[PATCH net 2/2] net: ethernet: mtk_eth_soc: Fix use-after-free in metadata dst teardown

[Lorenzo Bianconi]

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.

Fixes: 2d7605a72906 ("net: ethernet: mtk_eth_soc: enable hardware DSA untagging")
Signed-off-by: Lorenzo Bianconi <lorenzo at kernel.org>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 8d225bc9f063..7d771168b990 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -4491,7 +4491,7 @@ static int mtk_free_dev(struct mtk_eth *eth)
 	for (i = 0; i < ARRAY_SIZE(eth->dsa_meta); i++) {
 		if (!eth->dsa_meta[i])
 			break;
-		metadata_dst_free(eth->dsa_meta[i]);
+		dst_release(&eth->dsa_meta[i]->dst);
 	}
 
 	return 0;

-- 
2.54.0