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    Subject[PATCH 4.19 36/77] net-sysfs: take the rtnl lock when storing xps_rxqs
    Date
    From: Antoine Tenart <atenart@kernel.org>

    [ Upstream commit 2d57b4f142e0b03e854612b8e28978935414bced ]

    Two race conditions can be triggered when storing xps rxqs, resulting in
    various oops and invalid memory accesses:

    1. Calling netdev_set_num_tc while netif_set_xps_queue:

    - netif_set_xps_queue uses dev->tc_num as one of the parameters to
    compute the size of new_dev_maps when allocating it. dev->tc_num is
    also used to access the map, and the compiler may generate code to
    retrieve this field multiple times in the function.

    - netdev_set_num_tc sets dev->tc_num.

    If new_dev_maps is allocated using dev->tc_num and then dev->tc_num
    is set to a higher value through netdev_set_num_tc, later accesses to
    new_dev_maps in netif_set_xps_queue could lead to accessing memory
    outside of new_dev_maps; triggering an oops.

    2. Calling netif_set_xps_queue while netdev_set_num_tc is running:

    2.1. netdev_set_num_tc starts by resetting the xps queues,
    dev->tc_num isn't updated yet.

    2.2. netif_set_xps_queue is called, setting up the map with the
    *old* dev->num_tc.

    2.3. netdev_set_num_tc updates dev->tc_num.

    2.4. Later accesses to the map lead to out of bound accesses and
    oops.

    A similar issue can be found with netdev_reset_tc.

    One way of triggering this is to set an iface up (for which the driver
    uses netdev_set_num_tc in the open path, such as bnx2x) and writing to
    xps_rxqs in a concurrent thread. With the right timing an oops is
    triggered.

    Both issues have the same fix: netif_set_xps_queue, netdev_set_num_tc
    and netdev_reset_tc should be mutually exclusive. We do that by taking
    the rtnl lock in xps_rxqs_store.

    Fixes: 8af2c06ff4b1 ("net-sysfs: Add interface for Rx queue(s) map per Tx queue")
    Signed-off-by: Antoine Tenart <atenart@kernel.org>
    Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/core/net-sysfs.c | 7 +++++++
    1 file changed, 7 insertions(+)

    --- a/net/core/net-sysfs.c
    +++ b/net/core/net-sysfs.c
    @@ -1428,10 +1428,17 @@ static ssize_t xps_rxqs_store(struct net
    return err;
    }

    + if (!rtnl_trylock()) {
    + bitmap_free(mask);
    + return restart_syscall();
    + }
    +
    cpus_read_lock();
    err = __netif_set_xps_queue(dev, mask, index, true);
    cpus_read_unlock();

    + rtnl_unlock();
    +
    kfree(mask);
    return err ? : len;
    }

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