On 12.09.23 12:27, Florian Westphal wrote:

Linux regression tracking (Thorsten Leemhuis) [off-list ref] wrote:

quoted

On 12.09.23 00:57, Pablo Neira Ayuso wrote:

quoted

Userspace nftables v1.0.6 generates incorrect bytecode that hits a new
kernel check that rejects adding rules to bound chains. The incorrect
bytecode adds the chain binding, attach it to the rule and it adds the
rules to the chain binding. I have cherry-picked these three patches
for nftables v1.0.6 userspace and your ruleset restores fine.
[...]

Hmmmm. Well, this sounds like a kernel regression to me that normally
should be dealt with on the kernel level, as users after updating the
kernel should never have to update any userspace stuff to continue what
they have been doing before the kernel update.

This is a combo of a userspace bug and this new sanity check that
rejects the incorrect ordering (adding rules to the already-bound
anonymous chain).

nf_tables uses a transaction allor-nothing model, this means that any
error that occurs during a transaction has to be reverse/undo all the
pending changes.  This has caused a myriad of bugs already.

So while this can be theoretically fixed in the kernel I don't see
a sane way to do it.  Error unwinding / recovery from deeply nested
errors is already too complex for my taste.

quoted

Can't the kernel somehow detect the incorrect bytecode and do the right
thing(tm) somehow?

Theoretically yes, but I don't feel competent enough to do it, just look
at all the UaF bugs of the past month.

Thx for the answer. FWIW, as this was a judgement call I mentioned this
in my last regression report to Linus; he didn't reply, so I guess it is
-- and will remove this issue from my tracking:

#regzbot resolve: can be solved by a nftables userspace update; not
nice, but likely best solution in this case
#regzbot ignore-activity

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
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