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    Subject[PATCH 3.16 227/410] bridge: check brport attr show in brport_show
    3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Xin Long <lucien.xin@gmail.com>

    commit 1b12580af1d0677c3c3a19e35bfe5d59b03f737f upstream.

    Now br_sysfs_if file flush doesn't have attr show. To read it will
    cause kernel panic after users chmod u+r this file.

    Xiong found this issue when running the commands:

    ip link add br0 type bridge
    ip link add type veth
    ip link set veth0 master br0
    chmod u+r /sys/devices/virtual/net/veth0/brport/flush
    timeout 3 cat /sys/devices/virtual/net/veth0/brport/flush

    kernel crashed with NULL a pointer dereference call trace.

    This patch is to fix it by return -EINVAL when brport_attr->show
    is null, just the same as the check for brport_attr->store in
    brport_store().

    Fixes: 9cf637473c85 ("bridge: add sysfs hook to flush forwarding table")
    Reported-by: Xiong Zhou <xzhou@redhat.com>
    Signed-off-by: Xin Long <lucien.xin@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    net/bridge/br_sysfs_if.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/net/bridge/br_sysfs_if.c
    +++ b/net/bridge/br_sysfs_if.c
    @@ -225,6 +225,9 @@ static ssize_t brport_show(struct kobjec
    struct brport_attribute *brport_attr = to_brport_attr(attr);
    struct net_bridge_port *p = to_brport(kobj);

    + if (!brport_attr->show)
    + return -EINVAL;
    +
    return brport_attr->show(p, buf);
    }

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