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    Subject[PATCH 4.8 15/45] net: dsa: fix unbalanced dsa_switch_tree reference counting
    Date
    4.8-stable review patch.  If anyone has any objections, please let me know.

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

    From: Nikita Yushchenko <nikita.yoush@cogentembedded.com>


    [ Upstream commit 7a99cd6e213685b78118382e6a8fed506c82ccb2 ]

    _dsa_register_switch() gets a dsa_switch_tree object either via
    dsa_get_dst() or via dsa_add_dst(). Former path does not increase kref
    in returned object (resulting into caller not owning a reference),
    while later path does create a new object (resulting into caller owning
    a reference).

    The rest of _dsa_register_switch() assumes that it owns a reference, and
    calls dsa_put_dst().

    This causes a memory breakage if first switch in the tree initialized
    successfully, but second failed to initialize. In particular, freed
    dsa_swith_tree object is left referenced by switch that was initialized,
    and later access to sysfs attributes of that switch cause OOPS.

    To fix, need to add kref_get() call to dsa_get_dst().

    Fixes: 83c0afaec7b7 ("net: dsa: Add new binding implementation")
    Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
    Reviewed-by: Andrew Lunn <andrew@lunn.ch>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/dsa/dsa2.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/net/dsa/dsa2.c
    +++ b/net/dsa/dsa2.c
    @@ -28,8 +28,10 @@ static struct dsa_switch_tree *dsa_get_d
    struct dsa_switch_tree *dst;

    list_for_each_entry(dst, &dsa_switch_trees, list)
    - if (dst->tree == tree)
    + if (dst->tree == tree) {
    + kref_get(&dst->refcount);
    return dst;
    + }
    return NULL;
    }


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