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    Subject[PATCH 3.16 001/202] batman-adv: Avoid WARN on net_device without parent in netns
    3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Sven Eckelmann <sven@narfation.org>

    commit 955d3411a17f590364238bd0d3329b61f20c1cd2 upstream.

    It is not allowed to use WARN* helpers on potential incorrect input from
    the user or transient problems because systems configured as panic_on_warn
    will reboot due to such a problem.

    A NULL return value of __dev_get_by_index can be caused by various problems
    which can either be related to the system configuration or problems
    (incorrectly returned network namespaces) in other (virtual) net_device
    drivers. batman-adv should not cause a (harmful) WARN in this situation and
    instead only report it via a simple message.

    Fixes: b7eddd0b3950 ("batman-adv: prevent using any virtual device created on batman-adv as hard-interface")
    Reported-by: syzbot+c764de0fcfadca9a8595@syzkaller.appspotmail.com
    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    Signed-off-by: Sven Eckelmann <sven@narfation.org>
    Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/net/batman-adv/hard-interface.c
    +++ b/net/batman-adv/hard-interface.c
    @@ -89,8 +89,10 @@ static bool batadv_is_on_batman_iface(co
    /* recurse over the parent device */
    parent_dev = __dev_get_by_index(&init_net, net_dev->iflink);
    /* if we got a NULL parent_dev there is something broken.. */
    - if (WARN(!parent_dev, "Cannot find parent device"))
    + if (!parent_dev) {
    + pr_err("Cannot find parent device\n");
    return false;
    + }

    ret = batadv_is_on_batman_iface(parent_dev);

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