASK;
-			if (can_is_canfd_skb(skb)) {
+			if (len == CANFD_MTU) {
 				if (cf->flags & CANFD_BRS)
 					cccr |= FIELD_PREP(CCCR_CMR_MASK,
 							   CCCR_CMR_CANFD_BRS);
-- 
2.25.1