netdev - [PATCH net] r8169: Fix possible ring buffer corruption on fragmented Tx packets

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Date: Tue, 21 May 2024 22:20:36 +0100
From: Ken Milmore <ken.milmore@...il.com>
To: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
 Realtek linux nic maintainers <nic_swsd@...ltek.com>
Subject: [PATCH net] r8169: Fix possible ring buffer corruption on fragmented
 Tx packets

An issue was found on the RTL8125b when transmitting small fragmented
packets, whereby invalid entries were inserted into the transmit ring
buffer, subsequently leading to calls to dma_unmap_single() with a null
address.

This was caused by rtl8169_start_xmit() not noticing changes to nr_frags
which may occur when small packets are padded (to work around hardware
quirks) in rtl8169_tso_csum_v2().

To fix this, postpone inspecting nr_frags until after any padding has been
applied.

Fixes: 9020845fb5d6 ("r8169: improve rtl8169_start_xmit")
Signed-off-by: Ken Milmore <ken.milmore@...il.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 86a6d4225bc..86ed9189d5f 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -4337,12 +4337,12 @@ static void rtl8169_doorbell(struct rtl8169_private *tp)
 static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 				      struct net_device *dev)
 {
-	unsigned int frags = skb_shinfo(skb)->nr_frags;
 	struct rtl8169_private *tp = netdev_priv(dev);
 	unsigned int entry = tp->cur_tx % NUM_TX_DESC;
 	struct TxDesc *txd_first, *txd_last;
 	bool stop_queue, door_bell;
 	u32 opts[2];
+	unsigned int frags;
 
 	if (unlikely(!rtl_tx_slots_avail(tp))) {
 		if (net_ratelimit())
@@ -4364,6 +4364,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	txd_first = tp->TxDescArray + entry;
 
+	frags = skb_shinfo(skb)->nr_frags;
 	if (frags) {
 		if (rtl8169_xmit_frags(tp, skb, opts, entry))
 			goto err_dma_1;
-- 
2.39.2