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    Subject[PATCH 4.9 145/223] netrom: hold sock when setting skb->destructor
    Date
    From: Cong Wang <xiyou.wangcong@gmail.com>

    [ Upstream commit 4638faac032756f7eab5524be7be56bee77e426b ]

    sock_efree() releases the sock refcnt, if we don't hold this refcnt
    when setting skb->destructor to it, the refcnt would not be balanced.
    This leads to several bug reports from syzbot.

    I have checked other users of sock_efree(), all of them hold the
    sock refcnt.

    Fixes: c8c8218ec5af ("netrom: fix a memory leak in nr_rx_frame()")
    Reported-and-tested-by: <syzbot+622bdabb128acc33427d@syzkaller.appspotmail.com>
    Reported-and-tested-by: <syzbot+6eaef7158b19e3fec3a0@syzkaller.appspotmail.com>
    Reported-and-tested-by: <syzbot+9399c158fcc09b21d0d2@syzkaller.appspotmail.com>
    Reported-and-tested-by: <syzbot+a34e5f3d0300163f0c87@syzkaller.appspotmail.com>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/netrom/af_netrom.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/net/netrom/af_netrom.c
    +++ b/net/netrom/af_netrom.c
    @@ -968,6 +968,7 @@ int nr_rx_frame(struct sk_buff *skb, str

    window = skb->data[20];

    + sock_hold(make);
    skb->sk = make;
    skb->destructor = sock_efree;
    make->sk_state = TCP_ESTABLISHED;

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