Re: [PATCH net v3] ipv6: reject wrapped temporary address preferred lifetimes

[Xia Yan]

On 11/1/26 22:08, Alex Henrie wrote:
> Is there another combination of parameters that might cause a problem?

Hi Alex,

Thanks for explaining the reasoning behind the clamp. I was wrong
about creation eventually being refused as the public address gets
older. I had missed the "+ age" in cfg.valid_lft.

With an infinite-lifetime parent, cfg.valid_lft grows with age too.
For the values you tested, I don't see an age-dependent cutoff in
that lifetime check. Normal successful regenerations don't reach the
retry limit either: addrconf_verify_rtnl() resets the parent's
regen_count before each regeneration. Repeated ipv6_add_addr() or DAD
failures can still exhaust the retries.

I don't have a reproducer for another refusal case.

The remaining worry for me is retention. With a short preferred
lifetime and temp_valid_lft at its two-day default, deprecated
temporary addresses stay on the interface until their valid lifetime
expires, and this path does not check max_addresses. Your 90-second
configuration ages them out fast; with the default I would expect
many more addresses held at once, but I have not tested that or
measured the cost. The creation rate also depends on DAD timing, so
my earlier one-address-per-second estimate was too definite.

Thanks,
Xia