can: xilinx_can: xcan_write_frame(): fix use-after-free of transmitted SKB

can_put_echo_skb() takes ownership of the SKB and it may be freed
during or after the call.

However, xilinx_can xcan_write_frame() keeps using SKB after the call.

Fix that by only calling can_put_echo_skb() after the code is done
touching the SKB.

The tx_lock is held for the entire xcan_write_frame() execution and
also on the can_get_echo_skb() side so the order of operations does not
matter.

An earlier fix commit 3d3c817c3a40 ("can: xilinx_can: Fix usage of skb
memory") did not move the can_put_echo_skb() call far enough.

Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
Fixes: 1598efe57b3e ("can: xilinx_can: refactor code in preparation for CAN FD support")
Link: https://patch.msgid.link/20250822095002.168389-1-anssi.hannula@bitwise.fi
[mkl: add "commit" in front of sha1 in patch description]
[mkl: fix indention]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/xilinx_can.c b/drivers/net/can/xilinx_can.c
index 81baec8eb1e5dafb492e1464ea81f7fbc484cf64..a25a3ca62c12e3a0a5674581c3787595e543d843 100644 (file)
--- a/drivers/net/can/xilinx_can.c
+++ b/drivers/net/can/xilinx_can.c
@@ -690,14 +690,6 @@ static void xcan_write_frame(struct net_device *ndev, struct sk_buff *skb,
                dlc |= XCAN_DLCR_EDL_MASK;
        }
 
-       if (!(priv->devtype.flags & XCAN_FLAG_TX_MAILBOXES) &&
-           (priv->devtype.flags & XCAN_FLAG_TXFEMP))
-               can_put_echo_skb(skb, ndev, priv->tx_head % priv->tx_max, 0);
-       else
-               can_put_echo_skb(skb, ndev, 0, 0);
-
-       priv->tx_head++;
-
        priv->write_reg(priv, XCAN_FRAME_ID_OFFSET(frame_offset), id);
        /* If the CAN frame is RTR frame this write triggers transmission
         * (not on CAN FD)
@@ -730,6 +722,14 @@ static void xcan_write_frame(struct net_device *ndev, struct sk_buff *skb,
                                        data[1]);
                }
        }
+
+       if (!(priv->devtype.flags & XCAN_FLAG_TX_MAILBOXES) &&
+           (priv->devtype.flags & XCAN_FLAG_TXFEMP))
+               can_put_echo_skb(skb, ndev, priv->tx_head % priv->tx_max, 0);
+       else
+               can_put_echo_skb(skb, ndev, 0, 0);
+
+       priv->tx_head++;
 }
 
 /**