[PATCH net] net: dsa: don't assign an error value to tag_ops

[George McCollister]

Use a temporary variable to hold the return value from
dsa_tag_driver_get() instead of assigning it to dst->tag_ops. Leaving
an error value in dst->tag_ops can result in deferencing an invalid
pointer when a deferred switch configuration happens later.

Fixes: 357f203bb3b5 ("net: dsa: keep a copy of the tagging protocol in the DSA 
switch tree")

Signed-off-by: George McCollister <george.mccollis...@gmail.com>
---
 net/dsa/dsa2.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index eb709d988c54..8f9e35e1aa89 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -1068,6 +1068,7 @@ static int dsa_port_parse_cpu(struct dsa_port *dp, struct 
net_device *master)
 {
        struct dsa_switch *ds = dp->ds;
        struct dsa_switch_tree *dst = ds->dst;
+       const struct dsa_device_ops *tag_ops;
        enum dsa_tag_protocol tag_protocol;
 
        tag_protocol = dsa_get_tag_protocol(dp, master);
@@ -1082,14 +1083,16 @@ static int dsa_port_parse_cpu(struct dsa_port *dp, 
struct net_device *master)
                 * nothing to do here.
                 */
        } else {
-               dst->tag_ops = dsa_tag_driver_get(tag_protocol);
-               if (IS_ERR(dst->tag_ops)) {
-                       if (PTR_ERR(dst->tag_ops) == -ENOPROTOOPT)
+               tag_ops = dsa_tag_driver_get(tag_protocol);
+               if (IS_ERR(tag_ops)) {
+                       if (PTR_ERR(tag_ops) == -ENOPROTOOPT)
                                return -EPROBE_DEFER;
                        dev_warn(ds->dev, "No tagger for this switch\n");
                        dp->master = NULL;
-                       return PTR_ERR(dst->tag_ops);
+                       return PTR_ERR(tag_ops);
                }
+
+               dst->tag_ops = tag_ops;
        }
 
        dp->master = master;
-- 
2.11.0