linux-kernel - Re: [RFC][PATCH 2/7] kref: Add kref

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Message-ID: <20161117132206.GE3117@twins.programming.kicks-ass.net>
Date:   Thu, 17 Nov 2016 14:22:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
Cc:     David Windsor <dave@...gbits.org>,
        Kees Cook <keescook@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [RFC][PATCH 2/7] kref: Add kref_read()

On Thu, Nov 17, 2016 at 01:01:49PM +0000, Reshetova, Elena wrote:

> >I think the sole motivator is a general distaste of atomic_t, which isn't a good reason at all.
> 
> I don't think anyone has this as motivation. But atomic_t is so
> powerful and flexible that easily ends up being misused (as past CVEs
> shown). 

I don't think using atomic_t as reference count is abuse. There simply
wasn't anything better. The proposed refcount_t cures this.

> Even if we now find all occurrences of atomic_t used as
> refcounter (which we cannot actually guarantee in any case unless
> someone manually reads every line) and convert it to refcount_t, we
> still have atomic_t type present and new usage of it as refount will
> crawl in. It is just a matter of time IMO.

Improve tooling. The patterns shouldn't be _that_ hard to find. Once the
tools are good, new code isn't a problem either.

Anything: atomic*_{{dec,sub}_and_test,{add,sub}_return,fetch_{add,sub}}
followed by a call_rcu()/free().