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net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback

PATCH Applied Willem de Bruijn 2 participants 2 messages Mar 20 – Mar 24

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Willem de Bruijn

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PATCH 1/1 net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback

From: Willem de Bruijn <[email protected]>

NETIF_F_IPV6_CSUM only advertises support for checksum offload of packets without IPv6 extension headers. Packets with extension headers must fall back onto software checksumming. Since TSO depends on checksum offload, those must revert to GSO.

The below commit introduces that fallback. It always checks network header length. For tunneled packets, the inner header length must be checked instead. Extend the check accordingly.

A special case is tunneled packets without inner IP protocol. Such as RFC 6951 SCTP in UDP. Those are not standard IPv6 followed by transport header either, so also must revert to the software GSO path.

Cc [email protected]
Fixes 864e3396976e ("net: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM")
Reported-by Tangxin Xie <[email protected]>
Closes https://lore.kernel.org/netdev/[email protected]/ open here
Suggested-by Paolo Abeni <[email protected]>
Signed-off-by Willem de Bruijn <[email protected]>
---
 net/core/dev.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)
net/core/dev.c +17 -5
index 14a83f2035b9..fc5557062414 100644
@@ -3769,6 +3769,22 @@ static netdev_features_t dflt_features_check(struct sk_buff *skb,
 	return vlan_features_check(skb, features);
 }
 
+static bool skb_gso_has_extension_hdr(const struct sk_buff *skb)
+{
+	if (!skb->encapsulation)
+		return ((skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6 ||
+			 (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
+			  vlan_get_protocol(skb) == htons(ETH_P_IPV6))) &&
+			skb_transport_header_was_set(skb) &&
+			skb_network_header_len(skb) != sizeof(struct ipv6hdr));
+	else
+		return (!skb_inner_network_header_was_set(skb) ||
+			((skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6 ||
+			  (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
+			   inner_ip_hdr(skb)->version == 6)) &&
+			 skb_inner_network_header_len(skb) != sizeof(struct ipv6hdr)));
+}
+
 static netdev_features_t gso_features_check(const struct sk_buff *skb,
 					    struct net_device *dev,
 					    netdev_features_t features)

@@ -3816,11 +3832,7 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb,
 	 * so neither does TSO that depends on it.
 	 */
 	if (features & NETIF_F_IPV6_CSUM &&
-	    (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6 ||
-	     (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
-	      vlan_get_protocol(skb) == htons(ETH_P_IPV6))) &&
-	    skb_transport_header_was_set(skb) &&
-	    skb_network_header_len(skb) != sizeof(struct ipv6hdr))
+	    skb_gso_has_extension_hdr(skb))
 		features &= ~(NETIF_F_IPV6_CSUM | NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4);
 
 	return features;
Signature · 1 line
2.53.0.959.g497ff81fa9-goog
CI Applied
#1 lore raw
This patch was applied to netdev/net.git (main) by Paolo Abeni <[email protected]>:

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <[email protected]>:

Quoted 8 lines · On Fri, 20 Mar 2026 15:01:46 -0400 you wrote:

From: Willem de Bruijn <[email protected]>

NETIF_F_IPV6_CSUM only advertises support for checksum offload of packets without IPv6 extension headers. Packets with extension headers must fall back onto software checksumming. Since TSO depends on checksum offload, those must revert to GSO.

[...]

Here is the summary with links:
- [net] net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback

    https://git.kernel.org/netdev/net/c/c4336a07eb6b

You are awesome, thank you!

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