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    Subject[PATCH 4.14 03/78] hamradio: remove needs_free_netdev to avoid UAF
    Date
    From: Lin Ma <linma@zju.edu.cn>

    commit 81b1d548d00bcd028303c4f3150fa753b9b8aa71 upstream.

    The former patch "defer 6pack kfree after unregister_netdev" reorders
    the kfree of two buffer after the unregister_netdev to prevent the race
    condition. It also adds free_netdev() function in sixpack_close(), which
    is a direct copy from the similar code in mkiss_close().

    However, in sixpack driver, the flag needs_free_netdev is set to true in
    sp_setup(), hence the unregister_netdev() will free the netdev
    automatically. Therefore, as the sp is netdev_priv, use-after-free
    occurs.

    This patch removes the needs_free_netdev = true and just let the
    free_netdev to finish this deallocation task.

    Fixes: 0b9111922b1f ("hamradio: defer 6pack kfree after unregister_netdev")
    Signed-off-by: Lin Ma <linma@zju.edu.cn>
    Link: https://lore.kernel.org/r/20211111141402.7551-1-linma@zju.edu.cn
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/hamradio/6pack.c | 1 -
    1 file changed, 1 deletion(-)

    --- a/drivers/net/hamradio/6pack.c
    +++ b/drivers/net/hamradio/6pack.c
    @@ -311,7 +311,6 @@ static void sp_setup(struct net_device *
    {
    /* Finish setting up the DEVICE info. */
    dev->netdev_ops = &sp_netdev_ops;
    - dev->needs_free_netdev = true;
    dev->mtu = SIXP_MTU;
    dev->hard_header_len = AX25_MAX_HEADER_LEN;
    dev->header_ops = &ax25_header_ops;

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