linux-hardening - Re: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end warning

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Message-ID: <CAOQ4uxg185+i+n_mnXsEaxXYJ1SseDH6RtGreTJDhjkOt6mmSA@mail.gmail.com>
Date: Wed, 6 Mar 2024 09:36:14 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, Jan Kara <jack@...e.cz>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end warning

On Wed, Mar 6, 2024 at 1:52 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Tue, Mar 05, 2024 at 04:18:46PM -0600, Gustavo A. R. Silva wrote:
> > -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> > ready to enable it globally.
> >
> > There is currently a local structure `f` that is using a flexible
> > `struct file_handle` as header for an on-stack place-holder for the
> > flexible-array member `unsigned char f_handle[];`.
> >
> > struct {
> >       struct file_handle handle;
> >       u8 pad[MAX_HANDLE_SZ];
> > } f;
>
> This code pattern is "put a flex array struct on the stack", but we have
> a macro for this now:
>
> DEFINE_FLEX(struct file_handle, handle, f_handle, MAX_HANDLE_SZ);
>
> And you can even include the initializer:
>
> _DEFINE_FLEX(struct file_handle, handle, f_handle, MAX_HANDLE_SZ,
>              = { .handle_bytes = MAX_HANDLE_SZ });
>

Indeed that looks much nicer.

Thanks,
Amir.