Hello Salvatore, I would actually give reverting that one a shot first. Let me see if I can quickly build a kernel without that specific patch.
With best regards, Tobias On Tue, 2026-02-10 at 13:18 +0100, Salvatore Bonaccorso wrote: > Control: tags -1 + moreinfo > > Hi BAstien, hi Tobias, > > On Tue, Feb 10, 2026 at 09:57:15AM +0100, Bastien Durel wrote: > > Source: linux > > Version: 6.12.48+deb13-amd64 > > Severity: important > > Tags: ipv6 > > X-Debbugs-Cc: [email protected] > > User: [email protected] > > 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) > > Thanks for your both reports. So this look we introduced a regression > from the preivous 6.12.63-1 to 6.12.69-1 with gre6. > > I will have a look at this shortly. > > If any of you both has a testing environment where you can bisect the > upstream changes between 6.12.63 and 6.12.69 to clearly isolate the > breaking change that would be great, let me know if you need > instructions on how to do it. It might be the ip6_gre change > db5b4e39c4e6 ("ip6_gre: make ip6gre_header() robust") in 6.12.64. > > Regards, > Salvatore -- Dr.-Ing. Tobias Fiebig T +31 616 80 98 99 M [email protected]
