From: Geert Uytterhoeven <geert@linux-m68k.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>,
"David S. Miller" <davem@davemloft.net>,
Greg KH <gregkh@linuxfoundation.org>,
Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
USB list <linux-usb@vger.kernel.org>
Subject: Re: [PATCH] treewide: Replace zero-length arrays with flexible-array member
Date: Thu, 13 Feb 2020 12:09:08 +0100 [thread overview]
Message-ID: <CAMuHMdVZq3Lho0HxEvhv8di=OCBhvNEo=O198b1iayX_Wz_QcA@mail.gmail.com> (raw)
In-Reply-To: <20200211174126.GA29960@embeddedor>
Hi Gustavo,
On Tue, Feb 11, 2020 at 10:49 PM Gustavo A. R. Silva
<gustavo@embeddedor.com> 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
> ];
> };
I've stumbled across one more in include/uapi/linux/usb/ch9.h:
struct usb_key_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 tTKID[3];
__u8 bReserved;
__u8 bKeyData[0];
} __attribute__((packed));
And it seems people are (ab)using one-sized arrays for flexible arrays, too:
struct usb_string_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__le16 wData[1]; /* UTF-16LE encoded */
} __attribute__ ((packed));
As this is UAPI, we have to be careful for regressions, though.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2020-02-13 11:09 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
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 [this message]
2020-02-13 11:11 ` Ard Biesheuvel
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