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    Subject[PATCH 4.9 36/66] net: lan78xx: Fix race in tx pending skb size calculation
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: Stefan Wahren <stefan.wahren@i2se.com>

    commit dea39aca1d7aef1e2b95b07edeacf04cc8863a2e upstream.

    The skb size calculation in lan78xx_tx_bh is in race with the start_xmit,
    which could lead to rare kernel oopses. So protect the whole skb walk with
    a spin lock. As a benefit we can unlink the skb directly.

    This patch was tested on Raspberry Pi 3B+

    Link: https://github.com/raspberrypi/linux/issues/2608
    Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet")
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
    Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/net/usb/lan78xx.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/drivers/net/usb/lan78xx.c
    +++ b/drivers/net/usb/lan78xx.c
    @@ -2964,6 +2964,7 @@ static void lan78xx_tx_bh(struct lan78xx
    pkt_cnt = 0;
    count = 0;
    length = 0;
    + spin_lock_irqsave(&tqp->lock, flags);
    for (skb = tqp->next; pkt_cnt < tqp->qlen; skb = skb->next) {
    if (skb_is_gso(skb)) {
    if (pkt_cnt) {
    @@ -2972,7 +2973,8 @@ static void lan78xx_tx_bh(struct lan78xx
    }
    count = 1;
    length = skb->len - TX_OVERHEAD;
    - skb2 = skb_dequeue(tqp);
    + __skb_unlink(skb, tqp);
    + spin_unlock_irqrestore(&tqp->lock, flags);
    goto gso_skb;
    }

    @@ -2981,6 +2983,7 @@ static void lan78xx_tx_bh(struct lan78xx
    skb_totallen = skb->len + roundup(skb_totallen, sizeof(u32));
    pkt_cnt++;
    }
    + spin_unlock_irqrestore(&tqp->lock, flags);

    /* copy to a single skb */
    skb = alloc_skb(skb_totallen, GFP_ATOMIC);

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