[PATCH net] net: ethernet: mtk_ppe: avoid NULL deref when gmac0 is disabled

[Sven Eckelmann (Plasma Cloud)]

If the gmac0 is disabled, the precheck for a valid ingress device will
cause a NULL pointer deref and crash the system. This happens because
eth->netdev[0] will be NULL but the code will directly try to access
netdev_ops.

Instead of just checking for the first net_device, it must be checked if
any of the mtk_eth net_devices is matching the netdev_ops of the ingress
device.

Cc: stable at vger.kernel.org
Fixes: 73cfd947dbdb ("net: ethernet: mtk_eth_soc: ppe: prevent ppe update for non-mtk devices")
Signed-off-by: Sven Eckelmann (Plasma Cloud) <se at simonwunderlich.de>
---
 drivers/net/ethernet/mediatek/mtk_ppe_offload.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
index cb30108f2bf6..cc8c4ef8038f 100644
--- a/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
+++ b/drivers/net/ethernet/mediatek/mtk_ppe_offload.c
@@ -244,6 +244,25 @@ mtk_flow_set_output_device(struct mtk_eth *eth, struct mtk_foe_entry *foe,
 	return 0;
 }
 
+static bool
+mtk_flow_is_valid_idev(const struct mtk_eth *eth, const struct net_device *idev)
+{
+	size_t i;
+
+	if (!idev)
+		return false;
+
+	for (i = 0; i < ARRAY_SIZE(eth->netdev); i++) {
+		if (!eth->netdev[i])
+			continue;
+
+		if (idev->netdev_ops == eth->netdev[i]->netdev_ops)
+			return true;
+	}
+
+	return false;
+}
+
 static int
 mtk_flow_offload_replace(struct mtk_eth *eth, struct flow_cls_offload *f,
 			 int ppe_index)
@@ -270,7 +289,7 @@ mtk_flow_offload_replace(struct mtk_eth *eth, struct flow_cls_offload *f,
 		flow_rule_match_meta(rule, &match);
 		if (mtk_is_netsys_v2_or_greater(eth)) {
 			idev = __dev_get_by_index(&init_net, match.key->ingress_ifindex);
-			if (idev && idev->netdev_ops == eth->netdev[0]->netdev_ops) {
+			if (mtk_flow_is_valid_idev(eth, idev)) {
 				struct mtk_mac *mac = netdev_priv(idev);
 
 				if (WARN_ON(mac->ppe_idx >= eth->soc->ppe_num))

---
base-commit: 70b439bf06f6a12e491f827fa81a9887a11501f9
change-id: 20260324-wed-crash-gmac0-disabled-ae3a551cb154

Best regards,
--  
Sven Eckelmann (Plasma Cloud) <se at simonwunderlich.de>