linux-kernel - Re: [PATCH] mac80211: aggregation: Convert timers to use timer

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Message-ID: <CAGXu5jLC4FAXvHxn+N1d_6nSz-MnBAPMeNFKbt4W+fERAxTHZg@mail.gmail.com>
Date:   Wed, 18 Oct 2017 14:02:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     linux-wireless <linux-wireless@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mac80211: aggregation: Convert timers to use timer_setup()

On Wed, Oct 18, 2017 at 1:50 PM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Wed, 2017-10-18 at 07:19 -0700, Kees Cook wrote:
>> On Wed, Oct 18, 2017 at 3:29 AM, Johannes Berg
>> <johannes@...solutions.net> wrote:
>> > > This has been the least trivial timer conversion yet. Given the use of
>> > > RCU and other things I may not even know about, I'd love to get a close
>> > > look at this. I *think* this is correct, as it will re-lookup the tid
>> > > entries when firing the timer.
>> >
>> > I'm not really sure why you're doing the lookup again? That seems
>> > pointless, since you already have the right structure, and already rely
>> > on it being valid. You can't really get a new struct assigned to the
>> > same TID without the old one being destroyed.
>>
>> I couldn't tell what the lifetime expectation was, so I left the
>> re-lookup. I assumed it was possible to have a timer fire after the
>> structure had been removed from the station structure.
>
> Oh, right, I guess that would've been possible in theory. It's not
> actually possible though since the aggregation sessions can't live on
> without a station, so I've already made a follow-up patch to remove the
> indirection.

Okay, cool, thanks.

It seems like I have a similar case in the iwlwifi driver too, but
it's different enough that I'm not sure about that one either. I'll
send that when I've got it ready.

-Kees

-- 
Kees Cook
Pixel Security