XPost: linux.debian.kernel   
   From: carnil@debian.org   
      
   Hi,   
      
   On Fri, Feb 13, 2026 at 05:12:07PM +0200, Hostinger NOC wrote:   
   > Package: linux-image-6.1.0-43-amd64   
   > Version: 6.1.162-1   
   > Severity: important   
   > Tags: upstream   
   >   
   >   Hello,   
   >   
   >   The ip6_tunnel kernel module is broken in linux-image-6.1.0-43-amd64   
   >   (upstream 6.1.162). IPv6 tunnels (mode "any") fail to encapsulate or   
   >   transmit any packets.   
   >   
   >   WORKING CONFIGURATION:   
   >   - Kernel: 6.1.0-37-amd64 (upstream 6.1.140)   
   >   - Tunnel works correctly with identical configuration   
   >   
   >   BROKEN CONFIGURATION:   
   >   - Kernel: 6.1.0-43-amd64 (upstream 6.1.162)   
   >   - Same tunnel configuration fails completely   
   >   
   >   REPRODUCTION STEPS:   
   >   1. Create IPv6 tunnel with mode "any":   
   >      ip link add tun0 type ip6tnl mode any \   
   >        remote 2001:db8::2 \   
   >        local 2001:db8::1 \   
   >        encaplimit 4   
   >      ip addr add 192.0.2.1/30 dev tun0   
   >      ip addr add 2001:db8:1::1/126 dev tun0   
   >      ip link set tun0 up mtu 1500   
   >   
   >   2. Send traffic through tunnel:   
   >      ping -c 3 -I tun0 192.0.2.2   
   >   
   >   3. Monitor physical interface:   
   >      tcpdump -i eth0 -nn 'ip6 and host 2001:db8::2'   
   >   
   >   EXPECTED BEHAVIOR (kernel 6.1.0-37):   
   >   - tcpdump shows encapsulated packets with protocol 60 (DSTOPT) or 4 (IPIP)   
   >   - Tunnel traffic flows successfully   
   >   
   >   ACTUAL BEHAVIOR (kernel 6.1.0-43):   
   >   - tcpdump captures ZERO packets   
   >   - TX counter increments on tunnel interface but packets disappear in   
   > kernel   
   >   - RX packets show errors   
   >   
   >   EVIDENCE - Side-by-side comparison:   
   >   
   >   Kernel 6.1.0-37 (WORKING):   
   >     Protocol 60 (DSTOPT) packets visible on wire   
   >     Encapsulation functioning correctly   
   >   
   >   Kernel 6.1.0-43 (BROKEN):   
   >     0 packets captured   
   >     No packets transmitted to physical interface   
   >   
   >   SYSTEM INFORMATION:   
   >   - Debian version: 12 (bookworm)   
   >   - Architecture: amd64   
   >   - Broken kernel: 6.1.0-43-amd64 (6.1.162-1)   
   >   - Working kernel: 6.1.0-37-amd64 (6.1.140-1)   
   >   - Boot parameters tested: default and mitigations=off (both fail)   
   >   
   >   IMPACT:   
   >   - All IPv6 tunnels using ip6tnl module are affected   
   >   - Workaround: downgrade to 6.1.0-37   
   >   
   >   ADDITIONAL NOTES:   
   >   - Issue persists regardless of tunnel parameters (MTU, encaplimit,   
   > offloads)   
   >   - Module parameter changes have no effect   
   >   - Issue affects both encapsulation (TX) and decapsulation (RX)   
   >   - No relevant errors in dmesg or kernel logs   
   >   
   >   Could you please investigate this regression? Is there any additional   
   >   debugging information or testing I can provide to help identify the root   
   > cause?   
   >   Would additional debugging output be helpful? I can provide kernel   
   >   logs, strace output, or test patches if needed.   
      
   See #1127597.   
      
   Can you confirm that applying 9990ddf47d41 ("net: tunnel: make   
   skb_vlan_inet_prepare() return drop reasons") on top as well of   
   6.1.162-1 (or 6.1.163 upstream) fixes the issue and report back   
   please?   
      
   Regards,   
   Salvatore   
      
   --- SoupGate-Win32 v1.05   
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