From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	"Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 0942/1250] net: stmmac: add TSO check for header length
Date: Thu, 17 Sep 2026 16:12:17 +0100
Message-ID: <20260917151617.555014672@linuxfoundation.org>
In-Reply-To: <20260917151551.901433442@linuxfoundation.org>
References: <20260917151551.901433442@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

[ Upstream commit 6732e474f880468435a79d05811c8c814c5d71f8 ]

According to the STM32MP151 documentation which covers dwmac v4.2, the
hardware TSO feature can handle header lengths up to a maximum of 1023
bytes.

Add a .ndo_features_check() method implementation to check the header
length meets these requirements, otherwise fall back to software GSO.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1w7ptO-0000000EatC-39il@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 5e38d732ec67 ("net: stmmac: fix TX descriptor availability check for TSO traffic")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c   | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 609f056d4a70f..49651dc792278 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4176,6 +4176,20 @@ static size_t stmmac_tso_header_size(struct sk_buff *skb)
 	return size;
 }
 
+/* STM32MP151 (dwmac v4.2) and STM32MP25xx (dwmac v5.3) states for TDES2 normal
+ * (read format) descriptor that the maximum header length supported for the
+ * TSO feature is 1023 bytes.
+ *
+ * While IPv4 is limited to MAC+VLAN+IPv4+ext+TCP+ext = 138 bytes, the IPv6
+ * extension headers aren't similarly limited.
+ */
+static bool stmmac_tso_valid_packet(struct sk_buff *skb)
+{
+	size_t header_len = stmmac_tso_header_size(skb);
+
+	return header_len <= 1023;
+}
+
 /**
  *  stmmac_tso_xmit - Tx entry point of the driver for oversized frames (TSO)
  *  @skb : the socket buffer
@@ -4754,7 +4768,8 @@ static netdev_features_t stmmac_features_check(struct sk_buff *skb,
 
 	if (skb_is_gso(skb)) {
 		queue = skb_get_queue_mapping(skb);
-		if (!stmmac_tso_channel_permitted(netdev_priv(dev), queue))
+		if (!stmmac_tso_channel_permitted(netdev_priv(dev), queue) ||
+		    !stmmac_tso_valid_packet(skb))
 			features &= ~NETIF_F_GSO_MASK;
 	}
 
-- 
2.53.0