From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Kees Cook <keescook@chromium.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>,
linux-crypto@vger.kernel.org, netdev@vger.kernel.org,
linux-usb@vger.kernel.org
Subject: Re: [PATCH] treewide: Replace zero-length arrays with flexible-array member
Date: Tue, 11 Feb 2020 14:30:17 -0600 [thread overview]
Message-ID: <2b73d115-1259-24ae-6f56-e3aa12e5e408@embeddedor.com> (raw)
In-Reply-To: <202002111210.876CEB6@keescook>
On 2/11/20 14:12, Kees Cook wrote:
> On Tue, Feb 11, 2020 at 01:54:22PM -0600, Gustavo A. R. Silva wrote:
>>
>>
>> On 2/11/20 13:38, Greg KH wrote:
>>> On Tue, Feb 11, 2020 at 11:32:04AM -0800, Kees Cook wrote:
>>>> On Tue, Feb 11, 2020 at 01:20:36PM -0600, Gustavo A. R. Silva wrote:
>>>>>
>>>>>
>>>>> On 2/11/20 12:32, Greg KH wrote:
>>>>>> On Tue, Feb 11, 2020 at 11:41:26AM -0600, Gustavo A. R. Silva wrote:
>>>>>>> The current codebase makes use of the zero-length array language
>>>>>>> extension to the C90 standard, but the preferred mechanism to declare
>>>>>>> variable-length types such as these ones is a flexible array member[1][2],
>>>>>>> introduced in C99:
>>>>>>>
>>>>>>> struct foo {
>>>>>>> int stuff;
>>>>>>> struct boo array[];
>>>>>>> };
>>>>>>>
>>>>>>> By making use of the mechanism above, we will get a compiler warning
>>>>>>> in case the flexible array does not occur last in the structure, which
>>>>>>> will help us prevent some kind of undefined behavior bugs from being
>>>>>>> unadvertenly introduced[3] to the codebase from now on.
>>>>>>>
>>>>>>> All these instances of code were found with the help of the following
>>>>>>> Coccinelle script:
>>>>>>>
>>>>>>> @@
>>>>>>> identifier S, member, array;
>>>>>>> type T1, T2;
>>>>>>> @@
>>>>>>>
>>>>>>> struct S {
>>>>>>> ...
>>>>>>> T1 member;
>>>>>>> T2 array[
>>>>>>> - 0
>>>>>>> ];
>>>>>>> };
>>>>>>>
>>>>>>> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
>>>>>>> [2] https://github.com/KSPP/linux/issues/21
>>>>>>> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>>>>>>>
>>>>>>> NOTE: I'll carry this in my -next tree for the v5.6 merge window.
>>>>>>
>>>>>> Why not carve this up into per-subsystem patches so that we can apply
>>>>>> them to our 5.7-rc1 trees and then you submit the "remaining" that don't
>>>>>> somehow get merged at that timeframe for 5.7-rc2?
>>>>>>
>>>>>
>>>>> Yep, sounds good. I'll do that.
>>>>
>>>> FWIW, I'd just like to point out that since this is a mechanical change
>>>> with no code generation differences (unlike the pre-C90 1-byte array
>>>> conversions), it's a way better use of everyone's time to just splat
>>>> this in all at once.
>>>>
>>>> That said, it looks like Gustavo is up for it, but I'd like us to
>>>> generally consider these kinds of mechanical changes as being easier to
>>>> manage in a single patch. (Though getting Acks tends to be a bit
>>>> harder...)
>>>
>>> Hey, if this is such a mechanical patch, let's get it to Linus now,
>>> what's preventing that from being merged now?
>
> Now would be a good time, yes. (Linus has wanted Acks for such things
> sometimes, but those were more "risky" changes...)
>
>> Well, the only thing is that this has never been in linux-next.
>
> Hmm. Was it in one of your 0day-tested trees?
>
It was in my tree for quite a while, but it was never 0day-tested.
Just recently, the 0day guys started testing my _new_ branches,
regularly.
Today, I updated my -next branch to v5.6-rc1 and added the
treewide patch. So, I expect it to be 0day-tested in a couple
of days.
--
Gustavo
next prev parent reply other threads:[~2020-02-11 20:27 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 17:41 [PATCH] treewide: Replace zero-length arrays with flexible-array member Gustavo A. R. Silva
2020-02-11 18:32 ` Greg KH
2020-02-11 19:20 ` Gustavo A. R. Silva
2020-02-11 19:32 ` Kees Cook
2020-02-11 19:38 ` Greg KH
2020-02-11 19:54 ` Gustavo A. R. Silva
2020-02-11 20:12 ` Kees Cook
2020-02-11 20:30 ` Gustavo A. R. Silva [this message]
2020-02-11 19:35 ` Kees Cook
2020-02-11 20:16 ` Gustavo A. R. Silva
2020-02-12 8:00 ` Geert Uytterhoeven
2020-02-12 8:36 ` Kars de Jong
2020-02-13 11:09 ` Geert Uytterhoeven
2020-02-13 11:11 ` Ard Biesheuvel
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