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    Subject[PATCH v3] set fake_rtable's dst to NULL to avoid kernel Oops.
    When bridge is deleted before tap/vif device's delete, kernel may 
    encounter an oops because of NULL reference to fake_rtable's dst.
    Set fake_rtable's dst to NULL before sending packets out can solve this
    problem.

    v3 enrich commit header

    v2 added a new flag DST_FAKE_RTABLE to dst_entry struct.


    Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: Peter Huang <peter.huangpeng@huawei.com>
    ---
    include/linux/netfilter_bridge.h | 8 ++++++++
    include/net/dst.h | 1 +
    net/bridge/br_forward.c | 1 +
    net/bridge/br_netfilter.c | 8 ++------
    4 files changed, 12 insertions(+), 6 deletions(-)
    diff --git a/include/linux/netfilter_bridge.h
    b/include/linux/netfilter_bridge.h
    index 0ddd161..51745df 100644
    --- a/include/linux/netfilter_bridge.h
    +++ b/include/linux/netfilter_bridge.h
    @@ -104,9 +104,17 @@ struct bridge_skb_cb {
    } daddr;
    };

    +static inline void br_drop_fake_rtable(struct sk_buff *skb) {
    + struct dst_entry *dst = skb_dst(skb);
    +
    + if (dst && (dst->flags & DST_FAKE_RTABLE))
    + skb_dst_drop(skb);
    +}
    +
    #else
    #define nf_bridge_maybe_copy_header(skb) (0)
    #define nf_bridge_pad(skb) (0)
    +#define br_drop_fake_rtable(skb) (0)
    #endif /* CONFIG_BRIDGE_NETFILTER */

    #endif /* __KERNEL__ */
    diff --git a/include/net/dst.h b/include/net/dst.h
    index 59c5d18..b094030 100644
    --- a/include/net/dst.h
    +++ b/include/net/dst.h
    @@ -55,6 +55,7 @@ struct dst_entry {
    #define DST_NOCACHE 0x0010
    #define DST_NOCOUNT 0x0020
    #define DST_NOPEER 0x0040
    +#define DST_FAKE_RTABLE 0x0080

    short error;
    short obsolete;
    diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
    index 61f6534..a2098e3 100644
    --- a/net/bridge/br_forward.c
    +++ b/net/bridge/br_forward.c
    @@ -47,6 +47,7 @@ int br_dev_queue_push_xmit(struct sk_buff *skb)
    kfree_skb(skb);
    } else {
    skb_push(skb, ETH_HLEN);
    + br_drop_fake_rtable(skb);
    dev_queue_xmit(skb);
    }

    diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
    index dec4f38..d7f49b6 100644
    --- a/net/bridge/br_netfilter.c
    +++ b/net/bridge/br_netfilter.c
    @@ -156,7 +156,7 @@ void br_netfilter_rtable_init(struct net_bridge *br)
    rt->dst.dev = br->dev;
    rt->dst.path = &rt->dst;
    dst_init_metrics(&rt->dst, br_dst_default_metrics, true);
    - rt->dst.flags = DST_NOXFRM | DST_NOPEER;
    + rt->dst.flags = DST_NOXFRM | DST_NOPEER | DST_FAKE_RTABLE;
    rt->dst.ops = &fake_dst_ops;
    }

    @@ -694,11 +694,7 @@ static unsigned int br_nf_local_in(unsigned int
    hook, struct sk_buff *skb,
    const struct net_device *out,
    int (*okfn)(struct sk_buff *))
    {
    - struct rtable *rt = skb_rtable(skb);
    -
    - if (rt && rt == bridge_parent_rtable(in))
    - skb_dst_drop(skb);
    -
    + br_drop_fake_rtable(skb);
    return NF_ACCEPT;
    }

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