4.9-stable review patch.  If anyone has any objections, please let me know.


From: Florian Fainelli <f.faine...@gmail.com>

[ Upstream commit faf3a932fbeb77860226a8323eacb835edc98648 ]

It is perfectly possible to have non zero indexed switches being present
in a DSA switch tree, in such a case, we will be deferencing a NULL
pointer while dsa_cpu_port_ethtool_{setup,restore}. Be more defensive
and ensure that dst->ds[0] is valid before doing anything with it.

Fixes: 0c73c523cf73 ("net: dsa: Initialize CPU port ethtool ops per tree")
Signed-off-by: Florian Fainelli <f.faine...@gmail.com>
Reviewed-by: Vivien Didelot <vivien.dide...@savoirfairelinux.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
 net/dsa/dsa2.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -394,9 +394,11 @@ static int dsa_dst_apply(struct dsa_swit
                        return err;
-       err = dsa_cpu_port_ethtool_setup(dst->ds[0]);
-       if (err)
-               return err;
+       if (dst->ds[0]) {
+               err = dsa_cpu_port_ethtool_setup(dst->ds[0]);
+               if (err)
+                       return err;
+       }
        /* If we use a tagging format that doesn't have an ethertype
         * field, make sure that all packets from this point on get
@@ -433,7 +435,8 @@ static void dsa_dst_unapply(struct dsa_s
                dsa_ds_unapply(dst, ds);
-       dsa_cpu_port_ethtool_restore(dst->ds[0]);
+       if (dst->ds[0])
+               dsa_cpu_port_ethtool_restore(dst->ds[0]);
        pr_info("DSA: tree %d unapplied\n", dst->tree);
        dst->applied = false;

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