Bug#1106321: iproute2: "ip monitor" fails with current trixie's linux kernel / iproute2 combination

[David Ahern <dsahern@kernel.org>]

On 5/22/25 4:55 PM, Luca Boccassi wrote:
> On Thu, 22 May 2025 at 20:41, Adel Belhouane <bugs.a.b@free.fr> wrote:
>>
>> Package: iproute2
>> Version: 6.14.0-3
>> Severity: normal
>> X-Debbugs-Cc: bugs.a.b@free.fr
>>
>> Dear Maintainer,
>>
>> Having iproute2 >= 6.14 while running a linux kernel < 6.14
>> triggers this bug (tested using debian-13-nocloud-amd64-daily-20250520-2118.qcow2)
>>
>>     root@localhost:~# ip monitor
>>     Failed to add ipv4 mcaddr group to list
>>
>> More specifically this subcommand, which didn't exist in iproute2 6.13
>> is affected:
>>
>>     root@localhost:~# ip mon maddr
>>     Failed to add ipv4 mcaddr group to list
>>     root@localhost:~# ip -6 mon maddr
>>     Failed to add ipv6 mcaddr group to list
>>
>> causing the generic "ip monitor" command to fail.
>>
>> As trixie will use a 6.12.x kernel, trixie is affected.
>>
>> bookworm's iproute2/bookworm-backports is also affected since currently
>> bookworm's backport kernel is also 6.12.x
>>
>> Workarounds:
>> * upgrade the kernel to experimental's (currently) 6.14.6-1~exp1
>> * downgrade iproute2 to 6.13.0-1 (using snapshot.d.o)
>> * on bookworm downgrade (using snapshot.d.o)
>>   iproute2 backport to 6.13.0-1~bpo12+1
>>
>> Details I could gather:
>>
>> This appears to come from this iproute2 6.14's commit:
>>
>> https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?h=v6.14.0&id=7240e0e40f8332dd9f11348700c0c96b8df4ca5b
>>
>> which appears to depend on new kernel 6.14 rtnetlink features as described
>> in Kernelnewbies ( https://kernelnewbies.org/Linux_6.14#Networking ):
>>
>> Add ipv6 anycast join/leave notifications
>>
>> with this (kernel 6.14) commit:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=33d97a07b3ae6fa713919de4e1864ca04fff8f80
> 
> Hi Stephen and David,
> 
> It looks like there's a regression in iproute2 6.14, and 'ip monitor'
> no longer works with kernels < 6.14. Could you please have a look when
> you have a moment? Thanks!

were not a lot of changes, so most likely the multiaddress or anycast
address changes from Yuyang Huang. Please take a look.