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Re: [PATCH v3] mac80211: Avoid STA expiration timer truncation to u32

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2015-01-23 18:42 GMT+09:00 Johannes Berg <johannes@xxxxxxxxxxxxxxxx>:
> Ok - but that doesn't really disable the timer? Perhaps we should have a
> new userspace API to explicitly disable it? OTOH, worst case I guess
> that means it's like >100 years in the future, so I guess it doesn't
> matter. However, though, you can hardly rely on this fix being present
> in the kernel, so you can't really set such a large value
> unconditionally anyway, no? Otherwise a newer wpa_supplicant running on
> an older kernel would suddenly behave incorrectly. That doesn't seem
> right.
>
> Having an explicit feature to disable plink timeout would perhaps be
> better?

Thank you for your review.

On my environment, HZ macro is 250. So jiffies counts up 250 per seconds.
So jiffies overflows in 199 days.
It is a large value still. But on my arm64 environment, jiffies could over the
u32 max value. Because it looks starts with about 0xffff0000.
So I need this patch. On the i386 environment, it does not occur.

> I'm not convinced this is right. For one, I believe on 32-bit machines
> you'll need to write "0x100000000ULL" instead of the plain constant.
> Perhaps preferably, you'd use use ">= MAX_UINT".

I have written such a code "0x100000000ULL" few years ago. But now,
"0x100000000" works. I re-tested on 64bit.
Anyway I think using "MAX_UINT" is better.

> However, the argument to ieee80211_sta_expire() is an unsigned long (as
> is jiffies), so on 64-bit machines you could even still use the value
> and the conditional isn't needed.

Yes, this is a code for 32bit machine.

> Given these complications, I would prefer having a feature attribute to
> treat e.g. 0 as disabling the timer entirely, and if this feature isn't
> present then have wpa_supplicant instead use a safe value that doesn't
> trigger the kernel bug - e.g. 0xffffffff/1000 [which is the max possible
> HZ].

Looks fine. I will modify this patch.
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