[PATCH net-next v8 4/5] net: stmmac: fix VLAN tag stripping on non-linear RX frames

[Lorenzo Bianconi]

stmmac_rx_vlan() reads the VLAN header straight from skb->data and
removes it with skb_pull(), assuming the header is always in the linear
part of the skb. That is not true once non-linear skbs can reach it: a
program loaded with BPF_F_XDP_HAS_FRAGS can pass up a fragmented frame
whose linear head has been shortened to as little as ETH_HLEN by
bpf_xdp_adjust_head(), and the unguarded skb_pull() then drives skb->len
below skb->data_len, tripping BUG() in __skb_pull().

Pull the VLAN header into the linear part with pskb_may_pull() before
touching it and re-derive the header pointer afterwards, as
pskb_may_pull() may reallocate the skb head. Also move the XDP metadata
written with bpf_xdp_adjust_meta() together with the MAC header when the
tag is popped, so data_meta still points at the metadata after
eth_type_trans() anchors mac_header, instead of at the first bytes of
the destination MAC. Return an error so the callers can drop the frame
when the header cannot be pulled.

Fixes: bba2556efad6 ("net: stmmac: Enable RX via AF_XDP zero-copy")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi at oss.qualcomm.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 45 +++++++++++++++--------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index e929cc0f2312..04dc6dcaa435 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5095,22 +5095,30 @@ static netdev_features_t stmmac_features_check(struct sk_buff *skb,
 	return vlan_features_check(skb, features);
 }
 
-static void stmmac_rx_vlan(struct net_device *dev, struct sk_buff *skb)
+static int stmmac_rx_vlan(struct net_device *dev, struct sk_buff *skb)
 {
-	struct vlan_ethhdr *veth = skb_vlan_eth_hdr(skb);
-	__be16 vlan_proto = veth->h_vlan_proto;
-	u16 vlanid;
+	struct vlan_ethhdr *veth;
 
-	if ((vlan_proto == htons(ETH_P_8021Q) &&
+	if (!pskb_may_pull(skb, VLAN_ETH_HLEN))
+		return -EINVAL;
+
+	veth = skb_vlan_eth_hdr(skb);
+	if ((veth->h_vlan_proto == htons(ETH_P_8021Q) &&
 	     dev->features & NETIF_F_HW_VLAN_CTAG_RX) ||
-	    (vlan_proto == htons(ETH_P_8021AD) &&
+	    (veth->h_vlan_proto == htons(ETH_P_8021AD) &&
 	     dev->features & NETIF_F_HW_VLAN_STAG_RX)) {
+		__be16 vlan_proto = veth->h_vlan_proto;
+		u16 vlanid = ntohs(veth->h_vlan_TCI);
+		u8 meta_len = skb_metadata_len(skb);
+
 		/* pop the vlan tag */
-		vlanid = ntohs(veth->h_vlan_TCI);
-		memmove(skb->data + VLAN_HLEN, veth, ETH_ALEN * 2);
+		memmove(skb->data - meta_len + VLAN_HLEN,
+			skb->data - meta_len, meta_len + ETH_ALEN * 2);
 		skb_pull(skb, VLAN_HLEN);
 		__vlan_hwaccel_put_tag(skb, vlan_proto, vlanid);
 	}
+
+	return 0;
 }
 
 static bool stmmac_rx_need_ic(struct stmmac_priv *priv,
@@ -5530,12 +5538,15 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
 	}
 
 	stmmac_get_rx_hwtstamp(priv, p, np, skb);
-	if (priv->hw->hw_vlan_en)
+	if (priv->hw->hw_vlan_en) {
 		/* MAC level stripping. */
 		stmmac_rx_hw_vlan(priv, priv->hw, p, skb);
-	else
-		/* Driver level stripping. */
-		stmmac_rx_vlan(priv->dev, skb);
+	} else if (stmmac_rx_vlan(priv->dev, skb)) {
+		dev_kfree_skb_any(skb);
+		priv->xstats.rx_dropped++;
+		return;
+	}
+
 	skb->protocol = eth_type_trans(skb, priv->dev);
 
 	if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb))
@@ -6041,12 +6052,14 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 
 		stmmac_get_rx_hwtstamp(priv, p, np, skb);
 
-		if (priv->hw->hw_vlan_en)
+		if (priv->hw->hw_vlan_en) {
 			/* MAC level stripping. */
 			stmmac_rx_hw_vlan(priv, priv->hw, p, skb);
-		else
-			/* Driver level stripping. */
-			stmmac_rx_vlan(priv->dev, skb);
+		} else if (stmmac_rx_vlan(priv->dev, skb)) {
+			dev_kfree_skb_any(skb);
+			rx_dropped++;
+			goto next;
+		}
 
 		skb->protocol = eth_type_trans(skb, priv->dev);
 

-- 
2.56.0