[Cake] NLA_F_NESTED is missing

[Toke Høiland-Jørgensen]

Dean Scarff <dos at scarff.id.au> writes:

>  On Mon, 02 Nov 2020 13:37:00 +0100, Toke wrote:
>> Dean Scarff <dos at scarff.id.au> writes:
>>
>>>  Hi,
>>>
>>>  I've been happily running the out-of-tree sch_cake on my Raspberry 
>>> Pi
>>>  since 2015.  However, I recently upgraded my kernel (to 5.4.72 from
>>>  Raspbian's raspberrypi-kernel 1.20201022-1), which comes with the
>>>  sch_cake in mainline.  Now, when running:
>>>
>>>    sudo /sbin/tc qdisc add dev ppp0 root cake
>>>
>>>  I get the error:
>>>
>>>    Error: NLA_F_NESTED is missing.
>>>
>>>  I get this error with the sch_cake in mainline, and also with 
>>> sch_cake
>>>  built out-of-tree.  I also get the error with both Debian's 
>>> iproute2
>>>  5.9.0-1 (built myself via debian/rules) and "tc" from dtaht's 
>>> tc-adv
>>>  repo.
>>>
>>>  Any ideas on what this error means and how to fix it?
>>
>> I just tried building a 5.4.72 kernel and couldn't reproduce this, so 
>> it
>> seems it's a fault with the raspberry pi kernel; I guess opening a 
>> bug
>> against that would be the way to go?
>>
>> As for what's actually causing this, I couldn't find anything obvious
>> that touches this code in the qdisc layer; but I suppose it has
>> something to do with the core qdisc netlink parsing code?
>>
>> -Toke
>
>  Thanks for the data point.
>
>  For the record, the relevant kernel source is:
>  https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/net/netlink.h?h=v5.4.72#n1143
>  and the Pi branch:
>  https://github.com/raspberrypi/linux/blob/raspberrypi-kernel_1.20201022-1/include/net/netlink.h#L1143
>
>  It seems very unlikely that the Pi folks are patching the netlink 
>  stuff, so I don't think I'll get much traction there unless I can call 
>  out something specifically wrong with their patchset.

Well, something odd is certainly going on. The error message you're
quoting comes form a part of the netlink parsing code (in the kernel)
that shouldn't even be hit by the qdisc addition: NLA_F_NESTED parsing
is only enabled in 'strict' validation mode, which is not used for
qdiscs.

So IDK, maybe a compiler issue or a bit that gets set wrong somewhere?
Bisecting the kernel may be the only option here, I don't think you're
going to find anything in userspace...

-Toke