net: mediatek: Fix potential NULL pointer dereference in dummy net_device handling

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: mediatek: Fix potential NULL pointer dereference in dummy net_device handling Move the freeing of the dummy net_device from mtk_free_dev() to mtk_remove(). Previously, if alloc_netdev_dummy() failed in mtk_probe(), eth->dummy_dev would be NULL. The error path would then call mtk_free_dev(), which in turn called free_netdev() assuming dummy_dev was allocated (but it was not), potentially causing a NULL pointer dereference. By moving free_netdev() to mtk_remove(), we ensure it's only called when mtk_probe() has succeeded and dummy_dev is fully allocated. This addresses a potential NULL pointer dereference detected by Smatch[1].

References

• https://git.kernel.org/stable/c/af6bd5c9901b13a26eaf4d57d97a813297791596
• https://git.kernel.org/stable/c/16f3a28cf5f876a7f3550d8f4c870a7b41bcfaef