Advisory [CVE-2026-53247] Fix use-after-free in metadata dst teardown

In the Linux kernel, the following vulnerability has been resolved: net: ethernet: mtk_eth_soc: Fix use-after-free in metadata dst teardown mtk_free_dev() calls metadata_dst_free() which frees the metadata_dst with kfree() immediately, bypassing the RCU grace period.

In the RX path, skb_dst_set_noref() sets a non-refcounted pointer from the skb to the metadata_dst. This function requires RCU read-side protection and the dst must remain valid until all RCU readers complete.

Since metadata_dst_free() calls kfree() directly, a use-after-free can occur if any skb still holds a noref pointer to the dst when the driver tears it down.

Replace metadata_dst_free() with dst_release() which properly goes through the refcount path: when the refcount drops to zero, it schedules the actual free via call_rcu_hurry(), ensuring all RCU readers have completed before the memory is freed. A flaw was found in the Linux kernel's ethernet driver for MediaTek (mtk_eth_soc) network devices.

This vulnerability, a 'use-after-free', occurs when the system attempts to free a memory region while it is still being used by network packet processing. This can allow a local attacker to trigger system instability, potentially leading to a denial of service (DoS) or, in some cases, unauthorized code execution.

Red Hat severity: not rated. Weakness: CWE-825.