FAILED: patch "[PATCH] net: extend IPv6 exthdr detection of tunneled packets" failed to apply to 6.18-stable tree

[email protected]

author maintainer

2026-10-03 13:17 UTC #0 lore raw

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 5f0764cb1c81a9712bce605d38efe6d844a70b29
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026100321-entering-brewing-b9b5@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5f0764cb1c81a9712bce605d38efe6d844a70b29 Mon Sep 17 00:00:00 2001
From: Willem de Bruijn <[email protected]>
Date: Sat, 26 Sep 2026 10:04:54 -0400
Subject: [PATCH] net: extend IPv6 exthdr detection of tunneled packets

Commit c4336a07eb6b ("net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback") split skb_gso_has_extension_hdr() into mutually exclusive branches on skb->encapsulation. This did not yet address all paths:

1. With skb->encapsulation set, the outer header is not checked. IPv6 tunnels such as ip6_gre and ip6_tunnel add an outer Destination Options header by default (encap_limit). Their GSO packets skip software GSO, then skb_csum_hwoffload_help() sees the outer extension header and calls skb_checksum_help() on the GSO skb, which warns and drops it.

2. Tunnels over IPv6 without an outer transport header, such as ip6_tunnel, leave skb->transport_header at the inner transport header. skb_network_header_len() then spans the outer IPv6, tunnel and inner IP headers, a false positive.

3. UDP tunnels without an inner network header, such as SCTP-in-UDP or PSP, have no inner IPv6 header to check. Decide on the outer header alone.

4. Directly dereferencing inner_ip_hdr(skb)->version without skb_header_pointer() is unsafe.

Instead, check ipv6_ext_hdr(nexthdr) on the outer IPv6 header and, if set, on the inner IPv6 header. Read the headers with skb_header_pointer(). Keep the skb_network_header_len() check when !skb->encapsulation to also catch encapsulated packets without skb->encapsulation (e.g., virtio).

Use the same helper in skb_csum_hwoffload_help(). Its open coded test has the false positive of (2) and ignores the inner header.

Background: checksum offload of tunneled packets invariants:

Non-GSO skb:
- If the inner packet is CHECKSUM_PARTIAL, Local Checksum Offload computes the outer checksum in software and the device offloads only the inner L4 checksum.
- If the inner packet is CHECKSUM_NONE (e.g., SCTP-in-UDP, ESP-in-UDP, Remote Checksum Offload), the device offloads the outer UDP or GRE checksum instead.

GSO skb:
- A device with NETIF_F_GSO_UDP_TUNNEL_CSUM or NETIF_F_GSO_GRE_CSUM computes both inner and outer checksums per segment. The outer checksum is seeded with only the pseudo-header checksum.

A NETIF_F_IPV6_CSUM device must parse through the outer headers to reach the inner ones.

Fixes c4336a07eb6b ("net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback")

Cc [email protected]

Signed-off-by Willem de Bruijn <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

net/core/dev.c +31 ~~-16~~

index 8638c994bbcb..18dc88990510 100644
@@ -3818,20 +3818,36 @@ 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)
+static bool __skb_has_ipv6_ext_hdr(const struct sk_buff *skb, int nhoff)
 {
-	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)));
+	const struct ipv6hdr *ip6h;
+	struct ipv6hdr _ip6h;
+
+	ip6h = skb_header_pointer(skb, nhoff, sizeof(_ip6h), &_ip6h);
+	return ip6h && ip6h->version == 6 && ipv6_ext_hdr(ip6h->nexthdr);
+}
+
+static bool skb_has_ipv6_extension_hdr(const struct sk_buff *skb)
+{
+	if (vlan_get_protocol(skb) == htons(ETH_P_IPV6)) {
+		if (__skb_has_ipv6_ext_hdr(skb, skb_network_offset(skb)))
+			return true;
+
+		/* Catch tunnels without skb->encapsulation (e.g., virtio). */
+		if (!skb->encapsulation &&
+		    skb_transport_header_was_set(skb) &&
+		    skb_network_header_len(skb) != sizeof(struct ipv6hdr))
+			return true;
+	}
+
+	/* Tunnels without an inner network header, such as SCTP-in-UDP or
+	 * PSP, have no inner IP header and thus no inner extension header.
+	 */
+	if (skb->encapsulation && skb_inner_network_header_was_set(skb) &&
+	    __skb_has_ipv6_ext_hdr(skb, skb_inner_network_offset(skb)))
+		return true;
+
+	return false;
 }
 
 static netdev_features_t gso_features_check(const struct sk_buff *skb,

@@ -3886,7 +3902,7 @@ 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_gso_has_extension_hdr(skb))
+	    skb_has_ipv6_extension_hdr(skb))
 		features &= ~(NETIF_F_IPV6_CSUM | NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4);
 
 	return features;

@@ -3988,8 +4004,7 @@ int skb_csum_hwoffload_help(struct sk_buff *skb,
 		return 0;
 
 	if (features & (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM)) {
-		if (vlan_get_protocol(skb) == htons(ETH_P_IPV6) &&
-		    skb_network_header_len(skb) != sizeof(struct ipv6hdr))
+		if (skb_has_ipv6_extension_hdr(skb))
 			goto sw_checksum;
 
 		switch (skb->csum_offset) {

Sasha Levin

maintainer

2026-10-04 00:28 UTC #1 lore raw

PATCH 1/2 net/ipv6: Remove jumbo_remove step from TX path

From: Alice Mikityanska <[email protected]>

[ Upstream commit 1676ebba391dee944988ce3de1c23e038a3121d3 ]

Now that the kernel doesn't insert HBH for BIG TCP IPv6 packets, remove unnecessary steps from the GSO TX path, that used to check and remove HBH.

Signed-off-by Alice Mikityanska <[email protected]>

Acked-by Paolo Abeni <[email protected]>

Reviewed-by Eric Dumazet <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

Remove the BIG TCP jumbo-header exemptions from the GSO feature and checksum offload checks. Keep the existing skb_gso_has_extension_hdr() helper when updating the GSO check so tunneled-packet handling is retained.

The transmit and GRO paths still insert hop-by-hop headers for BIG TCP, so retain their removal during software segmentation. Dropping that cleanup requires the earlier BIG TCP representation changes and is not needed for the subsequent IPv6 extension-header detection fix.

BIG TCP packets with these headers now fall back to software segmentation on devices limited to IPv6 checksum offload, where the retained cleanup removes the synthetic header before producing segments.

[ sashal: Reduced backport -- upstream 1676ebba391de touches 2 file(s), this
backport carries 1. Not backported here:
net/ipv6/ip6_offload.c
This note is generated from the file lists only. ]

Stable-dep-of: 5f0764cb1c81 ("net: extend IPv6 exthdr detection of tunneled packets")

Signed-off-by Sasha Levin <[email protected]>

---
 net/core/dev.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

net/core/dev.c +2 -4

index 6569605cc666a..e42ac7a306d07 100644
@@ -3824,8 +3824,7 @@ 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_gso_has_extension_hdr(skb) &&
-	    !ipv6_has_hopopt_jumbo(skb))
+	    skb_gso_has_extension_hdr(skb))
 		features &= ~(NETIF_F_IPV6_CSUM | NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4);
 
 	return features;

@@ -3928,8 +3927,7 @@ int skb_csum_hwoffload_help(struct sk_buff *skb,
 
 	if (features & (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM)) {
 		if (vlan_get_protocol(skb) == htons(ETH_P_IPV6) &&
-		    skb_network_header_len(skb) != sizeof(struct ipv6hdr) &&
-		    !ipv6_has_hopopt_jumbo(skb))
+		    skb_network_header_len(skb) != sizeof(struct ipv6hdr))
 			goto sw_checksum;
 
 		switch (skb->csum_offset) {

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-10-04 00:28 UTC #2 lore raw

PATCH 2/2 net: extend IPv6 exthdr detection of tunneled packets

From: Willem de Bruijn <[email protected]>

[ Upstream commit 5f0764cb1c81a9712bce605d38efe6d844a70b29 ]