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Groups > linux.debian.kernel > #91131

Bug#1127597: linux-image-6.12.48+deb13-amd64: GRE6 decap fails

Cross-posted to 2 groups.

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Source: linux
Version: 6.12.48+deb13-amd64
Severity: important
Tags: ipv6
X-Debbugs-Cc: debian-amd64@lists.debian.org
User: debian-amd64@lists.debian.org
Usertags: amd64

Dear Maintainer,

When I boot on the 6.12.48+deb13-amd64 version of the kernel, my GRE6 tunnels stop to work, it seems that decapsulation fail

Rolling back to 6.12.63+deb13-amd64 make them work again, so I _think_ this is not a configuration issue.

I have two GRE6 tunnels on which I run BGP sessions.

Here's a capture of the external interface, filtered on ip6[40] = 47

21:56:44.411270 IP6 (flowlabel 0x7759c, hlim 64, next-header unknown (60) payload length: 92) 2001:41d0:302:2000::2144 > 2a0c:b641:6::: DSTOPT (opt_type 0x04: len=1)(padn) GREv0, Flags [none], length 84
	IP6 (class 0xc0, flowlabel 0x7759c, hlim 255, next-header TCP (6) payload length: 40) 2a0c:b640:fffe::21:2834:2.47098 > 2a0c:b640:fffe::21:2834:1.179: Flags [S], cksum 0xc046 (correct), seq 2822657693, win 65236, options [mss 1388,sackOK,TS val 903776896 ecr 0,nop,wscale 7], length 0
21:56:44.421735 IP6 (flowlabel 0xc3931, hlim 242, next-header unknown (60) payload length: 92) 2a0c:b641:6:: > 2001:41d0:302:2000::2144: DSTOPT (opt_type 0x04: len=1)(padn) GREv0, Flags [none], length 84
	IP6 (class 0xc0, flowlabel 0xc3931, hlim 255, next-header TCP (6) payload length: 40) 2a0c:b640:fffe::21:2834:1.179 > 2a0c:b640:fffe::21:2834:2.47098: Flags [S.], cksum 0x03b1 (correct), seq 1998626730, ack 2822657694, win 64672, options [mss 1388,sackOK,TS val 911965588 ecr 903773822,nop,wscale 7], length 0

We can see the SYN sent by bird, and the SYN/ACK returned by the peer.
Meanwile, when capturing on the gre interfact itself, only the SYNs sent by my side shows up

21:56:43.387145 IP6 (class 0xc0, flowlabel 0xd8556, hlim 255, next-header TCP (6) payload length: 40) 2a0c:b640:fffe::21:2834:2.47098 > 2a0c:b640:fffe::21:2834:1.179: Flags [S], cksum 0x1173 (incorrect -> 0xc446), seq 2822657693, win 65236, options [mss 1388,sackOK,TS val 903775872 ecr 0,nop,wscale 7], length 0
21:56:44.411239 IP6 (class 0xc0, flowlabel 0x7759c, hlim 255, next-header TCP (6) payload length: 40) 2a0c:b640:fffe::21:2834:2.47098 > 2a0c:b640:fffe::21:2834:1.179: Flags [S], cksum 0x1173 (incorrect -> 0xc046), seq 2822657693, win 65236, options [mss 1388,sackOK,TS val 903776896 ecr 0,nop,wscale 7], length 0
21:56:45.435116 IP6 (class 0xc0, flowlabel 0x9203f, hlim 255, next-header TCP (6) payload length: 40) 2a0c:b640:fffe::21:2834:2.47098 > 2a0c:b640:fffe::21:2834:1.179: Flags [S], cksum 0x1173 (incorrect -> 0xbc46), seq 2822657693, win 65236, options [mss 1388,sackOK,TS val 903777920 ecr 0,nop,wscale 7], length 0

ICMP inside the tunnels behave the same (seen from the outer interface, not on the GRE one)

Regards

-- System Information:
Debian Release: 13.3
  APT prefers stable-security
  APT policy: (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.12.63+deb13-amd64 (SMP w/1 CPU thread; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages linux-image-6.12.69+deb13-amd64 depends on:
ii  initramfs-tools [linux-initramfs-tool]  0.148.3
ii  kmod                                    34.2-2
ii  linux-base                              4.12

-- Package-specific info:
** Model information
sys_vendor: OpenStack Foundation
product_name: OpenStack Nova
product_version: 19.3.2
chassis_vendor: QEMU
chassis_version: pc-i440fx-9.2
bios_vendor: SeaBIOS
bios_version: 1.16.3-debian-1.16.3-2~bpo12+1

** Configuration for modprobe:
blacklist pcspkr
blacklist arkfb
blacklist aty128fb
blacklist atyfb
blacklist radeonfb
blacklist cirrusfb
blacklist cyber2000fb
blacklist kyrofb
blacklist matroxfb_base
blacklist mb862xxfb
blacklist neofb
blacklist pm2fb
blacklist pm3fb
blacklist s3fb
blacklist savagefb
blacklist sisfb
blacklist tdfxfb
blacklist tridentfb
blacklist vt8623fb
options snd_pcsp index=-2
options cx88_alsa index=-2
options snd_atiixp_modem index=-2
options snd_intel8x0m index=-2
options snd_via82xx_modem index=-2
options bonding max_bonds=0
options dummy numdummies=0
options ifb numifbs=0

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Thread

Bug#1127597: linux-image-6.12.48+deb13-amd64: GRE6 decap fails Bastien Durel <bastien.durel@geekwu.org> - 2026-02-10 10:20 +0100
  Bug#1127597: additional info Bastien Durel <bastien@durel.org> - 2026-02-10 11:10 +0100
  Bug#1127597: linux-image-6.12.48+deb13-amd64: GRE6 decap fails Tobias Fiebig <tobias@fiebig.nl> - 2026-02-10 13:30 +0100
  Processed: Re: Bug#1127597: linux-image-6.12.48+deb13-amd64: GRE6  decap fails "Debian Bug Tracking System" <owner@bugs.debian.org> - 2026-02-10 13:30 +0100
  Bug#1127597: Info received (Bug#1127597: linux-image-6.12.48+deb13-amd64: GRE6 decap fails) Tobias Fiebig <tobias@fiebig.nl> - 2026-02-10 13:50 +0100
  Bug#1127597: linux-image-6.19.0+debian+tj: v6.12.69 - ip6gre regression Tj <tj.iam.tj@proton.me> - 2026-02-10 23:00 +0100
  Bug#1127597: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails Tj <tj.iam.tj@proton.me> - 2026-02-11 06:10 +0100
    Bug#1127597: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails Greg KH <gregkh@linuxfoundation.org> - 2026-02-11 06:40 +0100
  Bug#1127597: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails F!nTcH <fintch@fintch.org> - 2026-03-04 18:50 +0100
    Bug#1127597: Regression: v6.12.67 ip6_tunnel: ip6gre decapsulation fails Salvatore Bonaccorso <carnil@debian.org> - 2026-03-05 10:30 +0100

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