From: ebiederm@xmission.com (Eric W. Biederman)
To: "Reshetova\, Elena" <elena.reshetova@intel.com>
Cc: "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"peterz\@infradead.org" <peterz@infradead.org>,
"gregkh\@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"akpm\@linux-foundation.org" <akpm@linux-foundation.org>,
"mingo\@redhat.com" <mingo@redhat.com>,
"adobriyan\@gmail.com" <adobriyan@gmail.com>,
"serge\@hallyn.com" <serge@hallyn.com>,
"arozansk\@redhat.com" <arozansk@redhat.com>,
"dave\@stgolabs.net" <dave@stgolabs.net>,
"keescook\@chromium.org" <keescook@chromium.org>,
Hans Liljestrand <ishkamiel@gmail.com>,
"David Windsor" <dwindsor@gmail.com>
Subject: Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t
Date: Mon, 10 Jul 2017 03:37:53 -0500 [thread overview]
Message-ID: <87k23gsn4u.fsf@xmission.com> (raw)
In-Reply-To: <2236FBA76BA1254E88B949DDB74E612B6FF2269B@IRSMSX102.ger.corp.intel.com> (Elena Reshetova's message of "Mon, 10 Jul 2017 06:48:22 +0000")
"Reshetova, Elena" <elena.reshetova@intel.com> writes:
2>> Elena Reshetova <elena.reshetova@intel.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.
So there is no benefit to the code, and a non-zero chance that there
will be a typo breaking the code.
All to harden the code for an unlikely future when the code is
updated with a full test cycle and people paying attention.
Introduce a bug now to avoid a bug in the future. That seems like a
very poor engineering trade off.
Eric
next prev parent reply other threads:[~2017-07-10 8:45 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-07 8:59 [PATCH 0/3] v2 ipc subsystem refcount coversions Elena Reshetova
2017-07-07 8:59 ` [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t Elena Reshetova
2017-07-09 21:59 ` Eric W. Biederman
2017-07-10 6:48 ` Reshetova, Elena
2017-07-10 8:37 ` Eric W. Biederman [this message]
2017-07-10 9:34 ` Alexey Dobriyan
2017-07-10 11:19 ` Eric W. Biederman
2017-07-10 9:56 ` Reshetova, Elena
2017-07-10 11:26 ` Eric W. Biederman
2017-07-10 12:11 ` Reshetova, Elena
2017-07-10 20:32 ` Eric W. Biederman
2017-07-12 9:21 ` Reshetova, Elena
2017-07-19 22:35 ` Andrew Morton
2017-07-19 22:54 ` Davidlohr Bueso
2017-07-19 22:58 ` Andrew Morton
2017-07-19 23:11 ` Davidlohr Bueso
2017-07-19 23:20 ` Kees Cook
2017-07-20 0:32 ` Kees Cook
2017-07-20 9:34 ` Ingo Molnar
2017-07-20 12:34 ` Eric W. Biederman
2017-07-20 15:12 ` Kees Cook
2017-07-07 8:59 ` [PATCH 2/3] ipc: convert sem_undo_list.refcnt " Elena Reshetova
2017-07-07 8:59 ` [PATCH 3/3] ipc: convert kern_ipc_perm.refcount " Elena Reshetova
-- strict thread matches above, loose matches on Subject: below --
2017-02-20 11:29 [PATCH 0/3] ipc subsystem refcounter conversions Elena Reshetova
2017-02-20 11:29 ` [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t Elena Reshetova
2017-05-27 19:41 ` Kees Cook
2017-05-28 12:10 ` Manfred Spraul
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