linux-kernel - Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount

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Date:   Mon, 10 Jul 2017 06:19:32 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     "Reshetova\, Elena" <elena.reshetova@...el.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz\@infradead.org" <peterz@...radead.org>,
        "gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
        "akpm\@linux-foundation.org" <akpm@...ux-foundation.org>,
        "mingo\@redhat.com" <mingo@...hat.com>,
        "serge\@hallyn.com" <serge@...lyn.com>,
        "arozansk\@redhat.com" <arozansk@...hat.com>,
        "dave\@stgolabs.net" <dave@...olabs.net>,
        "keescook\@chromium.org" <keescook@...omium.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t

Alexey Dobriyan <adobriyan@...il.com> writes:

> On Mon, Jul 10, 2017 at 11:37 AM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
>> "Reshetova, Elena" <elena.reshetova@...el.com> writes:
>>
>> 2>> Elena Reshetova <elena.reshetova@...el.com> writes:
>>>>
>>>> > refcount_t type and corresponding API should be
>>>> > used instead of atomic_t when the variable is used as
>>>> > a reference counter. This allows to avoid accidental
>>>> > refcounter overflows that might lead to use-after-free
>>>> > situations.
>>>>
>>>> In this patch you can see all of the uses of the count.
>>>> What accidental refcount overflows are possible?
>>>
>>> Even if one can guarantee and prove that in the current implementation
>>> there are no overflows possible, we can't say that for
>>> sure for any future implementation. Bugs might always happen
>>> unfortunately, but if we convert the refcounter to a safer
>>> type we can be sure that overflows are not possible.
>>>
>>> Does it make sense to you?
>>
>> Not for code that is likely to remain unchanged for a decade no.
>>
>> This looks like a large set of unautomated changes without any real
>> thought put into it.  That almost always results in a typo somewhere
>> that breaks things.
>
> This is nonsense. The wrong code would simply emit a warning
> which are caught very quickly.

That depends on the typo.

Eric