Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

[Tj]

ip6gre tunnels fail to be decapsulated in v6.12.67 so never appears on 
the GRE interface.

Reverting the following commit fixes it:

commit df5ffde9669314500809bc498ae73d6d3d9519ac
Author: Eric Dumazet <edumazet@google.com>
Date:   Wed Jan 7 16:31:09 2026 +0000

     ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()

     [ Upstream commit 81c734dae203757fb3c9eee6f9896386940776bd ]

v6.19 works but I've not been able to identify a subsequent commit that 
should also be backported to the stable tree.

Re: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

[Tj]

Apologies for not including more information for upstream in my original 
report.

I replied to the Debian bug that has all the information and logs and 
forgot there was no link included:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1127597

Re: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

[Greg KH]

On Wed, Feb 11, 2026 at 05:04:04AM +0000, Tj wrote:
> ip6gre tunnels fail to be decapsulated in v6.12.67 so never appears on 
> the GRE interface.
> 
> Reverting the following commit fixes it:
> 
> commit df5ffde9669314500809bc498ae73d6d3d9519ac
> Author: Eric Dumazet <edumazet@google.com>
> Date:   Wed Jan 7 16:31:09 2026 +0000
> 
>      ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()
> 
>      [ Upstream commit 81c734dae203757fb3c9eee6f9896386940776bd ]
> 
> v6.19 works but I've not been able to identify a subsequent commit that 
> should also be backported to the stable tree.

Please see this thread:
	https://lore.kernel.org/r/CANn89iL5ksZZCJr7SK9=4Sw6EejdOzr5_m6pBMM8RVtbLy_ACA@mail.gmail.com

I think that should fix this, right?

thanks,

greg k-h

Re: Bug#1127597: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

[Salvatore Bonaccorso]

[-- Attachment #1: Type: text/plain, Size: 1407 bytes --]

Hi Bastien, Tobias, Manuel,

On Wed, Feb 11, 2026 at 06:29:56AM +0100, Greg KH wrote:
> On Wed, Feb 11, 2026 at 05:04:04AM +0000, Tj wrote:
> > ip6gre tunnels fail to be decapsulated in v6.12.67 so never appears on 
> > the GRE interface.
> > 
> > Reverting the following commit fixes it:
> > 
> > commit df5ffde9669314500809bc498ae73d6d3d9519ac
> > Author: Eric Dumazet <edumazet@google.com>
> > Date:   Wed Jan 7 16:31:09 2026 +0000
> > 
> >      ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()
> > 
> >      [ Upstream commit 81c734dae203757fb3c9eee6f9896386940776bd ]
> > 
> > v6.19 works but I've not been able to identify a subsequent commit that 
> > should also be backported to the stable tree.
> 
> Please see this thread:
> 	https://lore.kernel.org/r/CANn89iL5ksZZCJr7SK9=4Sw6EejdOzr5_m6pBMM8RVtbLy_ACA@mail.gmail.com
> 
> I think that should fix this, right?

Can you test building v6.12.69 (or the Debian kernel, see instructions
below) with the attached patch which would be the above mentioned fix,
and report back here?

Manuel, you mentioned you see the problem as well on 6.1.162 (where
ineed the patches were backported as well), can you double-check as
well that the patch fixes your seen regression?

To build the Debian kernel with a single-patch on top applied follow
https://kernel-team.pages.debian.net/kernel-handbook/ch-common-tasks.html#id-1.6.6.4

Regards,
Salvatore

[-- Attachment #2: 0001-net-tunnel-make-skb_vlan_inet_prepare-return-drop-re.patch --]
[-- Type: text/x-diff, Size: 3894 bytes --]

From 9990ddf47d4168088e2246c3d418bf526e40830d Mon Sep 17 00:00:00 2001
From: Menglong Dong <menglong8.dong@gmail.com>
Date: Wed, 9 Oct 2024 10:28:21 +0800
Subject: [PATCH] net: tunnel: make skb_vlan_inet_prepare() return drop reasons

Make skb_vlan_inet_prepare return the skb drop reasons, which is just
what pskb_may_pull_reason() returns. Meanwhile, adjust all the call of
it.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 drivers/net/bareudp.c          |  4 ++--
 drivers/net/geneve.c           |  4 ++--
 drivers/net/vxlan/vxlan_core.c |  2 +-
 include/net/ip_tunnels.h       | 13 ++++++++-----
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c
index e057526448d7..fa2dd76ba3d9 100644
--- a/drivers/net/bareudp.c
+++ b/drivers/net/bareudp.c
@@ -317,7 +317,7 @@ static int bareudp_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be32 saddr;
 	int err;
 
-	if (!skb_vlan_inet_prepare(skb, skb->protocol != htons(ETH_P_TEB)))
+	if (skb_vlan_inet_prepare(skb, skb->protocol != htons(ETH_P_TEB)))
 		return -EINVAL;
 
 	if (!sock)
@@ -387,7 +387,7 @@ static int bareudp6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
-	if (!skb_vlan_inet_prepare(skb, skb->protocol != htons(ETH_P_TEB)))
+	if (skb_vlan_inet_prepare(skb, skb->protocol != htons(ETH_P_TEB)))
 		return -EINVAL;
 
 	if (!sock)
diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 7f611c74eb62..2f29b1386b1c 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -827,7 +827,7 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
-	if (!skb_vlan_inet_prepare(skb, inner_proto_inherit))
+	if (skb_vlan_inet_prepare(skb, inner_proto_inherit))
 		return -EINVAL;
 
 	if (!gs4)
@@ -937,7 +937,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	__be16 sport;
 	int err;
 
-	if (!skb_vlan_inet_prepare(skb, inner_proto_inherit))
+	if (skb_vlan_inet_prepare(skb, inner_proto_inherit))
 		return -EINVAL;
 
 	if (!gs6)
diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 6e9a3795846a..916c3880832e 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2356,7 +2356,7 @@ void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 	__be32 vni = 0;
 
 	no_eth_encap = flags & VXLAN_F_GPE && skb->protocol != htons(ETH_P_TEB);
-	if (!skb_vlan_inet_prepare(skb, no_eth_encap))
+	if (skb_vlan_inet_prepare(skb, no_eth_encap))
 		goto drop;
 
 	old_iph = ip_hdr(skb);
diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index 7fc2f7bf837a..4e4f9e24c9c1 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -467,11 +467,12 @@ static inline bool pskb_inet_may_pull(struct sk_buff *skb)
 
 /* Variant of pskb_inet_may_pull().
  */
-static inline bool skb_vlan_inet_prepare(struct sk_buff *skb,
-					 bool inner_proto_inherit)
+static inline enum skb_drop_reason
+skb_vlan_inet_prepare(struct sk_buff *skb, bool inner_proto_inherit)
 {
 	int nhlen = 0, maclen = inner_proto_inherit ? 0 : ETH_HLEN;
 	__be16 type = skb->protocol;
+	enum skb_drop_reason reason;
 
 	/* Essentially this is skb_protocol(skb, true)
 	 * And we get MAC len.
@@ -492,11 +493,13 @@ static inline bool skb_vlan_inet_prepare(struct sk_buff *skb,
 	/* For ETH_P_IPV6/ETH_P_IP we make sure to pull
 	 * a base network header in skb->head.
 	 */
-	if (!pskb_may_pull(skb, maclen + nhlen))
-		return false;
+	reason = pskb_may_pull_reason(skb, maclen + nhlen);
+	if (reason)
+		return reason;
 
 	skb_set_network_header(skb, maclen);
-	return true;
+
+	return SKB_NOT_DROPPED_YET;
 }
 
 static inline int ip_encap_hlen(struct ip_tunnel_encap *e)
-- 
2.51.0

Re: Bug#1127597: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

[Bastien Durel]

Le mercredi 11 février 2026 à 08:39 +0100, Salvatore Bonaccorso a
écrit :
> Hi Bastien, Tobias, Manuel,
> 
> On Wed, Feb 11, 2026 at 06:29:56AM +0100, Greg KH wrote:
> > On Wed, Feb 11, 2026 at 05:04:04AM +0000, Tj wrote:
> > > ip6gre tunnels fail to be decapsulated in v6.12.67 so never
> > > appears on 
> > > the GRE interface.
> > > 
> > > Reverting the following commit fixes it:
> > > 
> > > commit df5ffde9669314500809bc498ae73d6d3d9519ac
> > > Author: Eric Dumazet <edumazet@google.com>
> > > Date:   Wed Jan 7 16:31:09 2026 +0000
> > > 
> > >      ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()
> > > 
> > >      [ Upstream commit 81c734dae203757fb3c9eee6f9896386940776bd ]
> > > 
> > > v6.19 works but I've not been able to identify a subsequent
> > > commit that 
> > > should also be backported to the stable tree.
> > 
> > Please see this thread:
> > 	
> > https://lore.kernel.org/r/CANn89iL5ksZZCJr7SK9=4Sw6EejdOzr5_m6pBMM
> > 8RVtbLy_ACA@mail.gmail.com
> > 
> > I think that should fix this, right?
> 
> Can you test building v6.12.69 (or the Debian kernel, see
> instructions
> below) with the attached patch which would be the above mentioned
> fix,
> and report back here?
> 
> Manuel, you mentioned you see the problem as well on 6.1.162 (where
> ineed the patches were backported as well), can you double-check as
> well that the patch fixes your seen regression?
> 
> To build the Debian kernel with a single-patch on top applied follow
> https://kernel-team.pages.debian.net/kernel-handbook/ch-common-tasks.html#id-1.6.6.4


Hello.

I built a new kernel following these instructions, and it fixes the
problem:

root@gre-test:~# uname -a
Linux gre-test 6.12+unreleased-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.69-1a~test (2026-02-11) x86_64 GNU/Linux
root@gre-test:~# ping fd3c:aa96:f408:700::1
PING fd3c:aa96:f408:700::1 (fd3c:aa96:f408:700::1) 56 data bytes
64 bytes from fd3c:aa96:f408:700::1: icmp_seq=1 ttl=64 time=2.55 ms
64 bytes from fd3c:aa96:f408:700::1: icmp_seq=2 ttl=64 time=2.42 ms
64 bytes from fd3c:aa96:f408:700::1: icmp_seq=3 ttl=64 time=2.36 ms
^C
--- fd3c:aa96:f408:700::1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 2.362/2.444/2.551/0.079 ms

Best regards,

-- 
Bastien

Re: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails

[Tj]

On 11/02/2026 05:29, Greg KH wrote:
> Please see this thread:
> 	https://lore.kernel.org/r/CANn89iL5ksZZCJr7SK9=4Sw6EejdOzr5_m6pBMM8RVtbLy_ACA@mail.gmail.com
>
> I think that should fix this, right?

Confirmed. Adding this patch on .67, and .70, resolves the issue.

Thank-you.