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    Subject[PATCH 3.18 11/31] can: dev: __can_get_echo_skb(): fix bogous check for non-existing skb by removing it
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>

    commit 7b12c8189a3dc50638e7d53714c88007268d47ef upstream.

    This patch revert commit 7da11ba5c506
    ("can: dev: __can_get_echo_skb(): print error message, if trying to echo non existing skb")

    After introduction of this change we encountered following new error
    message on various i.MX plattforms (flexcan):

    | flexcan 53fc8000.can can0: __can_get_echo_skb: BUG! Trying to echo non
    | existing skb: can_priv::echo_skb[0]

    The introduction of the message was a mistake because
    priv->echo_skb[idx] = NULL is a perfectly valid in following case: If
    CAN_RAW_LOOPBACK is disabled (setsockopt) in applications, the pkt_type
    of the tx skb's given to can_put_echo_skb is set to PACKET_LOOPBACK. In
    this case can_put_echo_skb will not set priv->echo_skb[idx]. It is
    therefore kept NULL.

    As additional argument for revert: The order of check and usage of idx
    was changed. idx is used to access an array element before checking it's
    boundaries.

    Signed-off-by: Manfred Schlaegl <manfred.schlaegl@ginzinger.com>
    Fixes: 7da11ba5c506 ("can: dev: __can_get_echo_skb(): print error message, if trying to echo non existing skb")
    Cc: linux-stable <stable@vger.kernel.org>
    Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/net/can/dev.c | 27 +++++++++++++--------------
    1 file changed, 13 insertions(+), 14 deletions(-)

    --- a/drivers/net/can/dev.c
    +++ b/drivers/net/can/dev.c
    @@ -346,8 +346,6 @@ EXPORT_SYMBOL_GPL(can_put_echo_skb);
    struct sk_buff *__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
    {
    struct can_priv *priv = netdev_priv(dev);
    - struct sk_buff *skb = priv->echo_skb[idx];
    - struct canfd_frame *cf;

    if (idx >= priv->echo_skb_max) {
    netdev_err(dev, "%s: BUG! Trying to access can_priv::echo_skb out of bounds (%u/max %u)\n",
    @@ -355,20 +353,21 @@ struct sk_buff *__can_get_echo_skb(struc
    return NULL;
    }

    - if (!skb) {
    - netdev_err(dev, "%s: BUG! Trying to echo non existing skb: can_priv::echo_skb[%u]\n",
    - __func__, idx);
    - return NULL;
    - }
    + if (priv->echo_skb[idx]) {
    + /* Using "struct canfd_frame::len" for the frame
    + * length is supported on both CAN and CANFD frames.
    + */
    + struct sk_buff *skb = priv->echo_skb[idx];
    + struct canfd_frame *cf = (struct canfd_frame *)skb->data;
    + u8 len = cf->len;

    - /* Using "struct canfd_frame::len" for the frame
    - * length is supported on both CAN and CANFD frames.
    - */
    - cf = (struct canfd_frame *)skb->data;
    - *len_ptr = cf->len;
    - priv->echo_skb[idx] = NULL;
    + *len_ptr = len;
    + priv->echo_skb[idx] = NULL;
    +
    + return skb;
    + }

    - return skb;
    + return NULL;
    }

    /*

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